Merge "libc: remove global lock from recursive mutex implementation."
This commit is contained in:
commit
b118b9c5cd
@ -746,12 +746,6 @@ int pthread_setschedparam(pthread_t thid, int policy,
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}
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// mutex lock states
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//
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// 0: unlocked
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// 1: locked, no waiters
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// 2: locked, maybe waiters
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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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@ -762,21 +756,146 @@ int pthread_setschedparam(pthread_t thid, int policy,
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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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#define MUTEX_VALUE_OWNER(v) (((v) >> 16) & 0xffff)
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#define MUTEX_VALUE_COUNTER(v) (((v) >> 2) & 0xfff)
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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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#define MUTEX_OWNER(m) MUTEX_VALUE_OWNER((m)->value)
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#define MUTEX_COUNTER(m) MUTEX_VALUE_COUNTER((m)->value)
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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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* kernel TID of the owning thread. Note that this works because the Linux
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* kernel _only_ uses 16-bit values for thread ids.
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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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#define MUTEX_TYPE_MASK 0xc000
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#define MUTEX_TYPE_NORMAL 0x0000
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#define MUTEX_TYPE_RECURSIVE 0x4000
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#define MUTEX_TYPE_ERRORCHECK 0x8000
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#define MUTEX_COUNTER_SHIFT 2
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#define MUTEX_COUNTER_MASK 0x1ffc
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#define MUTEX_SHARED_MASK 0x2000
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/* a mutex attribute holds the following fields
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*
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@ -875,7 +994,7 @@ int pthread_mutex_init(pthread_mutex_t *mutex,
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return EINVAL;
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if (__likely(attr == NULL)) {
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mutex->value = MUTEX_TYPE_NORMAL;
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mutex->value = MUTEX_TYPE_BITS_NORMAL;
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return 0;
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}
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@ -884,13 +1003,13 @@ int pthread_mutex_init(pthread_mutex_t *mutex,
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switch (*attr & MUTEXATTR_TYPE_MASK) {
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case PTHREAD_MUTEX_NORMAL:
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value |= MUTEX_TYPE_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_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_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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@ -916,17 +1035,21 @@ int pthread_mutex_init(pthread_mutex_t *mutex,
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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 to 1. __bionic_cmpxchg() returns 0
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* if it made the swap successfully. If the result is nonzero, this
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* lock is already held by another thread.
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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(shared|0, shared|1, &mutex->value ) != 0) {
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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. We need to swap in the new
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* state value and then wait until somebody wakes us up.
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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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@ -939,8 +1062,8 @@ _normal_lock(pthread_mutex_t* mutex, int shared)
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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(shared|2, &mutex->value ) != (shared|0))
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__futex_wait_ex(&mutex->value, shared, shared|2, 0);
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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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@ -959,7 +1082,7 @@ _normal_unlock(pthread_mutex_t* mutex, int shared)
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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|1)) {
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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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@ -1001,20 +1124,6 @@ _normal_unlock(pthread_mutex_t* mutex, int shared)
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}
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}
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static pthread_mutex_t __recursive_lock = PTHREAD_MUTEX_INITIALIZER;
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static __inline__ void
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_recursive_lock(void)
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{
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_normal_lock(&__recursive_lock, 0);
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}
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static __inline__ void
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_recursive_unlock(void)
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{
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_normal_unlock(&__recursive_lock, 0);
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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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@ -1030,7 +1139,7 @@ _recursive_unlock(void)
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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_ERRORCHECK) {
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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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@ -1039,28 +1148,27 @@ _recursive_increment(pthread_mutex_t* mutex, int mvalue, int mtype)
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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 ((mvalue & MUTEX_COUNTER_MASK) == MUTEX_COUNTER_MASK) {
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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 the recursive global lock to do that.
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*
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* The lock/unlock sequence also provides a full memory barrier
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* so we don't need to add one here explicitely.
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* need to use an atomic cmpxchg loop to update the counter.
