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e8c659d74e
Add elision paths to the basic mutex locks. The normal path has a check for RTM and upgrades the lock to RTM when available. Trylocks cannot automatically upgrade, so they check for elision every time. We use a 4 byte value in the mutex to store the lock elision adaptation state. This is separate from the adaptive spin state and uses a separate field. Condition variables currently do not support elision. Recursive mutexes and condition variables may be supported at some point, but are not in the current implementation. Also "trylock" will not automatically enable elision unless some other lock call has been already called on the lock. This version does not use IFUNC, so it means every lock has one additional check for elision. Benchmarking showed the overhead to be negligible.
408 lines
11 KiB
C
408 lines
11 KiB
C
/* Copyright (C) 2002-2013 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<http://www.gnu.org/licenses/>. */
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#include <assert.h>
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#include <errno.h>
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#include <stdlib.h>
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#include "pthreadP.h"
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#include <lowlevellock.h>
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#ifndef lll_trylock_elision
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#define lll_trylock_elision(a,t) lll_trylock(a)
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#endif
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#ifndef DO_ELISION
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#define DO_ELISION(m) 0
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#endif
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/* We don't force elision in trylock, because this can lead to inconsistent
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lock state if the lock was actually busy. */
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int
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__pthread_mutex_trylock (mutex)
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pthread_mutex_t *mutex;
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{
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int oldval;
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pid_t id = THREAD_GETMEM (THREAD_SELF, tid);
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switch (__builtin_expect (PTHREAD_MUTEX_TYPE_ELISION (mutex),
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PTHREAD_MUTEX_TIMED_NP))
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{
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/* Recursive mutex. */
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case PTHREAD_MUTEX_RECURSIVE_NP|PTHREAD_MUTEX_ELISION_NP:
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case PTHREAD_MUTEX_RECURSIVE_NP:
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/* Check whether we already hold the mutex. */
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if (mutex->__data.__owner == id)
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{
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/* Just bump the counter. */
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if (__builtin_expect (mutex->__data.__count + 1 == 0, 0))
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/* Overflow of the counter. */
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return EAGAIN;
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++mutex->__data.__count;
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return 0;
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}
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if (lll_trylock (mutex->__data.__lock) == 0)
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{
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/* Record the ownership. */
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mutex->__data.__owner = id;
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mutex->__data.__count = 1;
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++mutex->__data.__nusers;
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return 0;
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}
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break;
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case PTHREAD_MUTEX_TIMED_ELISION_NP:
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elision:
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if (lll_trylock_elision (mutex->__data.__lock,
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mutex->__data.__elision) != 0)
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break;
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/* Don't record the ownership. */
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return 0;
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case PTHREAD_MUTEX_TIMED_NP:
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if (DO_ELISION (mutex))
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goto elision;
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/*FALL THROUGH*/
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case PTHREAD_MUTEX_ADAPTIVE_NP:
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case PTHREAD_MUTEX_ERRORCHECK_NP:
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if (lll_trylock (mutex->__data.__lock) != 0)
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break;
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/* Record the ownership. */
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mutex->__data.__owner = id;
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++mutex->__data.__nusers;
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return 0;
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case PTHREAD_MUTEX_ROBUST_RECURSIVE_NP:
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case PTHREAD_MUTEX_ROBUST_ERRORCHECK_NP:
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case PTHREAD_MUTEX_ROBUST_NORMAL_NP:
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case PTHREAD_MUTEX_ROBUST_ADAPTIVE_NP:
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
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&mutex->__data.__list.__next);
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oldval = mutex->__data.__lock;
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do
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{
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again:
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if ((oldval & FUTEX_OWNER_DIED) != 0)
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{
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/* The previous owner died. Try locking the mutex. */
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int newval = id | (oldval & FUTEX_WAITERS);
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newval
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= atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
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newval, oldval);
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if (newval != oldval)
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{
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oldval = newval;
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goto again;
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}
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/* We got the mutex. */
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mutex->__data.__count = 1;
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/* But it is inconsistent unless marked otherwise. */
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mutex->__data.__owner = PTHREAD_MUTEX_INCONSISTENT;
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ENQUEUE_MUTEX (mutex);
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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/* Note that we deliberately exist here. If we fall
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through to the end of the function __nusers would be
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incremented which is not correct because the old
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owner has to be discounted. */
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return EOWNERDEAD;
