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authorTorvald Riegel <triegel@redhat.com>2014-05-22 16:00:12 +0200
committerTorvald Riegel <triegel@redhat.com>2017-01-10 11:50:17 +0100
commitcc25c8b4c1196a8c29e9a45b1e096b99a87b7f8c (patch)
tree52c5358896bc1ce9ad2081f179e72a1edac5fa6f /nptl/pthread_rwlock_unlock.c
parentfbb31e20bc41957c5f3d6550f0178590cf473043 (diff)
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New pthread rwlock that is more scalable.
This replaces the pthread rwlock with a new implementation that uses a more scalable algorithm (primarily through not using a critical section anymore to make state changes). The fast path for rdlock acquisition and release is now basically a single atomic read-modify write or CAS and a few branches. See nptl/pthread_rwlock_common.c for details. * nptl/DESIGN-rwlock.txt: Remove. * nptl/lowlevelrwlock.sym: Remove. * nptl/Makefile: Add new tests. * nptl/pthread_rwlock_common.c: New file. Contains the new rwlock. * nptl/pthreadP.h (PTHREAD_RWLOCK_PREFER_READER_P): Remove. (PTHREAD_RWLOCK_WRPHASE, PTHREAD_RWLOCK_WRLOCKED, PTHREAD_RWLOCK_RWAITING, PTHREAD_RWLOCK_READER_SHIFT, PTHREAD_RWLOCK_READER_OVERFLOW, PTHREAD_RWLOCK_WRHANDOVER, PTHREAD_RWLOCK_FUTEX_USED): New. * nptl/pthread_rwlock_init.c (__pthread_rwlock_init): Adapt to new implementation. * nptl/pthread_rwlock_rdlock.c (__pthread_rwlock_rdlock_slow): Remove. (__pthread_rwlock_rdlock): Adapt. * nptl/pthread_rwlock_timedrdlock.c (pthread_rwlock_timedrdlock): Adapt. * nptl/pthread_rwlock_timedwrlock.c (pthread_rwlock_timedwrlock): Adapt. * nptl/pthread_rwlock_trywrlock.c (pthread_rwlock_trywrlock): Adapt. * nptl/pthread_rwlock_tryrdlock.c (pthread_rwlock_tryrdlock): Adapt. * nptl/pthread_rwlock_unlock.c (pthread_rwlock_unlock): Adapt. * nptl/pthread_rwlock_wrlock.c (__pthread_rwlock_wrlock_slow): Remove. (__pthread_rwlock_wrlock): Adapt. * nptl/tst-rwlock10.c: Adapt. * nptl/tst-rwlock11.c: Adapt. * nptl/tst-rwlock17.c: New file. * nptl/tst-rwlock18.c: New file. * nptl/tst-rwlock19.c: New file. * nptl/tst-rwlock2b.c: New file. * nptl/tst-rwlock8.c: Adapt. * nptl/tst-rwlock9.c: Adapt. * sysdeps/aarch64/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt. * sysdeps/arm/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt. * sysdeps/hppa/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt. * sysdeps/ia64/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt. * sysdeps/m68k/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt. * sysdeps/microblaze/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt. * sysdeps/mips/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt. * sysdeps/nios2/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt. * sysdeps/s390/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt. * sysdeps/sh/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt. * sysdeps/sparc/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt. * sysdeps/tile/nptl/bits/pthreadtypes.h (pthread_rwlock_t): Adapt. * sysdeps/unix/sysv/linux/alpha/bits/pthreadtypes.h (pthread_rwlock_t): Adapt. * sysdeps/unix/sysv/linux/powerpc/bits/pthreadtypes.h (pthread_rwlock_t): Adapt. * sysdeps/x86/bits/pthreadtypes.h (pthread_rwlock_t): Adapt. * nptl/nptl-printers.py (): Adapt. * nptl/nptl_lock_constants.pysym: Adapt. * nptl/test-rwlock-printers.py: Adapt. * nptl/test-rwlockattr-printers.c: Adapt. * nptl/test-rwlockattr-printers.py: Adapt.
Diffstat (limited to 'nptl/pthread_rwlock_unlock.c')
-rw-r--r--nptl/pthread_rwlock_unlock.c53
1 files changed, 11 insertions, 42 deletions
diff --git a/nptl/pthread_rwlock_unlock.c b/nptl/pthread_rwlock_unlock.c
index 320837d5af..ef46e88263 100644
--- a/nptl/pthread_rwlock_unlock.c
+++ b/nptl/pthread_rwlock_unlock.c
@@ -18,60 +18,29 @@
#include <errno.h>
#include <sysdep.h>
-#include <lowlevellock.h>
#include <futex-internal.h>
#include <pthread.h>
#include <pthreadP.h>
#include <stap-probe.h>
-#include <elide.h>
+#include "pthread_rwlock_common.c"
-/* Unlock RWLOCK. */
+/* See pthread_rwlock_common.c for an overview. */
int
__pthread_rwlock_unlock (pthread_rwlock_t *rwlock)
{
- int futex_shared =
- rwlock->__data.__shared == LLL_PRIVATE ? FUTEX_PRIVATE : FUTEX_SHARED;
-
LIBC_PROBE (rwlock_unlock, 1, rwlock);
- /* Trying to elide an unlocked lock may crash the process. This
- is expected and is compatible with POSIX.1-2008: "results are
- undefined if the read-write lock rwlock is not held by the
- calling thread". */
- if (ELIDE_UNLOCK (rwlock->__data.__writer == 0
- && rwlock->__data.__nr_readers == 0))
- return 0;
-
- lll_lock (rwlock->__data.__lock, rwlock->__data.__shared);
- if (rwlock->__data.__writer)
- rwlock->__data.__writer = 0;
+ /* We distinguish between having acquired a read vs. a write lock by looking
+ at the writer TID. If it's equal to our TID, we must be the writer
+ because nobody else can have stored this value. Also, if we are a
+ reader, we will read from the wrunlock store with value 0 by the most
+ recent writer because that writer happens-before us. */
+ if (atomic_load_relaxed (&rwlock->__data.__cur_writer)
+ == THREAD_GETMEM (THREAD_SELF, tid))
+ __pthread_rwlock_wrunlock (rwlock);
else
- --rwlock->__data.__nr_readers;
- /* If there are still readers present, we do not yet need to wake writers
- nor are responsible to wake any readers. */
- if (rwlock->__data.__nr_readers == 0)
- {
- /* Note that if there is a blocked writer, we effectively make it
- responsible for waking any readers because we don't wake readers in
- this case. */
- if (rwlock->__data.__nr_writers_queued)
- {
- ++rwlock->__data.__writer_wakeup;
- lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
- futex_wake (&rwlock->__data.__writer_wakeup, 1, futex_shared);
- return 0;
- }
- else if (rwlock->__data.__nr_readers_queued)
- {
- ++rwlock->__data.__readers_wakeup;
- lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
- futex_wake (&rwlock->__data.__readers_wakeup, INT_MAX,
- futex_shared);
- return 0;
- }
- }
- lll_unlock (rwlock->__data.__lock, rwlock->__data.__shared);
+ __pthread_rwlock_rdunlock (rwlock);
return 0;
}