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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.
32 lines
418 B
Plaintext
32 lines
418 B
Plaintext
Description:
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Locking in multithreaded situations.
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Files:
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lib/glthread/lock.h
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lib/glthread/lock.c
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m4/lock.m4
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m4/pthread_rwlock_rdlock.m4
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Depends-on:
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extensions
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threadlib
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configure.ac:
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gl_LOCK
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gl_MODULE_INDICATOR([lock])
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Makefile.am:
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lib_SOURCES += glthread/lock.h glthread/lock.c
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Include:
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"glthread/lock.h"
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Link:
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$(LTLIBTHREAD) when linking with libtool, $(LIBTHREAD) otherwise
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License:
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LGPLv2+
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Maintainer:
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all
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