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}
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/* Check whether we already hold the mutex. */
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if (__builtin_expect ((oldval & FUTEX_TID_MASK) == id, 0))
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{
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int kind = PTHREAD_MUTEX_TYPE (mutex);
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if (kind == PTHREAD_MUTEX_ROBUST_ERRORCHECK_NP)
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{
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
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NULL);
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return EDEADLK;
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}
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if (kind == PTHREAD_MUTEX_ROBUST_RECURSIVE_NP)
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{
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
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NULL);
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/* Just bump the counter. */
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if (__builtin_expect (mutex->__data.__count + 1 == 0, 0))
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/* Overflow of the counter. */
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return EAGAIN;
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++mutex->__data.__count;
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return 0;
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}
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}
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oldval = lll_robust_trylock (mutex->__data.__lock, id);
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if (oldval != 0 && (oldval & FUTEX_OWNER_DIED) == 0)
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{
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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return EBUSY;
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}
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if (__builtin_expect (mutex->__data.__owner
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== PTHREAD_MUTEX_NOTRECOVERABLE, 0))
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{
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/* This mutex is now not recoverable. */
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mutex->__data.__count = 0;
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if (oldval == id)
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lll_unlock (mutex->__data.__lock,
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PTHREAD_ROBUST_MUTEX_PSHARED (mutex));
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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return ENOTRECOVERABLE;
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}
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}
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while ((oldval & FUTEX_OWNER_DIED) != 0);
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ENQUEUE_MUTEX (mutex);
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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mutex->__data.__owner = id;
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++mutex->__data.__nusers;
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mutex->__data.__count = 1;
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return 0;
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case PTHREAD_MUTEX_PI_RECURSIVE_NP:
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case PTHREAD_MUTEX_PI_ERRORCHECK_NP:
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case PTHREAD_MUTEX_PI_NORMAL_NP:
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case PTHREAD_MUTEX_PI_ADAPTIVE_NP:
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case PTHREAD_MUTEX_PI_ROBUST_RECURSIVE_NP:
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case PTHREAD_MUTEX_PI_ROBUST_ERRORCHECK_NP:
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case PTHREAD_MUTEX_PI_ROBUST_NORMAL_NP:
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case PTHREAD_MUTEX_PI_ROBUST_ADAPTIVE_NP:
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{
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int kind = mutex->__data.__kind & PTHREAD_MUTEX_KIND_MASK_NP;
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int robust = mutex->__data.__kind & PTHREAD_MUTEX_ROBUST_NORMAL_NP;
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if (robust)
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/* Note: robust PI futexes are signaled by setting bit 0. */
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending,
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(void *) (((uintptr_t) &mutex->__data.__list.__next)
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| 1));
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oldval = mutex->__data.__lock;
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/* Check whether we already hold the mutex. */
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if (__builtin_expect ((oldval & FUTEX_TID_MASK) == id, 0))
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{
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if (kind == PTHREAD_MUTEX_ERRORCHECK_NP)
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{
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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return EDEADLK;
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}
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if (kind == PTHREAD_MUTEX_RECURSIVE_NP)
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{
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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/* Just bump the counter. */
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if (__builtin_expect (mutex->__data.__count + 1 == 0, 0))
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/* Overflow of the counter. */
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return EAGAIN;
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++mutex->__data.__count;
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return 0;
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}
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}
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oldval
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= atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
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id, 0);
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if (oldval != 0)
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{
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if ((oldval & FUTEX_OWNER_DIED) == 0)
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{
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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return EBUSY;
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}
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assert (robust);
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/* The mutex owner died. The kernel will now take care of
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everything. */
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int private = (robust
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? PTHREAD_ROBUST_MUTEX_PSHARED (mutex)
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: PTHREAD_MUTEX_PSHARED (mutex));
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INTERNAL_SYSCALL_DECL (__err);
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int e = INTERNAL_SYSCALL (futex, __err, 4, &mutex->__data.__lock,
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__lll_private_flag (FUTEX_TRYLOCK_PI,
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private), 0, 0);
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if (INTERNAL_SYSCALL_ERROR_P (e, __err)
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&& INTERNAL_SYSCALL_ERRNO (e, __err) == EWOULDBLOCK)
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{
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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return EBUSY;
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}
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oldval = mutex->__data.__lock;
