README 61.1 KB
Newer Older
1 2 3 4 5 6
NAME
    IO::AIO - Asynchronous Input/Output

SYNOPSIS
     use IO::AIO;

7
     aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
        my $fh = shift
           or die "/etc/passwd: $!";
        ...
     };

     aio_unlink "/tmp/file", sub { };

     aio_read $fh, 30000, 1024, $buffer, 0, sub {
        $_[0] > 0 or die "read error: $!";
     };

     # version 2+ has request and group objects
     use IO::AIO 2;

     aioreq_pri 4; # give next request a very high priority
     my $req = aio_unlink "/tmp/file", sub { };
     $req->cancel; # cancel request if still in queue

     my $grp = aio_group sub { print "all stats done\n" };
     add $grp aio_stat "..." for ...;

DESCRIPTION
    This module implements asynchronous I/O using whatever means your
31 32
    operating system supports. It is implemented as an interface to "libeio"
    (<http://software.schmorp.de/pkg/libeio.html>).
33 34 35 36 37 38 39 40 41 42 43 44 45 46

    Asynchronous means that operations that can normally block your program
    (e.g. reading from disk) will be done asynchronously: the operation will
    still block, but you can do something else in the meantime. This is
    extremely useful for programs that need to stay interactive even when
    doing heavy I/O (GUI programs, high performance network servers etc.),
    but can also be used to easily do operations in parallel that are
    normally done sequentially, e.g. stat'ing many files, which is much
    faster on a RAID volume or over NFS when you do a number of stat
    operations concurrently.

    While most of this works on all types of file descriptors (for example
    sockets), using these functions on file descriptors that support
    nonblocking operation (again, sockets, pipes etc.) is very inefficient.
47
    Use an event loop for that (such as the EV module): IO::AIO will
48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
    naturally fit into such an event loop itself.

    In this version, a number of threads are started that execute your
    requests and signal their completion. You don't need thread support in
    perl, and the threads created by this module will not be visible to
    perl. In the future, this module might make use of the native aio
    functions available on many operating systems. However, they are often
    not well-supported or restricted (GNU/Linux doesn't allow them on normal
    files currently, for example), and they would only support aio_read and
    aio_write, so the remaining functionality would have to be implemented
    using threads anyway.

    Although the module will work in the presence of other (Perl-) threads,
    it is currently not reentrant in any way, so use appropriate locking
    yourself, always call "poll_cb" from within the same thread, or never
    call "poll_cb" (or other "aio_" functions) recursively.

  EXAMPLE
66 67
    This is a simple example that uses the EV module and loads /etc/passwd
    asynchronously:
68 69

       use Fcntl;
70
       use EV;
71 72
       use IO::AIO;

73 74
       # register the IO::AIO callback with EV
       my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;
75 76

       # queue the request to open /etc/passwd
77
       aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95
          my $fh = shift
             or die "error while opening: $!";

          # stat'ing filehandles is generally non-blocking
          my $size = -s $fh;

          # queue a request to read the file
          my $contents;
          aio_read $fh, 0, $size, $contents, 0, sub {
             $_[0] == $size
                or die "short read: $!";

             close $fh;

             # file contents now in $contents
             print $contents;

             # exit event loop and program
96
             EV::unloop;
97 98 99 100 101 102 103
          };
       };

       # possibly queue up other requests, or open GUI windows,
       # check for sockets etc. etc.

       # process events as long as there are some:
104
       EV::loop;
105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149

REQUEST ANATOMY AND LIFETIME
    Every "aio_*" function creates a request. which is a C data structure
    not directly visible to Perl.

    If called in non-void context, every request function returns a Perl
    object representing the request. In void context, nothing is returned,
    which saves a bit of memory.

    The perl object is a fairly standard ref-to-hash object. The hash
    contents are not used by IO::AIO so you are free to store anything you
    like in it.

    During their existance, aio requests travel through the following
    states, in order:

    ready
        Immediately after a request is created it is put into the ready
        state, waiting for a thread to execute it.

    execute
        A thread has accepted the request for processing and is currently
        executing it (e.g. blocking in read).

    pending
        The request has been executed and is waiting for result processing.

        While request submission and execution is fully asynchronous, result
        processing is not and relies on the perl interpreter calling
        "poll_cb" (or another function with the same effect).

    result
        The request results are processed synchronously by "poll_cb".

        The "poll_cb" function will process all outstanding aio requests by
        calling their callbacks, freeing memory associated with them and
        managing any groups they are contained in.

    done
        Request has reached the end of its lifetime and holds no resources
        anymore (except possibly for the Perl object, but its connection to
        the actual aio request is severed and calling its methods will
        either do nothing or result in a runtime error).

FUNCTIONS
150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172
  QUICK OVERVIEW
    This section simply lists the prototypes of the most important functions
    for quick reference. See the following sections for function-by-function
    documentation.

       aio_open $pathname, $flags, $mode, $callback->($fh)
       aio_close $fh, $callback->($status)
       aio_read  $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
       aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
       aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
       aio_readahead $fh,$offset,$length, $callback->($retval)
       aio_stat  $fh_or_path, $callback->($status)
       aio_lstat $fh, $callback->($status)
       aio_statvfs $fh_or_path, $callback->($statvfs)
       aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
       aio_chown $fh_or_path, $uid, $gid, $callback->($status)
       aio_truncate $fh_or_path, $offset, $callback->($status)
       aio_chmod $fh_or_path, $mode, $callback->($status)
       aio_unlink $pathname, $callback->($status)
       aio_mknod $path, $mode, $dev, $callback->($status)
       aio_link $srcpath, $dstpath, $callback->($status)
       aio_symlink $srcpath, $dstpath, $callback->($status)
       aio_readlink $path, $callback->($link)
173
       aio_realpath $path, $callback->($link)
174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209
       aio_rename $srcpath, $dstpath, $callback->($status)
       aio_mkdir $pathname, $mode, $callback->($status)
       aio_rmdir $pathname, $callback->($status)
       aio_readdir $pathname, $callback->($entries)
       aio_readdirx $pathname, $flags, $callback->($entries, $flags)
          IO::AIO::READDIR_DENTS IO::AIO::READDIR_DIRS_FIRST
          IO::AIO::READDIR_STAT_ORDER IO::AIO::READDIR_FOUND_UNKNOWN
       aio_load $path, $data, $callback->($status)
       aio_copy $srcpath, $dstpath, $callback->($status)
       aio_move $srcpath, $dstpath, $callback->($status)
       aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
       aio_rmtree $path, $callback->($status)
       aio_sync $callback->($status)
       aio_fsync $fh, $callback->($status)
       aio_fdatasync $fh, $callback->($status)
       aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
       aio_pathsync $path, $callback->($status)
       aio_msync $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
       aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0, $callback->($status)
       aio_mlock $scalar, $offset = 0, $length = undef, $callback->($status)
       aio_mlockall $flags, $callback->($status)
       aio_group $callback->(...)
       aio_nop $callback->()

       $prev_pri = aioreq_pri [$pri]
       aioreq_nice $pri_adjust

       IO::AIO::poll_wait
       IO::AIO::poll_cb
       IO::AIO::poll
       IO::AIO::flush
       IO::AIO::max_poll_reqs $nreqs
       IO::AIO::max_poll_time $seconds
       IO::AIO::min_parallel $nthreads
       IO::AIO::max_parallel $nthreads
       IO::AIO::max_idle $nthreads
210
       IO::AIO::idle_timeout $seconds
211 212 213 214 215 216 217 218 219 220 221 222
       IO::AIO::max_outstanding $maxreqs
       IO::AIO::nreqs
       IO::AIO::nready
       IO::AIO::npending