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*/
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_recursive_lock();
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/* increment counter, overflow was already checked */
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/* NOTE: we need to reload the value since its lower bits could have
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* been modified since the exit of _recursive_lock()
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*/
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mutex->value = mutex->value + (1 << MUTEX_COUNTER_SHIFT);
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_recursive_unlock();
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return 0;
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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 (__likely(__bionic_cmpxchg(mvalue, newval, &mutex->value) == 0)) {
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/* mutex is still locked, not need for a memory barrier */
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return 0;
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}
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/* the value was changed, this happens when another thread changes
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* the lower state bits from 1 to 2 to indicate contention. This
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* cannot change the counter, so simply reload and try again.
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*/
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mvalue = mutex->value;
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}
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}
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__LIBC_HIDDEN__
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@ -1076,53 +1184,72 @@ int pthread_mutex_lock_impl(pthread_mutex_t *mutex)
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shared = (mvalue & MUTEX_SHARED_MASK);
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/* Handle normal case first */
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if ( __likely(mtype == MUTEX_TYPE_NORMAL) ) {
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if ( __likely(mtype == MUTEX_TYPE_BITS_NORMAL) ) {
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_normal_lock(mutex, shared);
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return 0;
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}
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/* Do we already own this recursive or error-check mutex ? */
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tid = __get_thread()->kernel_id;
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if ( tid == MUTEX_VALUE_OWNER(mvalue) )
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if ( tid == MUTEX_OWNER_FROM_BITS(mvalue) )
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return _recursive_increment(mutex, mvalue, mtype);
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/* We don't own the mutex, so try to get it.
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*
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* First, we try to change its state from 0 to 1, if this
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* doesn't work, try to change it to state 2.
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*/
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new_lock_type = 1;
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/* compute futex wait opcode and restore shared flag in mtype */
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/* Add in shared state to avoid extra 'or' operations below */
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mtype |= shared;
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for (;;) {
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int oldv;
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_recursive_lock();
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oldv = mutex->value;
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if (oldv == mtype) { /* uncontended released lock => 1 or 2 */
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mutex->value = ((tid << 16) | mtype | new_lock_type);
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} else if ((oldv & 3) == 1) { /* locked state 1 => state 2 */
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oldv ^= 3;
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mutex->value = oldv;
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/* First, if the mutex is unlocked, try to quickly acquire it.
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* In the optimistic case where this works, set the state to 1 to
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* indicate locked with no contention */
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if (mvalue == mtype) {
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int newval = MUTEX_OWNER_TO_BITS(tid) | mtype | MUTEX_STATE_BITS_LOCKED_UNCONTENDED;
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if (__bionic_cmpxchg(mvalue, newval, &mutex->value) == 0) {
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ANDROID_MEMBAR_FULL();
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return 0;
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}
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_recursive_unlock();
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if (oldv == mtype)
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break;
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/*
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* The lock was held, possibly contended by others. From
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* now on, if we manage to acquire the lock, we have to
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* assume that others are still contending for it so that
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* we'll wake them when we unlock it.
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*/
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new_lock_type = 2;
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__futex_wait_ex(&mutex->value, shared, oldv, NULL);
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/* argh, the value changed, reload before entering the loop */
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mvalue = mutex->value;
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}
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return 0;
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for (;;) {
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int newval;
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/* if the mutex is unlocked, its value should be 'mtype' and
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* we try to acquire it by setting its owner and state atomically.
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* NOTE: We put the state to 2 since we _know_ there is contention
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* when we are in this loop. This ensures all waiters will be
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* unlocked.
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*/
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if (mvalue == mtype) {
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newval = MUTEX_OWNER_TO_BITS(tid) | mtype | MUTEX_STATE_BITS_LOCKED_CONTENDED;
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/* TODO: Change this to __bionic_cmpxchg_acquire when we
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* implement it to get rid of the explicit memory
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* barrier below.
