/* * Copyright (C) 2008 The Android Open Source Project * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. */ #include #include #include #include #include #include #include "pthread_internal.h" #include "private/bionic_atomic_inline.h" #include "private/bionic_futex.h" #include "private/bionic_tls.h" #include "private/thread_private.h" extern void pthread_debug_mutex_lock_check(pthread_mutex_t *mutex); extern void pthread_debug_mutex_unlock_check(pthread_mutex_t *mutex); /* a mutex is implemented as a 32-bit integer holding the following fields * * bits: name description * 31-16 tid owner thread's tid (recursive and errorcheck only) * 15-14 type mutex type * 13 shared process-shared flag * 12-2 counter counter of recursive mutexes * 1-0 state lock state (0, 1 or 2) */ /* Convenience macro, creates a mask of 'bits' bits that starts from * the 'shift'-th least significant bit in a 32-bit word. * * Examples: FIELD_MASK(0,4) -> 0xf * FIELD_MASK(16,9) -> 0x1ff0000 */ #define FIELD_MASK(shift,bits) (((1 << (bits))-1) << (shift)) /* This one is used to create a bit pattern from a given field value */ #define FIELD_TO_BITS(val,shift,bits) (((val) & ((1 << (bits))-1)) << (shift)) /* And this one does the opposite, i.e. extract a field's value from a bit pattern */ #define FIELD_FROM_BITS(val,shift,bits) (((val) >> (shift)) & ((1 << (bits))-1)) /* Mutex state: * * 0 for unlocked * 1 for locked, no waiters * 2 for locked, maybe waiters */ #define MUTEX_STATE_SHIFT 0 #define MUTEX_STATE_LEN 2 #define MUTEX_STATE_MASK FIELD_MASK(MUTEX_STATE_SHIFT, MUTEX_STATE_LEN) #define MUTEX_STATE_FROM_BITS(v) FIELD_FROM_BITS(v, MUTEX_STATE_SHIFT, MUTEX_STATE_LEN) #define MUTEX_STATE_TO_BITS(v) FIELD_TO_BITS(v, MUTEX_STATE_SHIFT, MUTEX_STATE_LEN) #define MUTEX_STATE_UNLOCKED 0 /* must be 0 to match __PTHREAD_MUTEX_INIT_VALUE */ #define MUTEX_STATE_LOCKED_UNCONTENDED 1 /* must be 1 due to atomic dec in unlock operation */ #define MUTEX_STATE_LOCKED_CONTENDED 2 /* must be 1 + LOCKED_UNCONTENDED due to atomic dec */ #define MUTEX_STATE_FROM_BITS(v) FIELD_FROM_BITS(v, MUTEX_STATE_SHIFT, MUTEX_STATE_LEN) #define MUTEX_STATE_TO_BITS(v) FIELD_TO_BITS(v, MUTEX_STATE_SHIFT, MUTEX_STATE_LEN) #define MUTEX_STATE_BITS_UNLOCKED MUTEX_STATE_TO_BITS(MUTEX_STATE_UNLOCKED) #define MUTEX_STATE_BITS_LOCKED_UNCONTENDED MUTEX_STATE_TO_BITS(MUTEX_STATE_LOCKED_UNCONTENDED) #define MUTEX_STATE_BITS_LOCKED_CONTENDED MUTEX_STATE_TO_BITS(MUTEX_STATE_LOCKED_CONTENDED) /* return true iff the mutex if locked with no waiters */ #define MUTEX_STATE_BITS_IS_LOCKED_UNCONTENDED(v) (((v) & MUTEX_STATE_MASK) == MUTEX_STATE_BITS_LOCKED_UNCONTENDED) /* return true iff the mutex if locked with maybe waiters */ #define MUTEX_STATE_BITS_IS_LOCKED_CONTENDED(v) (((v) & MUTEX_STATE_MASK) == MUTEX_STATE_BITS_LOCKED_CONTENDED) /* used to flip from LOCKED_UNCONTENDED to LOCKED_CONTENDED */ #define MUTEX_STATE_BITS_FLIP_CONTENTION(v) ((v) ^ (MUTEX_STATE_BITS_LOCKED_CONTENDED ^ MUTEX_STATE_BITS_LOCKED_UNCONTENDED)) /* Mutex counter: * * We need to check for overflow before incrementing, and we also need to * detect when the counter is 0 */ #define MUTEX_COUNTER_SHIFT 2 #define MUTEX_COUNTER_LEN 11 #define MUTEX_COUNTER_MASK FIELD_MASK(MUTEX_COUNTER_SHIFT, MUTEX_COUNTER_LEN) #define MUTEX_COUNTER_BITS_WILL_OVERFLOW(v) (((v) & MUTEX_COUNTER_MASK) == MUTEX_COUNTER_MASK) #define