       IO::AIO::sendfile $ofh, $ifh, $offset, $count
       IO::AIO::fadvise $fh, $offset, $len, $advice
       IO::AIO::madvise $scalar, $offset, $length, $advice
       IO::AIO::mprotect $scalar, $offset, $length, $protect
       IO::AIO::munlock $scalar, $offset = 0, $length = undef
       IO::AIO::munlockall

223 224 225 226 227 228
  AIO REQUEST FUNCTIONS
    All the "aio_*" calls are more or less thin wrappers around the syscall
    with the same name (sans "aio_"). The arguments are similar or
    identical, and they all accept an additional (and optional) $callback
    argument which must be a code reference. This code reference will get
    called with the syscall return code (e.g. most syscalls return -1 on
229 230
    error, unlike perl, which usually delivers "false") as its sole argument
    after the given syscall has been executed asynchronously.
231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252

    All functions expecting a filehandle keep a copy of the filehandle
    internally until the request has finished.

    All functions return request objects of type IO::AIO::REQ that allow
    further manipulation of those requests while they are in-flight.

    The pathnames you pass to these routines *must* be absolute and encoded
    as octets. The reason for the former is that at the time the request is
    being executed, the current working directory could have changed.
    Alternatively, you can make sure that you never change the current
    working directory anywhere in the program and then use relative paths.

    To encode pathnames as octets, either make sure you either: a) always
    pass in filenames you got from outside (command line, readdir etc.)
    without tinkering, b) are ASCII or ISO 8859-1, c) use the Encode module
    and encode your pathnames to the locale (or other) encoding in effect in
    the user environment, d) use Glib::filename_from_unicode on unicode
    filenames or e) use something else to ensure your scalar has the correct
    contents.

    This works, btw. independent of the internal UTF-8 bit, which IO::AIO
253
    handles correctly whether it is set or not.
254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302

    $prev_pri = aioreq_pri [$pri]
        Returns the priority value that would be used for the next request
        and, if $pri is given, sets the priority for the next aio request.

        The default priority is 0, the minimum and maximum priorities are -4
        and 4, respectively. Requests with higher priority will be serviced
        first.

        The priority will be reset to 0 after each call to one of the
        "aio_*" functions.

        Example: open a file with low priority, then read something from it
        with higher priority so the read request is serviced before other
        low priority open requests (potentially spamming the cache):

           aioreq_pri -3;
           aio_open ..., sub {
              return unless $_[0];

              aioreq_pri -2;
              aio_read $_[0], ..., sub {
                 ...
              };
           };

    aioreq_nice $pri_adjust
        Similar to "aioreq_pri", but subtracts the given value from the
        current priority, so the effect is cumulative.

    aio_open $pathname, $flags, $mode, $callback->($fh)
        Asynchronously open or create a file and call the callback with a
        newly created filehandle for the file.

        The pathname passed to "aio_open" must be absolute. See API NOTES,
        above, for an explanation.

        The $flags argument is a bitmask. See the "Fcntl" module for a list.
        They are the same as used by "sysopen".

        Likewise, $mode specifies the mode of the newly created file, if it
        didn't exist and "O_CREAT" has been given, just like perl's
        "sysopen", except that it is mandatory (i.e. use 0 if you don't
        create new files, and 0666 or 0777 if you do). Note that the $mode
        will be modified by the umask in effect then the request is being
        executed, so better never change the umask.

        Example:

303
           aio_open "/etc/passwd", IO::AIO::O_RDONLY, 0, sub {
304 305 306 307 308 309 310 311
              if ($_[0]) {
                 print "open successful, fh is $_[0]\n";
                 ...
              } else {
                 die "open failed: $!\n";
              }
           };

312 313 314 315 316 317 318 319 320
        In addition to all the common open modes/flags ("O_RDONLY",
        "O_WRONLY", "O_RDWR", "O_CREAT", "O_TRUNC", "O_EXCL" and
        "O_APPEND"), the following POSIX and non-POSIX constants are
        available (missing ones on your system are, as usual, 0):

        "O_ASYNC", "O_DIRECT", "O_NOATIME", "O_CLOEXEC", "O_NOCTTY",
        "O_NOFOLLOW", "O_NONBLOCK", "O_EXEC", "O_SEARCH", "O_DIRECTORY",
        "O_DSYNC", "O_RSYNC", "O_SYNC" and "O_TTY_INIT".

321 322
    aio_close $fh, $callback->($status)
        Asynchronously close a file and call the callback with the result
323 324 325 326 327
        code.

        Unfortunately, you can't do this to perl. Perl *insists* very
        strongly on closing the file descriptor associated with the
        filehandle itself.
328

329 330 331 332 333 334
        Therefore, "aio_close" will not close the filehandle - instead it
        will use dup2 to overwrite the file descriptor with the write-end of
        a pipe (the pipe fd will be created on demand and will be cached).

        Or in other words: the file descriptor will be closed, but it will
        not be free for reuse until the perl filehandle is closed.
335 336 337

    aio_read $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
    aio_write $fh,$offset,$length, $data,$dataoffset, $callback->($retval)
338 339 340 341 342 343 344
        Reads or writes $length bytes from or to the specified $fh and
        $offset into the scalar given by $data and offset $dataoffset and
        calls the callback without the actual number of bytes read (or -1 on
        error, just like the syscall).

        "aio_read" will, like "sysread", shrink or grow the $data scalar to
        offset plus the actual number of bytes read.
345

346 347 348
        If $offset is undefined, then the current file descriptor offset
        will be used (and updated), otherwise the file descriptor offset
        will not be changed by these calls.
349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372

        If $length is undefined in "aio_write", use the remaining length of
        $data.

        If $dataoffset is less than zero, it will be counted from the end of
        $data.

        The $data scalar *MUST NOT* be modified in any way while the request
        is outstanding. Modifying it can result in segfaults or World War
        III (if the necessary/optional hardware is installed).

        Example: Read 15 bytes at offset 7 into scalar $buffer, starting at
        offset 0 within the scalar:

           aio_read $fh, 7, 15, $buffer, 0, sub {
              $_[0] > 0 or die "read error: $!";
              print "read $_[0] bytes: <$buffer>\n";
           };

    aio_sendfile $out_fh, $in_fh, $in_offset, $length, $callback->($retval)
        Tries to copy $length bytes from $in_fh to $out_fh. It starts
        reading at byte offset $in_offset, and starts writing at the current
        file offset of $out_fh. Because of that, it is not safe to issue
        more than one "aio_sendfile" per $out_fh, as they will interfere
373 374
        with each other. The same $in_fh works fine though, as this function
        does not move or use the file offset of $in_fh.
375

376
        Please note that "aio_sendfile" can read more bytes from $in_fh than
377 378 379 380 381
        are written, and there is no way to find out how many more bytes
        have been read from "aio_sendfile" alone, as "aio_sendfile" only
        provides the number of bytes written to $out_fh. Only if the result
        value equals $length one can assume that $length bytes have been
        read.
382 383 384 385 386 387 388 389 390