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*/
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if (__unlikely(__bionic_cmpxchg(mvalue, newval, &mutex->value) != 0)) {
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mvalue = mutex->value;
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continue;
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}
|
||||
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 (__unlikely(__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)
|
||||
@ -1151,29 +1278,45 @@ int pthread_mutex_unlock_impl(pthread_mutex_t *mutex)
|
||||
shared = (mvalue & MUTEX_SHARED_MASK);
|
||||
|
||||
/* Handle common case first */
|
||||
if (__likely(mtype == MUTEX_TYPE_NORMAL)) {
|
||||
if (__likely(mtype == MUTEX_TYPE_BITS_NORMAL)) {
|
||||
_normal_unlock(mutex, shared);
|
||||
return 0;
|
||||
}
|
||||
|
||||
/* Do we already own this recursive or error-check mutex ? */
|
||||
tid = __get_thread()->kernel_id;
|
||||
if ( tid != MUTEX_VALUE_OWNER(mvalue) )
|
||||
if ( tid != MUTEX_OWNER_FROM_BITS(mvalue) )
|
||||
return EPERM;
|
||||
|
||||
/* We do, decrement counter or release the mutex if it is 0 */
|
||||
_recursive_lock();
|
||||
oldv = mutex->value;
|
||||
if (oldv & MUTEX_COUNTER_MASK) {
|
||||
mutex->value = oldv - (1 << MUTEX_COUNTER_SHIFT);
|
||||
oldv = 0;
|
||||
} else {
|
||||
mutex->value = shared | mtype;
|
||||
/* 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 (__likely(__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;
|
||||
}
|
||||
}
|
||||
_recursive_unlock();
|
||||
|
||||
/* 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 ((oldv & 3) == 2) {
|
||||
if (MUTEX_STATE_BITS_IS_LOCKED_CONTENDED(mvalue)) {
|
||||
__futex_wake_ex(&mutex->value, shared, 1);
|
||||
}
|
||||
return 0;
|
||||
@ -1202,9 +1345,11 @@ int pthread_mutex_trylock_impl(pthread_mutex_t *mutex)
|
||||
shared = (mvalue & MUTEX_SHARED_MASK);
|
||||
|
||||
/* Handle common case first */
|
||||
if ( __likely(mtype == MUTEX_TYPE_NORMAL) )
|
||||
if ( __likely(mtype == MUTEX_TYPE_BITS_NORMAL) )
|
||||
{
|
||||
if (__bionic_cmpxchg(shared|0, shared|1, &mutex->value) == 0) {
|
||||
if (__bionic_cmpxchg(shared|MUTEX_STATE_BITS_UNLOCKED,
|
||||
shared|MUTEX_STATE_BITS_LOCKED_UNCONTENDED,
|
||||
&mutex->value) == 0) {
|
||||
ANDROID_MEMBAR_FULL();
|
||||
return 0;
|
||||
}
|
||||
@ -1214,23 +1359,22 @@ int pthread_mutex_trylock_impl(pthread_mutex_t *mutex)
|
||||
|
||||
/* Do we already own this recursive or error-check mutex ? */
|
||||
tid = __get_thread()->kernel_id;
|
||||
if ( tid == MUTEX_VALUE_OWNER(mvalue) )
|
||||
if ( tid == MUTEX_OWNER_FROM_BITS(mvalue) )
|
||||
return _recursive_increment(mutex, mvalue, mtype);
|
||||
|
||||
/* Restore sharing bit in mtype */
|
||||
mtype |= shared;
|
||||
/* 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;
|
||||
|
||||
/* Try to lock it, just once. */
|
||||
_recursive_lock();
|
||||
oldv = mutex->value;
|
||||
if (oldv == mtype) /* uncontended released lock => state 1 */
|
||||
mutex->value = ((tid << 16) | mtype | 1);
|
||||
_recursive_unlock();
|
||||
if (__likely(__bionic_cmpxchg(mtype, mvalue, &mutex->value) == 0)) {
|
||||
ANDROID_MEMBAR_FULL();
|
||||
return 0;
|
||||
}
|
||||
|
||||
if (oldv != mtype)
|
||||
return EBUSY;
|
||||
|
||||
return 0;
|
||||
return EBUSY;
