1. 18 Jun, 2018 1 commit
    • Bruno Haible's avatar
      pthread_rwlock_rdlock: Add comments regarding glibc behaviour. · 8584beae
      Bruno Haible authored
      * m4/pthread_rwlock_rdlock.m4: Add comment.
      * doc/posix-functions/pthread_rwlock_rdlock.texi: Mention that rwlocks
      are reader-preferring in glibc.
      * doc/posix-functions/pthread_rwlock_tryrdlock.texi: Likwise.
      * doc/posix-functions/pthread_rwlock_timedrdlock.texi: Likewise.
      8584beae
  2. 01 Jan, 2018 1 commit
  3. 05 Jan, 2017 1 commit
    • Bruno Haible's avatar
      lock: Provide guarantee to avoid writer starvation for rwlocks. · be95b17a
      Bruno Haible authored
      The rationale is: 1) Read-preferring read-write locks are prone to
      writer starvation if the number of reader threads multiplied by the
      percentage of time they have the lock held is too high. 2) Write-
      preferring read-write locks are the only reliable way to avoid this.
      3) There have been reports of 'test-lock' hanging on glibc systems
      http://lists.gnu.org/archive/html/bug-gnulib/2017-01/msg00009.html,
      and glibc indeed implements read-preferring rwlocks by default, see
      http://man7.org/linux/man-pages/man3/pthread_rwlockattr_setkind_np.3.html
      and https://sourceware.org/bugzilla/show_bug.cgi?id=13701 .
      
      * m4/pthread_rwlock_rdlock.m4: New file.
      * m4/lock.m4 (gl_LOCK): Invoke gl_PTHREAD_RWLOCK_RDLOCK_PREFER_WRITER.
      * lib/glthread/lock.h [USE_POSIX_THREADS]: Test
      HAVE_PTHREAD_RWLOCK_RDLOCK_PREFER_WRITER. Use a different implementation
      of rwlock initialization on glibc systems without
      HAVE_PTHREAD_RWLOCK_RDLOCK_PREFER_WRITER. Use a different implementation
      of rwlocks altogether on non-glibc systems without
      HAVE_PTHREAD_RWLOCK_RDLOCK_PREFER_WRITER.
      [USE_PTH_THREADS]: Use a different implementation of rwlocks altogether.
      * lib/glthread/lock.c [USE_POSIX_THREADS]
      (glthread_rwlock_init_for_glibc): New function.
      [USE_POSIX_THREADS] (glthread_rwlock_rdlock_multithreaded): Update
      comment.
      [USE_PTH_THREADS]: New implementation of rwlocks.
      [USE_WINDOWS_THREADS] (glthread_rwlock_rdlock_func): Prefer writers over
      readers.
      * modules/lock (Files): Add m4/pthread_rwlock_rdlock.m4.
      (Depends-on): Add 'extensions'.
      * tests/test-rwlock1.c: New file.
      * lock-tests (Files): Add it.
      (Depends-on): Add usleep.
      (Makefile.am): Add test-rwlock1 to the tests.
      be95b17a