MUTEX_COUNTER_BITS_IS_ZERO(v) (((v) & MUTEX_COUNTER_MASK) == 0) /* Used to increment the counter directly after overflow has been checked */ #define MUTEX_COUNTER_BITS_ONE FIELD_TO_BITS(1,MUTEX_COUNTER_SHIFT,MUTEX_COUNTER_LEN) /* Returns true iff the counter is 0 */ #define MUTEX_COUNTER_BITS_ARE_ZERO(v) (((v) & MUTEX_COUNTER_MASK) == 0) /* Mutex shared bit flag * * This flag is set to indicate that the mutex is shared among processes. * This changes the futex opcode we use for futex wait/wake operations * (non-shared operations are much faster). */ #define MUTEX_SHARED_SHIFT 13 #define MUTEX_SHARED_MASK FIELD_MASK(MUTEX_SHARED_SHIFT,1) /* Mutex type: * * We support normal, recursive and errorcheck mutexes. * * The constants defined here *cannot* be changed because they must match * the C library ABI which defines the following initialization values in * : * * __PTHREAD_MUTEX_INIT_VALUE * __PTHREAD_RECURSIVE_MUTEX_VALUE * __PTHREAD_ERRORCHECK_MUTEX_INIT_VALUE */ #define MUTEX_TYPE_SHIFT 14 #define MUTEX_TYPE_LEN 2 #define MUTEX_TYPE_MASK FIELD_MASK(MUTEX_TYPE_SHIFT,MUTEX_TYPE_LEN) #define MUTEX_TYPE_NORMAL 0 /* Must be 0 to match __PTHREAD_MUTEX_INIT_VALUE */ #define MUTEX_TYPE_RECURSIVE 1 #define MUTEX_TYPE_ERRORCHECK 2 #define MUTEX_TYPE_TO_BITS(t) FIELD_TO_BITS(t, MUTEX_TYPE_SHIFT, MUTEX_TYPE_LEN) #define MUTEX_TYPE_BITS_NORMAL MUTEX_TYPE_TO_BITS(MUTEX_TYPE_NORMAL) #define MUTEX_TYPE_BITS_RECURSIVE MUTEX_TYPE_TO_BITS(MUTEX_TYPE_RECURSIVE) #define MUTEX_TYPE_BITS_ERRORCHECK MUTEX_TYPE_TO_BITS(MUTEX_TYPE_ERRORCHECK) /* Mutex owner field: * * This is only used for recursive and errorcheck mutexes. It holds the * tid of the owning thread. Note that this works because the Linux * kernel _only_ uses 16-bit values for tids. * * More specifically, it will wrap to 10000 when it reaches over 32768 for * application processes. You can check this by running the following inside * an adb shell session: * OLDPID=$$; while true; do NEWPID=$(sh -c 'echo $$') if [ "$NEWPID" -gt 32768 ]; then echo "AARGH: new PID $NEWPID is too high!" exit 1 fi if [ "$NEWPID" -lt "$OLDPID" ]; then echo "****** Wrapping from PID $OLDPID to $NEWPID. *******" else echo -n "$NEWPID!" fi OLDPID=$NEWPID done * Note that you can run the same example on a desktop Linux system, * the wrapping will also happen at 32768, but will go back to 300 instead. */ #define MUTEX_OWNER_SHIFT 16 #define MUTEX_OWNER_LEN 16 #define MUTEX_OWNER_FROM_BITS(v) FIELD_FROM_BITS(v,MUTEX_OWNER_SHIFT,MUTEX_OWNER_LEN) #define MUTEX_OWNER_TO_BITS(v) FIELD_TO_BITS(v,MUTEX_OWNER_SHIFT,MUTEX_OWNER_LEN) /* Convenience macros. * * These are used to form or modify the bit pattern of a given mutex value */ /* a mutex attribute holds the following fields * * bits: name description * 0-3 type type of mutex * 4 shared process-shared flag */ #define MUTEXATTR_TYPE_MASK 0x000f #define MUTEXATTR_SHARED_MASK 0x0010 int pthread_mutexattr_init(pthread_mutexattr_t *attr) { if (attr) { *attr = PTHREAD_MUTEX_DEFAULT; return 0; } else { return EINVAL; } } int pthread_mutexattr_destroy(pthread_mutexattr_t *attr) { if (attr) { *attr = -1; return 0; } else { return EINVAL; } } int pthread_mutexattr_gettype(const pthread_mutexattr_t *attr, int *type) { if (attr) { int atype = (*attr & MUTEXATTR_TYPE_MASK); if (atype >= PTHREAD_MUTEX_NORMAL && atype <= PTHREAD_MUTEX_ERRORCHECK) { *type = atype; return 