|
||||
}
|
||||
|
||||
int pthread_mutex_trylock(pthread_mutex_t *mutex)
|
||||
@ -1299,20 +1443,24 @@ int pthread_mutex_lock_timeout_np_impl(pthread_mutex_t *mutex, unsigned msecs)
|
||||
shared = (mvalue & MUTEX_SHARED_MASK);
|
||||
|
||||
/* Handle common case first */
|
||||
if ( __likely(mtype == MUTEX_TYPE_NORMAL) )
|
||||
if ( __likely(mtype == MUTEX_TYPE_BITS_NORMAL) )
|
||||
{
|
||||
/* fast path for uncontended lock */
|
||||
if (__bionic_cmpxchg(shared|0, shared|1, &mutex->value) == 0) {
|
||||
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(shared|2, &mutex->value) != (shared|0)) {
|
||||
while (__bionic_swap(locked_contended, &mutex->value) != unlocked) {
|
||||
if (__timespec_to_absolute(&ts, &abstime, clock) < 0)
|
||||
return EBUSY;
|
||||
|
||||
__futex_wait_ex(&mutex->value, shared, shared|2, &ts);
|
||||
__futex_wait_ex(&mutex->value, shared, locked_contended, &ts);
|
||||
}
|
||||
ANDROID_MEMBAR_FULL();
|
||||
return 0;
|
||||
@ -1320,50 +1468,75 @@ int pthread_mutex_lock_timeout_np_impl(pthread_mutex_t *mutex, unsigned msecs)
|
||||
|
||||
/* Do we already own this recursive or error-check mutex ? */
|
||||
tid = __get_thread()->kernel_id;
|
||||
if ( tid == MUTEX_VALUE_OWNER(mvalue) )
|
||||
if ( tid == MUTEX_OWNER_FROM_BITS(mvalue) )
|
||||
return _recursive_increment(mutex, mvalue, mtype);
|
||||
|
||||
/* We don't own the mutex, so try to get it.
|
||||
*
|
||||
* First, we try to change its state from 0 to 1, if this
|
||||
* doesn't work, try to change it to state 2.
|
||||
/* 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.
|
||||
*/
|
||||
new_lock_type = 1;
|
||||
mtype |= shared;
|
||||
|
||||
/* Compute wait op and restore sharing bit in mtype */
|
||||
mtype |= shared;
|
||||
/* first try a quick lock */
|
||||
if (mvalue == mtype) {
|
||||
mvalue = MUTEX_OWNER_TO_BITS(tid) | mtype | MUTEX_STATE_BITS_LOCKED_UNCONTENDED;
|
||||
if (__likely(__bionic_cmpxchg(mtype, mvalue, &mutex->value) == 0)) {
|
||||
ANDROID_MEMBAR_FULL();
|
||||
return 0;
|
||||
}
|
||||
mvalue = mutex->value;
|
||||
}
|
||||
|
||||
for (;;) {
|
||||
int oldv;
|
||||
struct timespec ts;
|
||||
struct timespec ts;
|
||||
|
||||
_recursive_lock();
|
||||
oldv = mutex->value;
|
||||
if (oldv == mtype) { /* uncontended released lock => 1 or 2 */
|
||||
mutex->value = ((tid << 16) | mtype | new_lock_type);
|
||||
} else if ((oldv & 3) == 1) { /* locked state 1 => state 2 */
|
||||
oldv ^= 3;
|
||||
mutex->value = oldv;
|
||||
/* 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;
|
||||
}
|
||||
_recursive_unlock();
|
||||
|
||||
if (oldv == mtype)
|
||||
break;
|
||||
|
||||
/*
|
||||
* The lock was held, possibly contended by others. From
|
||||
* now on, if we manage to acquire the lock, we have to
|
||||
* assume that others are still contending for it so that
|
||||
* we'll wake them when we unlock it.
|
||||
*/
|
||||
new_lock_type = 2;
|
||||
/* 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;
|
||||
|
||||
__futex_wait_ex(&mutex->value, shared, oldv, &ts);
|
||||
/* 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;
|
||||
}
|
||||
}
|
||||
return 0;
|
||||
/* NOTREACHED */
|
||||
}
|
||||
|
||||
int pthread_mutex_lock_timeout_np(pthread_mutex_t *mutex, unsigned msecs)
|
||||
|
Loading…
x
Reference in New Issue
Block a user