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