        Unlike with other "aio_" functions, it makes a lot of sense to use
        "aio_sendfile" on non-blocking sockets, as long as one end
        (typically the $in_fh) is a file - the file I/O will then be
        asynchronous, while the socket I/O will be non-blocking. Note,
        however, that you can run into a trap where "aio_sendfile" reads
        some data with readahead, then fails to write all data, and when the
        socket is ready the next time, the data in the cache is already
        lost, forcing "aio_sendfile" to again hit the disk. Explicit
391
        "aio_read" + "aio_write" let's you better control resource usage.
392

393
        This call tries to make use of a native "sendfile"-like syscall to
394
        provide zero-copy operation. For this to work, $out_fh should refer
395
        to a socket, and $in_fh should refer to an mmap'able file.
396

397
        If a native sendfile cannot be found or it fails with "ENOSYS",
398 399 400 401 402 403 404 405 406 407 408 409
        "EINVAL", "ENOTSUP", "EOPNOTSUPP", "EAFNOSUPPORT", "EPROTOTYPE" or
        "ENOTSOCK", it will be emulated, so you can call "aio_sendfile" on
        any type of filehandle regardless of the limitations of the
        operating system.

        As native sendfile syscalls (as practically any non-POSIX interface
        hacked together in a hurry to improve benchmark numbers) tend to be
        rather buggy on many systems, this implementation tries to work
        around some known bugs in Linux and FreeBSD kernels (probably
        others, too), but that might fail, so you really really should check
        the return value of "aio_sendfile" - fewre bytes than expected might
        have been transferred.
410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439

    aio_readahead $fh,$offset,$length, $callback->($retval)
        "aio_readahead" populates the page cache with data from a file so
        that subsequent reads from that file will not block on disk I/O. The
        $offset argument specifies the starting point from which data is to
        be read and $length specifies the number of bytes to be read. I/O is
        performed in whole pages, so that offset is effectively rounded down
        to a page boundary and bytes are read up to the next page boundary
        greater than or equal to (off-set+length). "aio_readahead" does not
        read beyond the end of the file. The current file offset of the file
        is left unchanged.

        If that syscall doesn't exist (likely if your OS isn't Linux) it
        will be emulated by simply reading the data, which would have a
        similar effect.

    aio_stat $fh_or_path, $callback->($status)
    aio_lstat $fh, $callback->($status)
        Works like perl's "stat" or "lstat" in void context. The callback
        will be called after the stat and the results will be available
        using "stat _" or "-s _" etc...

        The pathname passed to "aio_stat" must be absolute. See API NOTES,
        above, for an explanation.

        Currently, the stats are always 64-bit-stats, i.e. instead of
        returning an error when stat'ing a large file, the results will be
        silently truncated unless perl itself is compiled with large file
        support.

440 441 442 443 444 445 446 447 448
        To help interpret the mode and dev/rdev stat values, IO::AIO offers
        the following constants and functions (if not implemented, the
        constants will be 0 and the functions will either "croak" or fall
        back on traditional behaviour).

        "S_IFMT", "S_IFIFO", "S_IFCHR", "S_IFBLK", "S_IFLNK", "S_IFREG",
        "S_IFDIR", "S_IFWHT", "S_IFSOCK", "IO::AIO::major $dev_t",
        "IO::AIO::minor $dev_t", "IO::AIO::makedev $major, $minor".

449 450 451 452 453 454 455
        Example: Print the length of /etc/passwd:

           aio_stat "/etc/passwd", sub {
              $_[0] and die "stat failed: $!";
              print "size is ", -s _, "\n";
           };

456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498
    aio_statvfs $fh_or_path, $callback->($statvfs)
        Works like the POSIX "statvfs" or "fstatvfs" syscalls, depending on
        whether a file handle or path was passed.

        On success, the callback is passed a hash reference with the
        following members: "bsize", "frsize", "blocks", "bfree", "bavail",
        "files", "ffree", "favail", "fsid", "flag" and "namemax". On
        failure, "undef" is passed.

        The following POSIX IO::AIO::ST_* constants are defined: "ST_RDONLY"
        and "ST_NOSUID".

        The following non-POSIX IO::AIO::ST_* flag masks are defined to
        their correct value when available, or to 0 on systems that do not
        support them: "ST_NODEV", "ST_NOEXEC", "ST_SYNCHRONOUS",
        "ST_MANDLOCK", "ST_WRITE", "ST_APPEND", "ST_IMMUTABLE",
        "ST_NOATIME", "ST_NODIRATIME" and "ST_RELATIME".

        Example: stat "/wd" and dump out the data if successful.

           aio_statvfs "/wd", sub {
              my $f = $_[0]
                 or die "statvfs: $!";

              use Data::Dumper;
              say Dumper $f;
           };

           # result:
           {
              bsize   => 1024,
              bfree   => 4333064312,
              blocks  => 10253828096,
              files   => 2050765568,
              flag    => 4096,
              favail  => 2042092649,
              bavail  => 4333064312,
              ffree   => 2042092649,
              namemax => 255,
              frsize  => 1024,
              fsid    => 1810
           }

499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545
    aio_utime $fh_or_path, $atime, $mtime, $callback->($status)
        Works like perl's "utime" function (including the special case of
        $atime and $mtime being undef). Fractional times are supported if
        the underlying syscalls support them.

        When called with a pathname, uses utimes(2) if available, otherwise
        utime(2). If called on a file descriptor, uses futimes(2) if
        available, otherwise returns ENOSYS, so this is not portable.

        Examples:

           # set atime and mtime to current time (basically touch(1)):
           aio_utime "path", undef, undef;
           # set atime to current time and mtime to beginning of the epoch:
           aio_utime "path", time, undef; # undef==0

    aio_chown $fh_or_path, $uid, $gid, $callback->($status)
        Works like perl's "chown" function, except that "undef" for either
        $uid or $gid is being interpreted as "do not change" (but -1 can
        also be used).

        Examples:

           # same as "chown root path" in the shell:
           aio_chown "path", 0, -1;
           # same as above:
           aio_chown "path", 0, undef;

    aio_truncate $fh_or_path, $offset, $callback->($status)
        Works like truncate(2) or ftruncate(2).

    aio_chmod $fh_or_path, $mode, $callback->($status)
        Works like perl's "chmod" function.

    aio_unlink $pathname, $callback->($status)
        Asynchronously unlink (delete) a file and call the callback with the
        result code.

    aio_mknod $path, $mode, $dev, $callback->($status)
        [EXPERIMENTAL]

        Asynchronously create a device node (or fifo). See mknod(2).

        The only (POSIX-) portable way of calling this function is:

           aio_mknod $path, IO::AIO::S_IFIFO | $mode, 0, sub { ...

546 547 548
        See "aio_stat" for info about some potentially helpful extra
        constants and functions.

549 550 551 552 553 554 555 556 557 558 559 560 561 562
    aio_link $srcpath, $dstpath, $callback->($status)
        Asynchronously create a new link to the existing object at $srcpath
        at the path $dstpath and call the callback with the result code.

    aio_symlink $srcpath, $dstpath, $callback->($status)
        Asynchronously create a new symbolic link to the existing object at
        $srcpath at the path $dstpath and call the callback with the result
        code.

    aio_readlink $path, $callback->($link)
        Asynchronously read the symlink specified by $path and pass it to
        the callback. If an error occurs, nothing or undef gets passed to
        the callback.

