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bionic: pthread: use private futexes by default for mutexes and condvars

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Private futexes are a recent kernel addition: faster futexes that cannot be
shared between processes. This patch uses them by default, unless the PROCESS_SHARED
attribute flag is used when creating a mutex and/or conditional variable.

Also introduces pthread_condattr_init/destroy/setpshared/getpshared.

Change-Id: I3a0e2116f467072b046524cb5babc00e41057a53
This commit is contained in:
David 'Digit' Turner
2010-03-10 16:44:08 -08:00
parent 1cfbda826c
commit ba9c6f0989
6 changed files with 612 additions and 299 deletions
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48
libc/arch-arm/bionic/atomics_arm.S
View File

@@ -43,6 +43,19 @@
#define FUTEX_WAIT 0
#define FUTEX_WAKE 1
/* Private futexes belong to a single address space and cannot be
* shared among processes. They are however significantly faster to
* operate than standard futexes.
*/
.global __futex_wait_private
.type __futex_wait_private, %function
.global __futex_wake_private
.type __futex_wake_private, %function
#define FUTEX_PRIVATE_FLAG 128
#define FUTEX_WAIT_PRIVATE (FUTEX_WAIT|FUTEX_PRIVATE_FLAG)
#define FUTEX_WAKE_PRIVATE (FUTEX_WAKE|FUTEX_PRIVATE_FLAG)
#if 1
.equ kernel_cmpxchg, 0xFFFF0FC0
.equ kernel_atomic_base, 0xFFFF0FFF
@@ -185,6 +198,28 @@ __futex_wake:
ldmia sp!, {r4, r7}
bx lr
__futex_wait_private:
.fnstart
stmdb sp!, {r4, r7}
.save {r4, r7}
mov r3, r2
mov r2, r1
mov r1, #FUTEX_WAIT_PRIVATE
ldr r7, =__NR_futex
swi #0
ldmia sp!, {r4, r7}
bx lr
.fnend
__futex_wake_private:
stmdb sp!, {r4, r7}
mov r2, r1
mov r1, #FUTEX_WAKE_PRIVATE
ldr r7, =__NR_futex
swi #0
ldmia sp!, {r4, r7}
bx lr
#else
__futex_wait:
@@ -200,4 +235,17 @@ __futex_wake:
swi #__NR_futex
bx lr
__futex_wait_private:
mov r3, r2
mov r2, r1
mov r1, #FUTEX_WAIT_PRIVATE
swi #__NR_futex
bx lr
__futex_wake_private:
mov r2, r1
mov r1, #FUTEX_WAKE_PRIVATE
swi #__NR_futex
bx lr
#endif

18
libc/arch-sh/bionic/atomics_sh.c
View File

@@ -98,3 +98,21 @@ int __futex_wake(volatile void *ftx, int count)
{
return futex(ftx, FUTEX_WAKE, count, NULL, NULL, 0);
}
/* Private futexes belong to a single address space and cannot be
* shared among processes. They are however significantly faster to
* operate than standard futexes.
*/
#define FUTEX_PRIVATE_FLAG 128
#define FUTEX_WAIT_PRIVATE (FUTEX_WAIT|FUTEX_PRIVATE_FLAG)
#define FUTEX_WAKE_PRIVATE (FUTEX_WAKE|FUTEX_PRIVATE_FLAG)
int __futex_wait_private(volatile void *ftx, int val, const struct timespec *timeout)
{
return futex(ftx, FUTEX_WAIT_PRIVATE, val, (void *)timeout, NULL, 0);
}
int __futex_wake_private(volatile void *ftx, int count)
{
return futex(ftx, FUTEX_WAKE_PRIVATE, count, NULL, NULL, 0);
}