0; } } return EINVAL; } int pthread_mutexattr_settype(pthread_mutexattr_t *attr, int type) { if (attr && type >= PTHREAD_MUTEX_NORMAL && type <= PTHREAD_MUTEX_ERRORCHECK ) { *attr = (*attr & ~MUTEXATTR_TYPE_MASK) | type; return 0; } return EINVAL; } /* process-shared mutexes are not supported at the moment */ int pthread_mutexattr_setpshared(pthread_mutexattr_t *attr, int pshared) { if (!attr) return EINVAL; switch (pshared) { case PTHREAD_PROCESS_PRIVATE: *attr &= ~MUTEXATTR_SHARED_MASK; return 0; case PTHREAD_PROCESS_SHARED: /* our current implementation of pthread actually supports shared * mutexes but won't cleanup if a process dies with the mutex held. * Nevertheless, it's better than nothing. Shared mutexes are used * by surfaceflinger and audioflinger. */ *attr |= MUTEXATTR_SHARED_MASK; return 0; } return EINVAL; } int pthread_mutexattr_getpshared(const pthread_mutexattr_t* attr, int* pshared) { if (!attr || !pshared) return EINVAL; *pshared = (*attr & MUTEXATTR_SHARED_MASK) ? PTHREAD_PROCESS_SHARED : PTHREAD_PROCESS_PRIVATE; return 0; } int pthread_mutex_init(pthread_mutex_t* mutex, const pthread_mutexattr_t* attr) { if (__predict_true(attr == NULL)) { mutex->value = MUTEX_TYPE_BITS_NORMAL; return 0; } int value = 0; if ((*attr & MUTEXATTR_SHARED_MASK) != 0) { value |= MUTEX_SHARED_MASK; } switch (*attr & MUTEXATTR_TYPE_MASK) { case PTHREAD_MUTEX_NORMAL: value |= MUTEX_TYPE_BITS_NORMAL; break; case PTHREAD_MUTEX_RECURSIVE: value |= MUTEX_TYPE_BITS_RECURSIVE; break; case PTHREAD_MUTEX_ERRORCHECK: value |= MUTEX_TYPE_BITS_ERRORCHECK; break; default: return EINVAL; } mutex->value = value; return 0; } /* * Lock a non-recursive mutex. * * As noted above, there are three states: * 0 (unlocked, no contention) * 1 (locked, no contention) * 2 (locked, contention) * * Non-recursive mutexes don't use the thread-id or counter fields, and the * "type" value is zero, so the only bits that will be set are the ones in * the lock state field. */ static __inline__ void _normal_lock(pthread_mutex_t* mutex, int shared) { /* convenience shortcuts */ const int unlocked = shared | MUTEX_STATE_BITS_UNLOCKED; const int locked_uncontended = shared | MUTEX_STATE_BITS_LOCKED_UNCONTENDED; /* * The common case is an unlocked mutex, so we begin by trying to * change the lock's state from 0 (UNLOCKED) to 1 (LOCKED). * __bionic_cmpxchg() returns 0 if it made the swap successfully. * If the result is nonzero, this lock is already held by another thread. */ if (__bionic_cmpxchg(unlocked, locked_uncontended, &mutex->value) != 0) { const int locked_contended = shared | MUTEX_STATE_BITS_LOCKED_CONTENDED; /* * We want to go to sleep until the mutex is available, which * requires promoting it to state 2 (CONTENDED). We need to * swap in the new state value and then wait until somebody wakes us up. * * __bionic_swap() returns the previous value. We swap 2 in and * see if we got zero back; if so, we have acquired the lock. If * not, another thread still holds the lock and we wait again. * * The second argument to the __futex_wait() call is compared * against the current value. If it doesn't match, __futex_wait() * returns immediately (otherwise, it sleeps for a time specified * by the third argument; 0 means sleep forever). This ensures * that the mutex is in state 2 when we go to sleep on it, which * guarantees a wake-up call. */ while (__bionic_swap(locked_contended, &mutex->value) != unlocked) __futex_wait_ex(&mutex->value, shared, locked_contended, 0); } ANDROID_MEMBAR_FULL(); } /* * Release a non-recursive mutex. The caller is responsible for determining * that we are in fact the owner of this lock. */ static __inline__ void _normal_unlock(pthread_mutex_t* mutex, int shared) { ANDROID_MEMBAR_FULL(); /* * The mutex state will be 1 or (rarely) 2. We use an atomic decrement * to release the lock. __bionic_atomic_dec() returns the previous value; * if it wasn't 1 we have to do some additional work. */ if (__bionic_atomic_dec(&mutex->value) != (shared|MUTEX_STATE_BITS_LOCKED_UNCONTENDED)) { /* * Start by releasing the lock. The decrement changed it from * "contended lock" to "uncontended lock", which means we still * hold it, and anybody who tries to sneak in will push it back * to state 2. * * Once we set it to zero the lock is up for grabs. We follow * this with a __futex_wake() to ensure that one of the waiting * threads has a chance to grab it. * * This doesn't cause a race with the swap/wait pair in * _normal_lock(), because the __futex_wait() call there will * return immediately if the mutex value isn't 2. */ mutex->value = shared; /* * Wake up one waiting thread. We don't know which thread will be * woken or when it'll start executing -- futexes make no guarantees * here. There may not even be a thread waiting. * * The newly-woken thread will replace the 0 we just set above * with 2, which means that when it eventually releases the mutex * it will also call FUTEX_WAKE. This results in one extra wake * call whenever a lock is contended, but lets us avoid forgetting * anyone without requiring us to track the number of sleepers. * * It's possible for another thread to sneak in and grab the lock * between the zero assignment above and the wake call below. If * the new thread is "slow" and holds the lock for a while, we'll * wake up a sleeper, which will swap in a 2 and then go back to * sleep since the lock is still held. If the new thread is "fast", * running to completion before we call wake, the thread we * eventually wake will find an unlocked mutex and will execute. * Either way we have correct behavior and nobody is orphaned on * the wait queue. */ __futex_wake_ex(&mutex->value, shared, 1); } } /* This common inlined function is used to increment the counter of an * errorcheck or recursive mutex. * * For errorcheck mutexes, it will return EDEADLK * If the counter overflows, it will return EAGAIN * Otherwise, it atomically increments the counter and returns 0 * after providing an acquire barrier. * * mtype is the current mutex type * mvalue is the current mutex value (already loaded) * mutex pointers to the mutex. */ static __inline__ __attribute__((always_inline)) int _recursive_increment(pthread_mutex_t* mutex, int mvalue, int mtype) { if (mtype == MUTEX_TYPE_BITS_ERRORCHECK) { /* trying to re-lock a mutex we already acquired */ return EDEADLK; } /* Detect recursive lock overflow and return EAGAIN. * This is safe because only the owner thread can modify the * counter bits in the mutex value. */ if (MUTEX_COUNTER_BITS_WILL_OVERFLOW(mvalue)) { return EAGAIN; } /* We own the mutex, but other threads are able to change * the lower bits (e.g. promoting it to "contended"), so we * need to use an atomic cmpxchg loop to update the counter. */ for (;;) { /* increment counter, overflow was already checked */ int newval = mvalue + MUTEX_COUNTER_BITS_ONE; if (__predict_true(__bionic_cmpxchg(mvalue, newval, &mutex->value) == 0)) { /* mutex is still locked, not need for a memory barrier */ return 0; } /* the value was changed, this happens when another thread changes * the lower state bits from 1 to 2 to indicate contention. This * cannot change the counter, so simply reload and try again. */ mvalue = mutex->value; } } __LIBC_HIDDEN__ int pthread_mutex_lock_impl(pthread_mutex_t *mutex) { int mvalue, mtype, tid, shared; mvalue = mutex->value; mtype = (mvalue & MUTEX_TYPE_MASK); shared = (mvalue & MUTEX_SHARED_MASK); /* Handle normal case first */ if ( __predict_true(mtype == MUTEX_TYPE_BITS_NORMAL) ) { _normal_lock(mutex, shared); return 0; } /* Do we already own this recursive or error-check mutex ? */ tid = __get_thread()->tid; if ( tid == MUTEX_OWNER_FROM_BITS(mvalue) ) return _recursive_increment(mutex, mvalue, mtype); /* Add in shared state to avoid extra 'or' operations below */ mtype |= shared; /* First, if the mutex is unlocked, try to quickly acquire it. * In the optimistic case where this works, set the state to 1 to * indicate locked with no contention */ if (mvalue == mtype) { int newval = MUTEX_OWNER_TO_BITS(tid) | mtype | MUTEX_STATE_BITS_LOCKED_UNCONTENDED; if (__bionic_cmpxchg(mvalue, newval, &mutex->value) == 0) { ANDROID_MEMBAR_FULL(); return 0; } /* argh, the value changed, reload before entering the loop */ mvalue = mutex->value; } for (;;) { int newval; /* if the mutex is unlocked, its value should be 'mtype' and * we try to acquire it by setting its owner and state atomically. * NOTE: We put the state to 2 since we _know_ there is contention * when we are in this loop. This ensures all waiters will be * unlocked. */ if (mvalue == mtype) { newval = MUTEX_OWNER_TO_BITS(tid) | mtype | MUTEX_STATE_BITS_LOCKED_CONTENDED; /* TODO: Change this to __bionic_cmpxchg_acquire when we * implement it to get rid of the explicit memory * barrier below. */ if (__predict_false(__bionic_cmpxchg(mvalue, newval, &mutex->value) != 0)) { mvalue = mutex->value; continue; } ANDROID_MEMBAR_FULL(); return 0; } /* the mutex is already locked by another thread, if its state is 1 * we will change it to 2 to indicate contention. */ if (MUTEX_STATE_BITS_IS_LOCKED_UNCONTENDED(mvalue)) { newval = MUTEX_STATE_BITS_FLIP_CONTENTION(mvalue); /* locked state 1 => state 2 */ if (__predict_false(__bionic_cmpxchg(mvalue, newval, &mutex->value) != 0)) { mvalue = mutex->value; continue; } mvalue = newval; } /* wait until the mutex is unlocked */ __futex_wait_ex(&mutex->value, shared, mvalue, NULL); mvalue = mutex->value; } /* NOTREACHED */ } int pthread_mutex_lock(pthread_mutex_t *mutex) { int err = pthread_mutex_lock_impl(mutex); if (PTHREAD_DEBUG_ENABLED) { if (!err) { pthread_debug_mutex_lock_check(mutex); } } return err; } __LIBC_HIDDEN__ int pthread_mutex_unlock_impl(pthread_mutex_t *mutex) { int mvalue, mtype, tid, shared; mvalue = mutex->value; mtype = (mvalue & MUTEX_TYPE_MASK); shared = (mvalue & MUTEX_SHARED_MASK); /* Handle common case first */ if (__predict_true(mtype == MUTEX_TYPE_BITS_NORMAL)) { _normal_unlock(mutex, shared); return 0; } /* Do we already own this recursive or error-check mutex ? */ tid = __get_thread()->tid; if ( tid != MUTEX_OWNER_FROM_BITS(mvalue) ) return