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}
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if (__builtin_expect (oldval & FUTEX_OWNER_DIED, 0))
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{
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atomic_and (&mutex->__data.__lock, ~FUTEX_OWNER_DIED);
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/* We got the mutex. */
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mutex->__data.__count = 1;
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/* But it is inconsistent unless marked otherwise. */
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mutex->__data.__owner = PTHREAD_MUTEX_INCONSISTENT;
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ENQUEUE_MUTEX (mutex);
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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/* Note that we deliberately exit here. If we fall
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through to the end of the function __nusers would be
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incremented which is not correct because the old owner
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has to be discounted. */
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return EOWNERDEAD;
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}
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if (robust
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&& __builtin_expect (mutex->__data.__owner
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== PTHREAD_MUTEX_NOTRECOVERABLE, 0))
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{
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/* This mutex is now not recoverable. */
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mutex->__data.__count = 0;
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INTERNAL_SYSCALL_DECL (__err);
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INTERNAL_SYSCALL (futex, __err, 4, &mutex->__data.__lock,
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__lll_private_flag (FUTEX_UNLOCK_PI,
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PTHREAD_ROBUST_MUTEX_PSHARED (mutex)),
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0, 0);
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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return ENOTRECOVERABLE;
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}
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if (robust)
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{
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ENQUEUE_MUTEX_PI (mutex);
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THREAD_SETMEM (THREAD_SELF, robust_head.list_op_pending, NULL);
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}
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mutex->__data.__owner = id;
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++mutex->__data.__nusers;
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mutex->__data.__count = 1;
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return 0;
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}
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case PTHREAD_MUTEX_PP_RECURSIVE_NP:
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case PTHREAD_MUTEX_PP_ERRORCHECK_NP:
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case PTHREAD_MUTEX_PP_NORMAL_NP:
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case PTHREAD_MUTEX_PP_ADAPTIVE_NP:
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{
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int kind = mutex->__data.__kind & PTHREAD_MUTEX_KIND_MASK_NP;
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oldval = mutex->__data.__lock;
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/* Check whether we already hold the mutex. */
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if (mutex->__data.__owner == id)
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{
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if (kind == PTHREAD_MUTEX_ERRORCHECK_NP)
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return EDEADLK;
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if (kind == PTHREAD_MUTEX_RECURSIVE_NP)
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{
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/* Just bump the counter. */
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if (__builtin_expect (mutex->__data.__count + 1 == 0, 0))
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/* Overflow of the counter. */
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return EAGAIN;
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++mutex->__data.__count;
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return 0;
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}
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}
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int oldprio = -1, ceilval;
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do
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{
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int ceiling = (oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK)
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>> PTHREAD_MUTEX_PRIO_CEILING_SHIFT;
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if (__pthread_current_priority () > ceiling)
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{
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if (oldprio != -1)
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__pthread_tpp_change_priority (oldprio, -1);
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return EINVAL;
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}
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int retval = __pthread_tpp_change_priority (oldprio, ceiling);
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if (retval)
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return retval;
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ceilval = ceiling << PTHREAD_MUTEX_PRIO_CEILING_SHIFT;
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oldprio = ceiling;
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oldval
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= atomic_compare_and_exchange_val_acq (&mutex->__data.__lock,
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ceilval | 1, ceilval);
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if (oldval == ceilval)
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break;
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}
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while ((oldval & PTHREAD_MUTEX_PRIO_CEILING_MASK) != ceilval);
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if (oldval != ceilval)
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{
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__pthread_tpp_change_priority (oldprio, -1);
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break;
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}
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assert (mutex->__data.__owner == 0);
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/* Record the ownership. */
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mutex->__data.__owner = id;
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++mutex->__data.__nusers;
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mutex->__data.__count = 1;
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return 0;
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}
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break;
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default:
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/* Correct code cannot set any other type. */
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return EINVAL;
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}
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return EBUSY;
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}
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#ifndef __pthread_mutex_trylock
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#ifndef pthread_mutex_trylock
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strong_alias (__pthread_mutex_trylock, pthread_mutex_trylock)
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#endif
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#endif
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