563 564 565 566 567 568 569 570
    aio_realpath $path, $callback->($path)
        Asynchronously make the path absolute and resolve any symlinks in
        $path. The resulting path only consists of directories (Same as
        Cwd::realpath).

        This request can be used to get the absolute path of the current
        working directory by passing it a path of . (a single dot).

571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588
    aio_rename $srcpath, $dstpath, $callback->($status)
        Asynchronously rename the object at $srcpath to $dstpath, just as
        rename(2) and call the callback with the result code.

    aio_mkdir $pathname, $mode, $callback->($status)
        Asynchronously mkdir (create) a directory and call the callback with
        the result code. $mode will be modified by the umask at the time the
        request is executed, so do not change your umask.

    aio_rmdir $pathname, $callback->($status)
        Asynchronously rmdir (delete) a directory and call the callback with
        the result code.

    aio_readdir $pathname, $callback->($entries)
        Unlike the POSIX call of the same name, "aio_readdir" reads an
        entire directory (i.e. opendir + readdir + closedir). The entries
        will not be sorted, and will NOT include the "." and ".." entries.

589 590 591 592 593 594 595 596 597 598 599 600 601
        The callback is passed a single argument which is either "undef" or
        an array-ref with the filenames.

    aio_readdirx $pathname, $flags, $callback->($entries, $flags)
        Quite similar to "aio_readdir", but the $flags argument allows to
        tune behaviour and output format. In case of an error, $entries will
        be "undef".

        The flags are a combination of the following constants, ORed
        together (the flags will also be passed to the callback, possibly
        modified):

        IO::AIO::READDIR_DENTS
602 603 604
            When this flag is off, then the callback gets an arrayref
            consisting of names only (as with "aio_readdir"), otherwise it
            gets an arrayref with "[$name, $type, $inode]" arrayrefs, each
605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626
            describing a single directory entry in more detail.

            $name is the name of the entry.

            $type is one of the "IO::AIO::DT_xxx" constants:

            "IO::AIO::DT_UNKNOWN", "IO::AIO::DT_FIFO", "IO::AIO::DT_CHR",
            "IO::AIO::DT_DIR", "IO::AIO::DT_BLK", "IO::AIO::DT_REG",
            "IO::AIO::DT_LNK", "IO::AIO::DT_SOCK", "IO::AIO::DT_WHT".

            "IO::AIO::DT_UNKNOWN" means just that: readdir does not know. If
            you need to know, you have to run stat yourself. Also, for speed
            reasons, the $type scalars are read-only: you can not modify
            them.

            $inode is the inode number (which might not be exact on systems
            with 64 bit inode numbers and 32 bit perls). This field has
            unspecified content on systems that do not deliver the inode
            information.

        IO::AIO::READDIR_DIRS_FIRST
            When this flag is set, then the names will be returned in an
627 628 629 630
            order where likely directories come first, in optimal stat
            order. This is useful when you need to quickly find directories,
            or you want to find all directories while avoiding to stat()
            each entry.
631 632 633

            If the system returns type information in readdir, then this is
            used to find directories directly. Otherwise, likely directories
634 635
            are names beginning with ".", or otherwise names with no dots,
            of which names with short names are tried first.
636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652

        IO::AIO::READDIR_STAT_ORDER
            When this flag is set, then the names will be returned in an
            order suitable for stat()'ing each one. That is, when you plan
            to stat() all files in the given directory, then the returned
            order will likely be fastest.

            If both this flag and "IO::AIO::READDIR_DIRS_FIRST" are
            specified, then the likely dirs come first, resulting in a less
            optimal stat order.

        IO::AIO::READDIR_FOUND_UNKNOWN
            This flag should not be set when calling "aio_readdirx".
            Instead, it is being set by "aio_readdirx", when any of the
            $type's found were "IO::AIO::DT_UNKNOWN". The absense of this
            flag therefore indicates that all $type's are known, which can
            be used to speed up some algorithms.
653 654 655 656 657 658 659 660

    aio_load $path, $data, $callback->($status)
        This is a composite request that tries to fully load the given file
        into memory. Status is the same as with aio_read.

    aio_copy $srcpath, $dstpath, $callback->($status)
        Try to copy the *file* (directories not supported as either source
        or destination) from $srcpath to $dstpath and call the callback with
661
        a status of 0 (ok) or -1 (error, see $!).
662

663 664 665 666
        This is a composite request that creates the destination file with
        mode 0200 and copies the contents of the source file into it using
        "aio_sendfile", followed by restoring atime, mtime, access mode and
        uid/gid, in that order.
667 668 669 670 671 672 673 674

        If an error occurs, the partial destination file will be unlinked,
        if possible, except when setting atime, mtime, access mode and
        uid/gid, where errors are being ignored.

    aio_move $srcpath, $dstpath, $callback->($status)
        Try to move the *file* (directories not supported as either source
        or destination) from $srcpath to $dstpath and call the callback with
675
        a status of 0 (ok) or -1 (error, see $!).
676

677 678 679
        This is a composite request that tries to rename(2) the file first;
        if rename fails with "EXDEV", it copies the file with "aio_copy"
        and, if that is successful, unlinks the $srcpath.
680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708

    aio_scandir $path, $maxreq, $callback->($dirs, $nondirs)
        Scans a directory (similar to "aio_readdir") but additionally tries
        to efficiently separate the entries of directory $path into two sets
        of names, directories you can recurse into (directories), and ones
        you cannot recurse into (everything else, including symlinks to
        directories).

        "aio_scandir" is a composite request that creates of many sub
        requests_ $maxreq specifies the maximum number of outstanding aio
        requests that this function generates. If it is "<= 0", then a
        suitable default will be chosen (currently 4).

        On error, the callback is called without arguments, otherwise it
        receives two array-refs with path-relative entry names.

        Example:

           aio_scandir $dir, 0, sub {
              my ($dirs, $nondirs) = @_;
              print "real directories: @$dirs\n";
              print "everything else: @$nondirs\n";
           };

        Implementation notes.

        The "aio_readdir" cannot be avoided, but "stat()"'ing every entry
        can.

709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728
        If readdir returns file type information, then this is used directly
        to find directories.

        Otherwise, after reading the directory, the modification time, size
        etc. of the directory before and after the readdir is checked, and
        if they match (and isn't the current time), the link count will be
        used to decide how many entries are directories (if >= 2).
        Otherwise, no knowledge of the number of subdirectories will be
        assumed.

        Then entries will be sorted into likely directories a non-initial
        dot currently) and likely non-directories (see "aio_readdirx"). Then
        every entry plus an appended "/." will be "stat"'ed, likely
        directories first, in order of their inode numbers. If that
        succeeds, it assumes that the entry is a directory or a symlink to
        directory (which will be checked seperately). This is often faster
        than stat'ing the entry itself because filesystems might detect the
        type of the entry without reading the inode data (e.g. ext2fs
        filetype feature), even on systems that cannot return the filetype
        information on readdir.
729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745

        If the known number of directories (link count - 2) has been
        reached, the rest of the entries is assumed to be non-directories.

        This only works with certainty on POSIX (= UNIX) filesystems, which
        fortunately are the vast majority of filesystems around.