37
libc/arch-x86/bionic/atomics_x86.c
View File

@@ -60,6 +60,43 @@ int __futex_wake(volatile void *ftx, int count)
return ret;
}
/* Private futexes belong to a single address space and cannot be
* shared among processes. They are however significantly faster to
* operate than standard futexes.
*/
#define FUTEX_PRIVATE_FLAG 128
#define FUTEX_WAIT_PRIVATE (FUTEX_WAIT|FUTEX_PRIVATE_FLAG)
#define FUTEX_WAKE_PRIVATE (FUTEX_WAKE|FUTEX_PRIVATE_FLAG)
int __futex_wait_private(volatile void *ftx, int val)
{
int ret;
asm volatile (
"int $0x80;"
: "=a" (ret)
: "0" (FUTEX_SYSCALL),
"b" (ftx),
"c" (FUTEX_WAIT_PRIVATE),
"d" (val),
"S" (0)
);
return ret;
}
int __futex_wake_private(volatile void *ftx, int count)
{
int ret;
asm volatile (
"int $0x80;"
: "=a" (ret)
: "0" (FUTEX_SYSCALL),
"b" (ftx),
"c" (FUTEX_WAKE_PRIVATE),
"d" (count)
);
return ret;
}
int __atomic_cmpxchg(int old, int new, volatile int* addr) {
int xchg;
asm volatile (