EPERM; /* If the counter is > 0, we can simply decrement it atomically. * Since other threads can mutate the lower state bits (and only the * lower state bits), use a cmpxchg to do it. */ if (!MUTEX_COUNTER_BITS_IS_ZERO(mvalue)) { for (;;) { int newval = mvalue - MUTEX_COUNTER_BITS_ONE; if (__predict_true(__bionic_cmpxchg(mvalue, newval, &mutex->value) == 0)) { /* success: we still own the mutex, so no memory barrier */ return 0; } /* the value changed, so reload and loop */ mvalue = mutex->value; } } /* the counter is 0, so we're going to unlock the mutex by resetting * its value to 'unlocked'. We need to perform a swap in order * to read the current state, which will be 2 if there are waiters * to awake. * * TODO: Change this to __bionic_swap_release when we implement it * to get rid of the explicit memory barrier below. */ ANDROID_MEMBAR_FULL(); /* RELEASE BARRIER */ mvalue = __bionic_swap(mtype | shared | MUTEX_STATE_BITS_UNLOCKED, &mutex->value); /* Wake one waiting thread, if any */ if (MUTEX_STATE_BITS_IS_LOCKED_CONTENDED(mvalue)) { __futex_wake_ex(&mutex->value, shared, 1); } return 0; } int pthread_mutex_unlock(pthread_mutex_t *mutex) { if (PTHREAD_DEBUG_ENABLED) { pthread_debug_mutex_unlock_check(mutex); } return pthread_mutex_unlock_impl(mutex); } __LIBC_HIDDEN__ int pthread_mutex_trylock_impl(pthread_mutex_t *mutex) { int mvalue, mtype, tid, shared; mvalue = mutex->value; mtype = (mvalue & MUTEX_TYPE_MASK); shared = (mvalue & MUTEX_SHARED_MASK); /* Handle common case first */ if ( __predict_true(mtype == MUTEX_TYPE_BITS_NORMAL) ) { if (__bionic_cmpxchg(shared|MUTEX_STATE_BITS_UNLOCKED, shared|MUTEX_STATE_BITS_LOCKED_UNCONTENDED, &mutex->value) == 0) { ANDROID_MEMBAR_FULL(); return 0; } return EBUSY; } /* Do we already own this recursive or error-check mutex ? */ tid = __get_thread()->tid; if ( tid == MUTEX_OWNER_FROM_BITS(mvalue) ) return _recursive_increment(mutex, mvalue, mtype); /* Same as pthread_mutex_lock, except that we don't want to wait, and * the only operation that can succeed is a single cmpxchg to acquire the * lock if it is released / not owned by anyone. No need for a complex loop. */ mtype |= shared | MUTEX_STATE_BITS_UNLOCKED; mvalue = MUTEX_OWNER_TO_BITS(tid) | mtype | MUTEX_STATE_BITS_LOCKED_UNCONTENDED; if (__predict_true(__bionic_cmpxchg(mtype, mvalue, &mutex->value) == 0)) { ANDROID_MEMBAR_FULL(); return 0; } return EBUSY; } int pthread_mutex_trylock(pthread_mutex_t *mutex) { int err = pthread_mutex_trylock_impl(mutex); if (PTHREAD_DEBUG_ENABLED) { if (!err) { pthread_debug_mutex_lock_check(mutex); } } return err; } /* initialize 'abstime' to the current time according to 'clock' plus 'msecs' * milliseconds. */ static void __timespec_to_relative_msec(timespec* abstime, unsigned msecs, clockid_t clock) { clock_gettime(clock, abstime); abstime->tv_sec += msecs/1000; abstime->tv_nsec += (msecs%1000)*1000000; if (abstime->tv_nsec >= 1000000000) { abstime->tv_sec++; abstime->tv_nsec -= 1000000000; } } __LIBC_HIDDEN__ int pthread_mutex_lock_timeout_np_impl(pthread_mutex_t *mutex, unsigned msecs) { clockid_t clock = CLOCK_MONOTONIC; timespec abstime; timespec ts; int mvalue, mtype, tid, shared; /* compute absolute expiration time */ __timespec_to_relative_msec(&abstime, msecs, clock); mvalue = mutex->value; mtype = (mvalue & MUTEX_TYPE_MASK); shared = (mvalue & MUTEX_SHARED_MASK); /* Handle