        It will also likely work on non-POSIX filesystems with reduced
        efficiency as those tend to return 0 or 1 as link counts, which
        disables the directory counting heuristic.

    aio_rmtree $path, $callback->($status)
        Delete a directory tree starting (and including) $path, return the
        status of the final "rmdir" only. This is a composite request that
        uses "aio_scandir" to recurse into and rmdir directories, and unlink
        everything else.

746 747 748
    aio_sync $callback->($status)
        Asynchronously call sync and call the callback when finished.

749 750 751 752 753 754 755 756 757 758 759
    aio_fsync $fh, $callback->($status)
        Asynchronously call fsync on the given filehandle and call the
        callback with the fsync result code.

    aio_fdatasync $fh, $callback->($status)
        Asynchronously call fdatasync on the given filehandle and call the
        callback with the fdatasync result code.

        If this call isn't available because your OS lacks it or it couldn't
        be detected, it will be emulated by calling "fsync" instead.

760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847 848 849 850 851
    aio_sync_file_range $fh, $offset, $nbytes, $flags, $callback->($status)
        Sync the data portion of the file specified by $offset and $length
        to disk (but NOT the metadata), by calling the Linux-specific
        sync_file_range call. If sync_file_range is not available or it
        returns ENOSYS, then fdatasync or fsync is being substituted.

        $flags can be a combination of
        "IO::AIO::SYNC_FILE_RANGE_WAIT_BEFORE",
        "IO::AIO::SYNC_FILE_RANGE_WRITE" and
        "IO::AIO::SYNC_FILE_RANGE_WAIT_AFTER": refer to the sync_file_range
        manpage for details.

    aio_pathsync $path, $callback->($status)
        This request tries to open, fsync and close the given path. This is
        a composite request intended to sync directories after directory
        operations (E.g. rename). This might not work on all operating
        systems or have any specific effect, but usually it makes sure that
        directory changes get written to disc. It works for anything that
        can be opened for read-only, not just directories.

        Future versions of this function might fall back to other methods
        when "fsync" on the directory fails (such as calling "sync").

        Passes 0 when everything went ok, and -1 on error.

    aio_msync $scalar, $offset = 0, $length = undef, flags = 0,
    $callback->($status)
        This is a rather advanced IO::AIO call, which only works on
        mmap(2)ed scalars (see the "IO::AIO::mmap" function, although it
        also works on data scalars managed by the Sys::Mmap or Mmap modules,
        note that the scalar must only be modified in-place while an aio
        operation is pending on it).

        It calls the "msync" function of your OS, if available, with the
        memory area starting at $offset in the string and ending $length
        bytes later. If $length is negative, counts from the end, and if
        $length is "undef", then it goes till the end of the string. The
        flags can be a combination of "IO::AIO::MS_ASYNC",
        "IO::AIO::MS_INVALIDATE" and "IO::AIO::MS_SYNC".

    aio_mtouch $scalar, $offset = 0, $length = undef, flags = 0,
    $callback->($status)
        This is a rather advanced IO::AIO call, which works best on
        mmap(2)ed scalars.

        It touches (reads or writes) all memory pages in the specified range
        inside the scalar. All caveats and parameters are the same as for
        "aio_msync", above, except for flags, which must be either 0 (which
        reads all pages and ensures they are instantiated) or
        "IO::AIO::MT_MODIFY", which modifies the memory page s(by reading
        and writing an octet from it, which dirties the page).

    aio_mlock $scalar, $offset = 0, $length = undef, $callback->($status)
        This is a rather advanced IO::AIO call, which works best on
        mmap(2)ed scalars.

        It reads in all the pages of the underlying storage into memory (if
        any) and locks them, so they are not getting swapped/paged out or
        removed.

        If $length is undefined, then the scalar will be locked till the
        end.

        On systems that do not implement "mlock", this function returns -1
        and sets errno to "ENOSYS".

        Note that the corresponding "munlock" is synchronous and is
        documented under "MISCELLANEOUS FUNCTIONS".

        Example: open a file, mmap and mlock it - both will be undone when
        $data gets destroyed.

           open my $fh, "<", $path or die "$path: $!";
           my $data;
           IO::AIO::mmap $data, -s $fh, IO::AIO::PROT_READ, IO::AIO::MAP_SHARED, $fh;
           aio_mlock $data; # mlock in background

    aio_mlockall $flags, $callback->($status)
        Calls the "mlockall" function with the given $flags (a combination
        of "IO::AIO::MCL_CURRENT" and "IO::AIO::MCL_FUTURE").

        On systems that do not implement "mlockall", this function returns
        -1 and sets errno to "ENOSYS".

        Note that the corresponding "munlockall" is synchronous and is
        documented under "MISCELLANEOUS FUNCTIONS".

        Example: asynchronously lock all current and future pages into
        memory.

           aio_mlockall IO::AIO::MCL_FUTURE;

852 853 854 855 856 857 858 859 860 861 862 863 864 865 866 867 868 869 870 871 872 873 874 875 876 877 878 879 880 881 882 883 884 885 886 887 888 889 890 891 892 893 894 895 896 897 898 899 900 901 902
    aio_group $callback->(...)
        This is a very special aio request: Instead of doing something, it
        is a container for other aio requests, which is useful if you want
        to bundle many requests into a single, composite, request with a
        definite callback and the ability to cancel the whole request with
        its subrequests.

        Returns an object of class IO::AIO::GRP. See its documentation below
        for more info.

        Example:

           my $grp = aio_group sub {
              print "all stats done\n";
           };

           add $grp
              (aio_stat ...),
              (aio_stat ...),
              ...;

    aio_nop $callback->()
        This is a special request - it does nothing in itself and is only
        used for side effects, such as when you want to add a dummy request
        to a group so that finishing the requests in the group depends on
        executing the given code.

        While this request does nothing, it still goes through the execution
        phase and still requires a worker thread. Thus, the callback will
        not be executed immediately but only after other requests in the
        queue have entered their execution phase. This can be used to
        measure request latency.

    IO::AIO::aio_busy $fractional_seconds, $callback->() *NOT EXPORTED*
        Mainly used for debugging and benchmarking, this aio request puts
        one of the request workers to sleep for the given time.

        While it is theoretically handy to have simple I/O scheduling
        requests like sleep and file handle readable/writable, the overhead
        this creates is immense (it blocks a thread for a long time) so do
        not use this function except to put your application under
        artificial I/O pressure.

  IO::AIO::REQ CLASS
    All non-aggregate "aio_*" functions return an object of this class when
    called in non-void context.

    cancel $req
        Cancels the request, if possible. Has the effect of skipping
        execution when entering the execute state and skipping calling the
        callback when entering the the result state, but will leave the
903 904 905
        request otherwise untouched (with the exception of readdir). That
        means that requests that currently execute will not be stopped and
        resources held by the request will not be freed prematurely.
906 907 908 909 910 911 912 913 914 915 916 917 918 919 920 921 922 923 924 925 926 927 928 929 930 931 932 933 934 935 936 937 938 939 940 941

    cb $req $callback->(...)
        Replace (or simply set) the callback registered to the request.

  IO::AIO::GRP CLASS
    This class is a subclass of IO::AIO::REQ, so all its methods apply to
    objects of this class, too.

    A IO::AIO::GRP object is a special request that can contain multiple
    other aio requests.