793
libc/bionic/pthread.c
View File

@@ -44,6 +44,9 @@
#include <assert.h>
#include <malloc.h>
#define __likely(cond) __builtin_expect(!!(cond), 1)
#define __unlikely(cond) __builtin_expect(!!(cond), 0)
extern int __pthread_clone(int (*fn)(void*), void *child_stack, int flags, void *arg);
extern void _exit_with_stack_teardown(void * stackBase, int stackSize, int retCode);
extern void _exit_thread(int retCode);
@@ -712,6 +715,9 @@ int pthread_setschedparam(pthread_t thid, int policy,
int __futex_wait(volatile void *ftx, int val, const struct timespec *timeout);
int __futex_wake(volatile void *ftx, int count);
int __futex_wait_private(volatile void *ftx, int val, const struct timespec *timeout);
int __futex_wake_private(volatile void *ftx, int count);
// mutex lock states
//
// 0: unlocked
@@ -723,7 +729,8 @@ int __futex_wake(volatile void *ftx, int count);
* bits: name description
* 31-16 tid owner thread's kernel id (recursive and errorcheck only)
* 15-14 type mutex type
* 13-2 counter counter of recursive mutexes
* 13 sharing sharing flag
* 12-2 counter counter of recursive mutexes
* 1-0 state lock state (0, 1 or 2)
*/
@@ -737,10 +744,21 @@ int __futex_wake(volatile void *ftx, int count);
#define MUTEX_TYPE_ERRORCHECK 0x8000
#define MUTEX_COUNTER_SHIFT 2
#define MUTEX_COUNTER_MASK 0x3ffc
#define MUTEX_COUNTER_MASK 0x1ffc
#define MUTEX_SHARING_MASK 0x2000
#define MUTEX_IS_SHARED(m) (((m)->value & MUTEX_SHARING_MASK) != 0)
/* A mutex attribute stores the following in its fields:
*
* bits: name description
* 0-3 type type of thread (NORMAL/RECURSIVE/ERRORCHECK)
* 4 sharing 1 if shared, or 0 otherwise.
*/
#define MUTEXATTR_TYPE_MASK 0x0007
#define MUTEXATTR_SHARING_MASK 0x0010
int pthread_mutexattr_init(pthread_mutexattr_t *attr)
{
@@ -764,10 +782,12 @@ int pthread_mutexattr_destroy(pthread_mutexattr_t *attr)
int pthread_mutexattr_gettype(const pthread_mutexattr_t *attr, int *type)
{
if (attr && *attr >= PTHREAD_MUTEX_NORMAL &&
*attr <= PTHREAD_MUTEX_ERRORCHECK ) {
*type = *attr;
return 0;
if (attr) {
int atype = (*attr & MUTEXATTR_TYPE_MASK);
if (atype >= PTHREAD_MUTEX_NORMAL && atype <= PTHREAD_MUTEX_ERRORCHECK) {
*type = atype;
return 0;
}
}
return EINVAL;
}
@@ -776,7 +796,7 @@ int pthread_mutexattr_settype(pthread_mutexattr_t *attr, int type)
{
if (attr && type >= PTHREAD_MUTEX_NORMAL &&
type <= PTHREAD_MUTEX_ERRORCHECK ) {
*attr = type;
*attr = (*attr & ~MUTEXATTR_TYPE_MASK) | type;
return 0;
}
return EINVAL;
@@ -791,54 +811,70 @@ int pthread_mutexattr_setpshared(pthread_mutexattr_t *attr, int pshared)
switch (pshared) {
case PTHREAD_PROCESS_PRIVATE:
*attr &= ~MUTEXATTR_SHARING_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_SHARING_MASK;
return 0;
}
return ENOTSUP;
return EINVAL;
}
int pthread_mutexattr_getpshared(pthread_mutexattr_t *attr, int *pshared)
{
if (!attr)
if (!attr || !pshared)
return EINVAL;
*pshared = PTHREAD_PROCESS_PRIVATE;
*pshared = (*attr & MUTEXATTR_SHARING_MASK) ? PTHREAD_PROCESS_SHARED
: PTHREAD_PROCESS_PRIVATE;
return 0;
}
int pthread_mutex_init(pthread_mutex_t *mutex,
const pthread_mutexattr_t *attr)
{
if ( mutex ) {
if (attr == NULL) {
mutex->value = MUTEX_TYPE_NORMAL;
return 0;
}
switch ( *attr ) {
case PTHREAD_MUTEX_NORMAL:
mutex->value = MUTEX_TYPE_NORMAL;
return 0;
int value = 0;
case PTHREAD_MUTEX_RECURSIVE:
mutex->value = MUTEX_TYPE_RECURSIVE;
return 0;
if (__unlikely(mutex == NULL))
return EINVAL;
case PTHREAD_MUTEX_ERRORCHECK:
mutex->value = MUTEX_TYPE_ERRORCHECK;
return 0;
}
if (__likely(attr == NULL)) {
mutex->value = MUTEX_TYPE_NORMAL;
return 0;
}
return EINVAL;
if ((*attr & MUTEXATTR_SHARING_MASK) != 0)
value |= MUTEX_SHARING_MASK;
switch (*attr & MUTEXATTR_TYPE_MASK) {
case PTHREAD_MUTEX_NORMAL:
value |= MUTEX_TYPE_NORMAL;
break;
case PTHREAD_MUTEX_RECURSIVE:
value |= MUTEX_TYPE_RECURSIVE;
break;
case PTHREAD_MUTEX_ERRORCHECK:
value |= MUTEX_TYPE_ERRORCHECK;
break;
default:
return EINVAL;
}
mutex->value = value;
return 0;
}
int pthread_mutex_destroy(pthread_mutex_t *mutex)