common case first */ if ( __predict_true(mtype == MUTEX_TYPE_BITS_NORMAL) ) { const int unlocked = shared | MUTEX_STATE_BITS_UNLOCKED; const int locked_uncontended = shared | MUTEX_STATE_BITS_LOCKED_UNCONTENDED; const int locked_contended = shared | MUTEX_STATE_BITS_LOCKED_CONTENDED; /* fast path for uncontended lock. Note: MUTEX_TYPE_BITS_NORMAL is 0 */ if (__bionic_cmpxchg(unlocked, locked_uncontended, &mutex->value) == 0) { ANDROID_MEMBAR_FULL(); return 0; } /* loop while needed */ while (__bionic_swap(locked_contended, &mutex->value) != unlocked) { if (__timespec_to_absolute(&ts, &abstime, clock) < 0) return EBUSY; __futex_wait_ex(&mutex->value, shared, locked_contended, &ts); } ANDROID_MEMBAR_FULL(); return 0; } /* Do we already own this recursive or error-check mutex ? */ tid = __get_thread()->tid; if ( tid == MUTEX_OWNER_FROM_BITS(mvalue) ) return _recursive_increment(mutex, mvalue, mtype); /* the following implements the same loop than pthread_mutex_lock_impl * but adds checks to ensure that the operation never exceeds the * absolute expiration time. */ mtype |= shared; /* first try a quick lock */ if (mvalue == mtype) { mvalue = MUTEX_OWNER_TO_BITS(tid) | mtype | MUTEX_STATE_BITS_LOCKED_UNCONTENDED; if (__predict_true(__bionic_cmpxchg(mtype, mvalue, &mutex->value) == 0)) { ANDROID_MEMBAR_FULL(); return 0; } mvalue = mutex->value; } for (;;) { timespec ts; /* if the value is 'unlocked', try to acquire it directly */ /* NOTE: put state to 2 since we know there is contention */ if (mvalue == mtype) /* unlocked */ { mvalue = MUTEX_OWNER_TO_BITS(tid) | mtype | MUTEX_STATE_BITS_LOCKED_CONTENDED; if (__bionic_cmpxchg(mtype, mvalue, &mutex->value) == 0) { ANDROID_MEMBAR_FULL(); return 0; } /* the value changed before we could lock it. We need to check * the time to avoid livelocks, reload the value, then loop again. */ if (__timespec_to_absolute(&ts, &abstime, clock) < 0) return EBUSY; mvalue = mutex->value; continue; } /* The value is locked. If 'uncontended', try to switch its state * to 'contented' to ensure we get woken up later. */ if (MUTEX_STATE_BITS_IS_LOCKED_UNCONTENDED(mvalue)) { int newval = MUTEX_STATE_BITS_FLIP_CONTENTION(mvalue); if (__bionic_cmpxchg(mvalue, newval, &mutex->value) != 0) { /* this failed because the value changed, reload it */ mvalue = mutex->value; } else { /* this succeeded, update mvalue */ mvalue = newval; } } /* check time and update 'ts' */ if (__timespec_to_absolute(&ts, &abstime, clock) < 0) return EBUSY; /* Only wait to be woken up if the state is '2', otherwise we'll * simply loop right now. This can happen when the second cmpxchg * in our loop failed because the mutex was unlocked by another * thread. */ if (MUTEX_STATE_BITS_IS_LOCKED_CONTENDED(mvalue)) { if (__futex_wait_ex(&mutex->value, shared, mvalue, &ts) == -ETIMEDOUT) { return EBUSY; } mvalue = mutex->value; } } /* NOTREACHED */ } int pthread_mutex_lock_timeout_np(pthread_mutex_t *mutex, unsigned msecs) { int err = pthread_mutex_lock_timeout_np_impl(mutex, msecs); if (PTHREAD_DEBUG_ENABLED) { if (!err) { pthread_debug_mutex_lock_check(mutex); } } return err; } int pthread_mutex_destroy(pthread_mutex_t *mutex) { int ret; /* use trylock to ensure that the mutex value is * valid and is not already locked. */ ret = pthread_mutex_trylock_impl(mutex); if (ret != 0) return ret; mutex->value = 0xdead10cc; return 0; }