    You create one by calling the "aio_group" constructing function with a
    callback that will be called when all contained requests have entered
    the "done" state:

       my $grp = aio_group sub {
          print "all requests are done\n";
       };

    You add requests by calling the "add" method with one or more
    "IO::AIO::REQ" objects:

       $grp->add (aio_unlink "...");

       add $grp aio_stat "...", sub {
          $_[0] or return $grp->result ("error");

          # add another request dynamically, if first succeeded
          add $grp aio_open "...", sub {
             $grp->result ("ok");
          };
       };

    This makes it very easy to create composite requests (see the source of
    "aio_move" for an application) that work and feel like simple requests.

942 943 944 945 946 947 948 949 950 951
    *   The IO::AIO::GRP objects will be cleaned up during calls to
        "IO::AIO::poll_cb", just like any other request.

    *   They can be canceled like any other request. Canceling will cancel
        not only the request itself, but also all requests it contains.

    *   They can also can also be added to other IO::AIO::GRP objects.

    *   You must not add requests to a group from within the group callback
        (or any later time).
952 953 954 955 956 957

    Their lifetime, simplified, looks like this: when they are empty, they
    will finish very quickly. If they contain only requests that are in the
    "done" state, they will also finish. Otherwise they will continue to
    exist.

958 959 960 961 962
    That means after creating a group you have some time to add requests
    (precisely before the callback has been invoked, which is only done
    within the "poll_cb"). And in the callbacks of those requests, you can
    add further requests to the group. And only when all those requests have
    finished will the the group itself finish.
963 964 965 966 967 968 969 970 971 972 973 974 975 976

    add $grp ...
    $grp->add (...)
        Add one or more requests to the group. Any type of IO::AIO::REQ can
        be added, including other groups, as long as you do not create
        circular dependencies.

        Returns all its arguments.

    $grp->cancel_subs
        Cancel all subrequests and clears any feeder, but not the group
        request itself. Useful when you queued a lot of events but got a
        result early.

977 978 979
        The group request will finish normally (you cannot add requests to
        the group).

980 981
    $grp->result (...)
        Set the result value(s) that will be passed to the group callback
982
        when all subrequests have finished and set the groups errno to the
983 984 985 986 987 988 989 990 991 992 993 994 995 996 997 998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013 1014 1015 1016 1017
        current value of errno (just like calling "errno" without an error
        number). By default, no argument will be passed and errno is zero.

    $grp->errno ([$errno])
        Sets the group errno value to $errno, or the current value of errno
        when the argument is missing.

        Every aio request has an associated errno value that is restored
        when the callback is invoked. This method lets you change this value
        from its default (0).

        Calling "result" will also set errno, so make sure you either set $!
        before the call to "result", or call c<errno> after it.

    feed $grp $callback->($grp)
        Sets a feeder/generator on this group: every group can have an
        attached generator that generates requests if idle. The idea behind
        this is that, although you could just queue as many requests as you
        want in a group, this might starve other requests for a potentially
        long time. For example, "aio_scandir" might generate hundreds of
        thousands "aio_stat" requests, delaying any later requests for a
        long time.

        To avoid this, and allow incremental generation of requests, you can
        instead a group and set a feeder on it that generates those
        requests. The feed callback will be called whenever there are few
        enough (see "limit", below) requests active in the group itself and
        is expected to queue more requests.

        The feed callback can queue as many requests as it likes (i.e. "add"
        does not impose any limits).

        If the feed does not queue more requests when called, it will be
        automatically removed from the group.

1018 1019
        If the feed limit is 0 when this method is called, it will be set to
        2 automatically.
1020 1021 1022 1023 1024 1025 1026 1027 1028 1029 1030 1031 1032 1033 1034 1035 1036 1037 1038 1039

        Example:

           # stat all files in @files, but only ever use four aio requests concurrently:

           my $grp = aio_group sub { print "finished\n" };
           limit $grp 4;
           feed $grp sub {
              my $file = pop @files
                 or return;

              add $grp aio_stat $file, sub { ... };
           };

    limit $grp $num
        Sets the feeder limit for the group: The feeder will be called
        whenever the group contains less than this many requests.

        Setting the limit to 0 will pause the feeding process.

1040 1041 1042
        The default value for the limit is 0, but note that setting a feeder
        automatically bumps it up to 2.

1043 1044 1045 1046 1047
  SUPPORT FUNCTIONS
   EVENT PROCESSING AND EVENT LOOP INTEGRATION
    $fileno = IO::AIO::poll_fileno
        Return the *request result pipe file descriptor*. This filehandle
        must be polled for reading by some mechanism outside this module
1048 1049 1050
        (e.g. EV, Glib, select and so on, see below or the SYNOPSIS). If the
        pipe becomes readable you have to call "poll_cb" to check the
        results.
1051 1052 1053 1054 1055

        See "poll_cb" for an example.

    IO::AIO::poll_cb
        Process some outstanding events on the result pipe. You have to call
1056 1057 1058 1059 1060
        this regularly. Returns 0 if all events could be processed (or there
        were no events to process), or -1 if it returned earlier for
        whatever reason. Returns immediately when no events are outstanding.
        The amount of events processed depends on the settings of
        "IO::AIO::max_poll_req" and "IO::AIO::max_poll_time".
1061 1062

        If not all requests were processed for whatever reason, the
1063 1064
        filehandle will still be ready when "poll_cb" returns, so normally
        you don't have to do anything special to have it called later.
1065

1066 1067 1068 1069 1070 1071 1072
        Apart from calling "IO::AIO::poll_cb" when the event filehandle
        becomes ready, it can be beneficial to call this function from loops
        which submit a lot of requests, to make sure the results get
        processed when they become available and not just when the loop is
        finished and the event loop takes over again. This function returns
        very fast when there are no outstanding requests.

1073
        Example: Install an Event watcher that automatically calls
1074 1075
        IO::AIO::poll_cb with high priority (more examples can be found in
        the SYNOPSIS section, at the top of this document):
1076 1077 1078 1079 1080

           Event->io (fd => IO::AIO::poll_fileno,
                      poll => 'r', async => 1,
                      cb => \&IO::AIO::poll_cb);

1081 1082 1083 1084 1085 1086 1087 1088 1089 1090 1091 1092 1093 1094 1095 1096 1097 1098 1099 1100 1101 1102 1103 1104
    IO::AIO::poll_wait
        If there are any outstanding requests and none of them in the result
        phase, wait till the result filehandle becomes ready for reading
        (simply does a "select" on the filehandle. This is useful if you
        want to synchronously wait for some requests to finish).

        See "nreqs" for an example.

    IO::AIO::poll
        Waits until some requests have been handled.

        Returns the number of requests processed, but is otherwise strictly
        equivalent to:

           IO::AIO::poll_wait, IO::AIO::poll_cb

    IO::AIO::flush
        Wait till all outstanding AIO requests have been handled.

        Strictly equivalent to:

           IO::AIO::poll_wait, IO::AIO::poll_cb
              while IO::AIO::nreqs;

1105 1106 1107 1108 1109 1110 1111 1112 1113 1114 1115 1116 1117 1118 1119 1120 1121 1122 1123 1124 1125 1126 1127 1128 1129 1130 1131 1132 1133 1134 1135 1136 1137 1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162 1163 1164 1165 1166 1167 1168 1169 1170 1171 1172 1173 1174
    IO::AIO::max_poll_reqs $nreqs
    IO::AIO::max_poll_time $seconds
        These set the maximum number of requests (default 0, meaning
        infinity) that are being processed by "IO::AIO::poll_cb" in one
        call, respectively the maximum amount of time (default 0, meaning
        infinity) spent in "IO::AIO::poll_cb" to process requests (more
        correctly the mininum amount of time "poll_cb" is allowed to use).