{
if (__unlikely(mutex == NULL))
return EINVAL;
mutex->value = 0xdead10cc;
return 0;
}
@@ -855,35 +891,46 @@ int pthread_mutex_destroy(pthread_mutex_t *mutex)
* 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.
*
* This routine is used for both shared and private mutexes.
*/
static __inline__ void
_normal_lock(pthread_mutex_t* mutex)
{
/*
* The common case is an unlocked mutex, so we begin by trying to
* change the lock's state from 0 to 1. __atomic_cmpxchg() returns 0
* if it made the swap successfully. If the result is nonzero, this
* lock is already held by another thread.
*/
if (__atomic_cmpxchg(0, 1, &mutex->value ) != 0) {
if (__likely(!MUTEX_IS_SHARED(mutex))) {
/*
* We want to go to sleep until the mutex is available, which
* requires promoting it to state 2. We need to swap in the new
* state value and then wait until somebody wakes us up.
*
* __atomic_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 (__atomic_swap(2, &mutex->value ) != 0)
__futex_wait(&mutex->value, 2, 0);
* The common case is an unlocked mutex, so we begin by trying to
* change the lock's state from 0 to 1. __atomic_cmpxchg() returns 0
* if it made the swap successfully. If the result is nonzero, this
* lock is already held by another thread.
*/
if (__atomic_cmpxchg(0, 1, &mutex->value) != 0) {
/*
* We want to go to sleep until the mutex is available, which
* requires promoting it to state 2. We need to swap in the new
* state value and then wait until somebody wakes us up.
*
* __atomic_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 (__atomic_swap(2, &mutex->value ) != 0)
__futex_wait_private(&mutex->value, 2, 0);
}
} else {
/* Same algorithm, with the sharing bit flag set */
const int sharing = MUTEX_SHARING_MASK;
if (__atomic_cmpxchg(sharing|0, sharing|1, &mutex->value) != 0) {
while (__atomic_swap(sharing|2, &mutex->value ) != (sharing|0))
__futex_wait(&mutex->value, sharing|2, 0);
}
}
}
@@ -894,50 +941,59 @@ _normal_lock(pthread_mutex_t* mutex)
static __inline__ void
_normal_unlock(pthread_mutex_t* mutex)
{
/*
* The mutex value will be 1 or (rarely) 2. We use an atomic decrement
* to release the lock. __atomic_dec() returns the previous value;
* if it wasn't 1 we have to do some additional work.
*/
if (__atomic_dec(&mutex->value) != 1) {
if (__likely(!MUTEX_IS_SHARED(mutex))) {
/*
* 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 = 0;
* The mutex value will be 1 or (rarely) 2. We use an atomic decrement
* to release the lock. __atomic_dec() returns the previous value;
* if it wasn't 1 we have to do some additional work.
*/
if (__atomic_dec(&mutex->value) != 1) {
/*
* 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 = 0;
/*
* 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(&mutex->value, 1);
/*
* 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_private(&mutex->value, 1);
}
} else {
/* Same algorithm with sharing bit flag set */
const int sharing = MUTEX_SHARING_MASK;
if (__atomic_dec(&mutex->value) != (sharing|1)) {
mutex->value = sharing;
__futex_wake(&mutex->value, 1);
}
}
}
@@ -955,173 +1011,200 @@ _recursive_unlock(void)
_normal_unlock( &__recursive_lock );
}
#define __likely(cond) __builtin_expect(!!(cond), 1)
#define __unlikely(cond) __builtin_expect(!!(cond), 0)
int pthread_mutex_lock(pthread_mutex_t *mutex)
{
if (__likely(mutex != NULL))
{
int mtype = (mutex->value & MUTEX_TYPE_MASK);
int mtype, tid, new_lock_type, sharing;
if ( __likely(mtype == MUTEX_TYPE_NORMAL) ) {
_normal_lock(mutex);
}
else
{
int tid = __get_thread()->kernel_id;
if (__unlikely(mutex == NULL))
return EINVAL;
if ( tid == MUTEX_OWNER(mutex) )
{
int oldv, counter;
/* get mutex type */
mtype = (mutex->value & MUTEX_TYPE_MASK);
if (mtype == MUTEX_TYPE_ERRORCHECK) {
/* trying to re-lock a mutex we already acquired */
return EDEADLK;
}
/*
* We own the mutex, but other threads are able to change
* the contents (e.g. promoting it to "contended"), so we
* need to hold the global lock.
*/
_recursive_lock();