        Setting "max_poll_time" to a non-zero value creates an overhead of
        one syscall per request processed, which is not normally a problem
        unless your callbacks are really really fast or your OS is really
        really slow (I am not mentioning Solaris here). Using
        "max_poll_reqs" incurs no overhead.

        Setting these is useful if you want to ensure some level of
        interactiveness when perl is not fast enough to process all requests
        in time.

        For interactive programs, values such as 0.01 to 0.1 should be fine.

        Example: Install an Event watcher that automatically calls
        IO::AIO::poll_cb with low priority, to ensure that other parts of
        the program get the CPU sometimes even under high AIO load.

           # try not to spend much more than 0.1s in poll_cb
           IO::AIO::max_poll_time 0.1;

           # use a low priority so other tasks have priority
           Event->io (fd => IO::AIO::poll_fileno,
                      poll => 'r', nice => 1,
                      cb => &IO::AIO::poll_cb);

   CONTROLLING THE NUMBER OF THREADS
    IO::AIO::min_parallel $nthreads
        Set the minimum number of AIO threads to $nthreads. The current
        default is 8, which means eight asynchronous operations can execute
        concurrently at any one time (the number of outstanding requests,
        however, is unlimited).

        IO::AIO starts threads only on demand, when an AIO request is queued
        and no free thread exists. Please note that queueing up a hundred
        requests can create demand for a hundred threads, even if it turns
        out that everything is in the cache and could have been processed
        faster by a single thread.

        It is recommended to keep the number of threads relatively low, as
        some Linux kernel versions will scale negatively with the number of
        threads (higher parallelity => MUCH higher latency). With current
        Linux 2.6 versions, 4-32 threads should be fine.

        Under most circumstances you don't need to call this function, as
        the module selects a default that is suitable for low to moderate
        load.

    IO::AIO::max_parallel $nthreads
        Sets the maximum number of AIO threads to $nthreads. If more than
        the specified number of threads are currently running, this function
        kills them. This function blocks until the limit is reached.

        While $nthreads are zero, aio requests get queued but not executed
        until the number of threads has been increased again.

        This module automatically runs "max_parallel 0" at program end, to
        ensure that all threads are killed and that there are no outstanding
        requests.

        Under normal circumstances you don't need to call this function.

    IO::AIO::max_idle $nthreads
        Limit the number of threads (default: 4) that are allowed to idle
1175 1176 1177 1178
        (i.e., threads that did not get a request to process within the idle
        timeout (default: 10 seconds). That means if a thread becomes idle
        while $nthreads other threads are also idle, it will free its
        resources and exit.
1179 1180 1181 1182 1183 1184 1185 1186 1187 1188

        This is useful when you allow a large number of threads (e.g. 100 or
        1000) to allow for extremely high load situations, but want to free
        resources under normal circumstances (1000 threads can easily
        consume 30MB of RAM).

        The default is probably ok in most situations, especially if thread
        creation is fast. If thread creation is very slow on your system you
        might want to use larger values.

1189 1190 1191 1192
    IO::AIO::idle_timeout $seconds
        Sets the minimum idle timeout (default 10) after which worker
        threads are allowed to exit. SEe "IO::AIO::max_idle".

1193
    IO::AIO::max_outstanding $maxreqs
1194 1195 1196 1197 1198 1199 1200 1201 1202
        Sets the maximum number of outstanding requests to $nreqs. If you do
        queue up more than this number of requests, the next call to
        "IO::AIO::poll_cb" (and other functions calling "poll_cb", such as
        "IO::AIO::flush" or "IO::AIO::poll") will block until the limit is
        no longer exceeded.

        In other words, this setting does not enforce a queue limit, but can
        be used to make poll functions block if the limit is exceeded.

1203 1204 1205 1206
        This is a very bad function to use in interactive programs because
        it blocks, and a bad way to reduce concurrency because it is
        inexact: Better use an "aio_group" together with a feed callback.

1207 1208 1209 1210 1211 1212 1213 1214 1215 1216 1217
        It's main use is in scripts without an event loop - when you want to
        stat a lot of files, you can write somehting like this:

           IO::AIO::max_outstanding 32;

           for my $path (...) {
              aio_stat $path , ...;
              IO::AIO::poll_cb;
           }

           IO::AIO::flush;
1218

1219 1220 1221 1222 1223
        The call to "poll_cb" inside the loop will normally return
        instantly, but as soon as more thna 32 reqeusts are in-flight, it
        will block until some requests have been handled. This keeps the
        loop from pushing a large number of "aio_stat" requests onto the
        queue.
1224

1225 1226
        The default value for "max_outstanding" is very large, so there is
        no practical limit on the number of outstanding requests.
1227 1228 1229 1230 1231 1232 1233 1234 1235 1236 1237 1238 1239 1240 1241 1242 1243 1244 1245 1246

   STATISTICAL INFORMATION
    IO::AIO::nreqs
        Returns the number of requests currently in the ready, execute or
        pending states (i.e. for which their callback has not been invoked
        yet).

        Example: wait till there are no outstanding requests anymore:

           IO::AIO::poll_wait, IO::AIO::poll_cb
              while IO::AIO::nreqs;

    IO::AIO::nready
        Returns the number of requests currently in the ready state (not yet
        executed).

    IO::AIO::npending
        Returns the number of requests currently in the pending state
        (executed, but not yet processed by poll_cb).

1247 1248 1249 1250 1251 1252 1253 1254 1255 1256 1257 1258 1259 1260 1261 1262 1263 1264 1265 1266 1267 1268 1269 1270 1271 1272 1273 1274 1275 1276 1277 1278 1279 1280 1281 1282 1283 1284 1285 1286 1287 1288 1289 1290 1291 1292 1293 1294 1295 1296 1297 1298 1299 1300 1301 1302 1303 1304 1305 1306 1307 1308 1309 1310 1311 1312 1313 1314 1315 1316 1317 1318 1319 1320 1321 1322 1323 1324 1325 1326 1327 1328 1329 1330 1331 1332 1333 1334 1335 1336 1337 1338 1339 1340 1341 1342 1343 1344 1345 1346 1347 1348 1349 1350 1351 1352 1353 1354 1355 1356 1357 1358 1359 1360 1361 1362 1363 1364 1365 1366 1367 1368 1369 1370 1371 1372 1373 1374 1375 1376 1377 1378 1379 1380
   MISCELLANEOUS FUNCTIONS
    IO::AIO implements some functions that might be useful, but are not
    asynchronous.

    IO::AIO::sendfile $ofh, $ifh, $offset, $count
        Calls the "eio_sendfile_sync" function, which is like
        "aio_sendfile", but is blocking (this makes most sense if you know
        the input data is likely cached already and the output filehandle is
        set to non-blocking operations).

        Returns the number of bytes copied, or -1 on error.

    IO::AIO::fadvise $fh, $offset, $len, $advice
        Simply calls the "posix_fadvise" function (see its manpage for
        details). The following advice constants are avaiable:
        "IO::AIO::FADV_NORMAL", "IO::AIO::FADV_SEQUENTIAL",
        "IO::AIO::FADV_RANDOM", "IO::AIO::FADV_NOREUSE",
        "IO::AIO::FADV_WILLNEED", "IO::AIO::FADV_DONTNEED".

        On systems that do not implement "posix_fadvise", this function
        returns ENOSYS, otherwise the return value of "posix_fadvise".

    IO::AIO::madvise $scalar, $offset, $len, $advice
        Simply calls the "posix_madvise" function (see its manpage for
        details). The following advice constants are avaiable:
        "IO::AIO::MADV_NORMAL", "IO::AIO::MADV_SEQUENTIAL",
        "IO::AIO::MADV_RANDOM", "IO::AIO::MADV_WILLNEED",
        "IO::AIO::MADV_DONTNEED".

        On systems that do not implement "posix_madvise", this function
        returns ENOSYS, otherwise the return value of "posix_madvise".

    IO::AIO::mprotect $scalar, $offset, $len, $protect
        Simply calls the "mprotect" function on the preferably AIO::mmap'ed
        $scalar (see its manpage for details). The following protect
        constants are avaiable: "IO::AIO::PROT_NONE", "IO::AIO::PROT_READ",
        "IO::AIO::PROT_WRITE", "IO::AIO::PROT_EXEC".

        On systems that do not implement "mprotect", this function returns
        ENOSYS, otherwise the return value of "mprotect".

    IO::AIO::mmap $scalar, $length, $prot, $flags, $fh[, $offset]
        Memory-maps a file (or anonymous memory range) and attaches it to
        the given $scalar, which will act like a string scalar.

        The only operations allowed on the scalar are "substr"/"vec" that
        don't change the string length, and most read-only operations such
        as copying it or searching it with regexes and so on.

        Anything else is unsafe and will, at best, result in memory leaks.

        The memory map associated with the $scalar is automatically removed
        when the $scalar is destroyed, or when the "IO::AIO::mmap" or
        "IO::AIO::munmap" functions are called.

        This calls the "mmap"(2) function internally. See your system's
        manual page for details on the $length, $prot and $flags parameters.

        The $length must be larger than zero and smaller than the actual
        filesize.

        $prot is a combination of "IO::AIO::PROT_NONE",
        "IO::AIO::PROT_EXEC", "IO::AIO::PROT_READ" and/or
        "IO::AIO::PROT_WRITE",

        $flags can be a combination of "IO::AIO::MAP_SHARED" or
        "IO::AIO::MAP_PRIVATE", or a number of system-specific flags (when
        not available, the are defined as 0): "IO::AIO::MAP_ANONYMOUS"
        (which is set to "MAP_ANON" if your system only provides this
        constant), "IO::AIO::MAP_HUGETLB", "IO::AIO::MAP_LOCKED",
        "IO::AIO::MAP_NORESERVE", "IO::AIO::MAP_POPULATE" or
        "IO::AIO::MAP_NONBLOCK"

        If $fh is "undef", then a file descriptor of -1 is passed.

        $offset is the offset from the start of the file - it generally must
        be a multiple of "IO::AIO::PAGESIZE" and defaults to 0.

        Example:

           use Digest::MD5;
           use IO::AIO;

           open my $fh, "<verybigfile"
              or die "$!";

           IO::AIO::mmap my $data, -s $fh, IO::AIO::PROT_READ, IO::AIO::MAP_SHARED, $fh
              or die "verybigfile: $!";

           my $fast_md5 = md5 $data;

    IO::AIO::munmap $scalar
        Removes a previous mmap and undefines the $scalar.

    IO::AIO::munlock $scalar, $offset = 0, $length = undef
        Calls the "munlock" function, undoing the effects of a previous
        "aio_mlock" call (see its description for details).

    IO::AIO::munlockall
        Calls the "munlockall" function.

        On systems that do not implement "munlockall", this function returns
        ENOSYS, otherwise the return value of "munlockall".

EVENT LOOP INTEGRATION
    It is recommended to use AnyEvent::AIO to integrate IO::AIO
    automatically into many event loops:

     # AnyEvent integration (EV, Event, Glib, Tk, POE, urxvt, pureperl...)
     use AnyEvent::AIO;

    You can also integrate IO::AIO manually into many event loops, here are
    some examples of how to do this:

     # EV integration
     my $aio_w = EV::io IO::AIO::poll_fileno, EV::READ, \&IO::AIO::poll_cb;

     # Event integration
     Event->io (fd => IO::AIO::poll_fileno,
                poll => 'r',
                cb => \&IO::AIO::poll_cb);

     # Glib/Gtk2 integration
     add_watch Glib::IO IO::AIO::poll_fileno,
               in => sub { IO::AIO::poll_cb; 1 };

     # Tk integration
     Tk::Event::IO->fileevent (IO::AIO::poll_fileno, "",
                               readable => \&IO::AIO::poll_cb);

     # Danga::Socket integration
     Danga::Socket->AddOtherFds (IO::AIO::poll_fileno =>
                                 \&IO::AIO::poll_cb);

1381
  FORK BEHAVIOUR
1382 1383 1384
    Usage of pthreads in a program changes the semantics of fork
    considerably. Specifically, only async-safe functions can be called
    after fork. Perl doesn't know about this, so in general, you cannot call
1385 1386 1387 1388 1389 1390 1391 1392 1393 1394 1395 1396 1397 1398 1399 1400 1401 1402 1403 1404 1405 1406 1407
    fork with defined behaviour in perl if pthreads are involved. IO::AIO
    uses pthreads, so this applies, but many other extensions and (for
    inexplicable reasons) perl itself often is linked against pthreads, so
    this limitation applies to quite a lot of perls.

    This module no longer tries to fight your OS, or POSIX. That means
    IO::AIO only works in the process that loaded it. Forking is fully
    supported, but using IO::AIO in the child is not.

    You might get around by not *using* IO::AIO before (or after) forking.
    You could also try to call the IO::AIO::reinit function in the child:

    IO::AIO::reinit
        Abondons all current requests and I/O threads and simply
        reinitialises all data structures. This is not an operation
        suppported by any standards, but happens to work on GNU/Linux and
        some newer BSD systems.

        The only reasonable use for this function is to call it after
        forking, if "IO::AIO" was used in the parent. Calling it while
        IO::AIO is active in the process will result in undefined behaviour.
        Calling it at any time will also result in any undefined (by POSIX)
        behaviour.
1408 1409 1410 1411 1412 1413 1414 1415 1416 1417

  MEMORY USAGE
    Per-request usage:

    Each aio request uses - depending on your architecture - around 100-200
    bytes of memory. In addition, stat requests need a stat buffer (possibly
    a few hundred bytes), readdir requires a result buffer and so on. Perl
    scalars and other data passed into aio requests will also be locked and
    will consume memory till the request has entered the done state.

1418
    This is not awfully much, so queuing lots of requests is not usually a
1419 1420 1421 1422 1423 1424 1425 1426 1427 1428 1429 1430
    problem.

    Per-thread usage:

    In the execution phase, some aio requests require more memory for
    temporary buffers, and each thread requires a stack and other data
    structures (usually around 16k-128k, depending on the OS).

KNOWN BUGS
    Known bugs will be fixed in the next release.

SEE ALSO
1431 1432
    AnyEvent::AIO for easy integration into event loops, Coro::AIO for a
    more natural syntax.
1433 1434 1435 1436 1437

AUTHOR
     Marc Lehmann <schmorp@schmorp.de>
     http://home.schmorp.de/