oldv = mutex->value;
counter = (oldv + (1 << MUTEX_COUNTER_SHIFT)) & MUTEX_COUNTER_MASK;
mutex->value = (oldv & ~MUTEX_COUNTER_MASK) | counter;
_recursive_unlock();
}
else
{
/*
* If the new lock is available immediately, we grab it in
* the "uncontended" state.
*/
int new_lock_type = 1;
for (;;) {
int oldv;
_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;
}
_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;
__futex_wait( &mutex->value, oldv, 0 );
}
}
}
/* Handle normal mutexes quickly */
if ( __likely(mtype == MUTEX_TYPE_NORMAL) ) {
_normal_lock(mutex);
return 0;
}
return EINVAL;
/* This is a recursive or error check mutex.
* Check that we don't already own it.
*/
tid = __get_thread()->kernel_id;
if ( tid == MUTEX_OWNER(mutex) )
{
int oldv, counter;
if (mtype == MUTEX_TYPE_ERRORCHECK) {
/* trying to re-lock a mutex we already acquired */
return EDEADLK;
}
/*
* We own the mutex, but other threads are able to change
* the contents (e.g. promoting it to "contended"), so we
* need to hold the global lock.
*/
_recursive_lock();
oldv = mutex->value;
counter = (oldv + (1 << MUTEX_COUNTER_SHIFT)) & MUTEX_COUNTER_MASK;
mutex->value = (oldv & ~MUTEX_COUNTER_MASK) | counter;
_recursive_unlock();
return 0;
}
/* We don't own it, try to lock it.
* If the new lock is available immediately, we grab it in
* the "uncontended" state.
*/
new_lock_type = 1;
sharing = (mutex->value & MUTEX_SHARING_MASK);
mtype |= sharing; /* restore sharing bit flag */
/* here, mtype corresponds to the uncontended value for the mutex,
* i.e. something like:
*
* <tid=0><type=?><sharing=?><counter=0><state=0>
*/
for (;;) {
int oldv;
_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;
}
_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;
if (sharing) {
__futex_wait(&mutex->value, oldv, 0);
} else {
__futex_wait_private(&mutex->value, oldv, 0);
}
}
return 0;
}
int pthread_mutex_unlock(pthread_mutex_t *mutex)
{
if (__likely(mutex != NULL))
{
int mtype = (mutex->value & MUTEX_TYPE_MASK);
int mtype, tid, sharing, oldv;
if (__likely(mtype == MUTEX_TYPE_NORMAL)) {
_normal_unlock(mutex);
}
else
{
int tid = __get_thread()->kernel_id;
if (__unlikely(mutex == NULL))
return EINVAL;
if ( tid == MUTEX_OWNER(mutex) )
{
int oldv;
mtype = (mutex->value & MUTEX_TYPE_MASK);
_recursive_lock();
oldv = mutex->value;
if (oldv & MUTEX_COUNTER_MASK) {
mutex->value = oldv - (1 << MUTEX_COUNTER_SHIFT);
oldv = 0;
} else {
mutex->value = mtype;
}
_recursive_unlock();
if ((oldv & 3) == 2)
__futex_wake( &mutex->value, 1 );
}
else {
/* trying to unlock a lock we do not own */
return EPERM;
}
}
if (__likely(mtype == MUTEX_TYPE_NORMAL)) {
_normal_unlock(mutex);
return 0;
}
return EINVAL;
tid = __get_thread()->kernel_id;
sharing = (mutex->value & MUTEX_SHARING_MASK);
mtype |= sharing; /* restore sharing bit flag */
/* ensure that we own the mutex */
if (__unlikely(tid != MUTEX_OWNER(mutex)))
return EPERM;
/* decrement or unlock it */
_recursive_lock();
oldv = mutex->value;
if (oldv & MUTEX_COUNTER_MASK) {
/* decrement non-0 counter */
mutex->value = oldv - (1 << MUTEX_COUNTER_SHIFT);
oldv = 0;
} else {
/* counter was 0, revert to uncontended value */
mutex->value = mtype;
}
_recursive_unlock();
/* if the mutex was contended, wake one waiting thread */
if ((oldv & 3) == 2) {
if (sharing) {
__futex_wake(&mutex->value, 1);
} else {
__futex_wake_private(&mutex->value, 1);
}
}
return 0;
}
int pthread_mutex_trylock(pthread_mutex_t *mutex)
{
if (__likely(mutex != NULL))
int mtype, sharing, tid, oldv;
if (__unlikely(mutex == NULL))
return EINVAL;
mtype = (mutex->value & MUTEX_TYPE_MASK);
/* handle normal mutex first */
if ( __likely(mtype == MUTEX_TYPE_NORMAL) )
{
int mtype = (mutex->value & MUTEX_TYPE_MASK);
if ( __likely(mtype == MUTEX_TYPE_NORMAL) )
{
if (__atomic_cmpxchg(0, 1, &mutex->value) == 0)
return 0;
return EBUSY;
}
else
{
int tid = __get_thread()->kernel_id;
int oldv;
if ( tid == MUTEX_OWNER(mutex) )
{
int oldv, counter;
if (mtype == MUTEX_TYPE_ERRORCHECK) {
/* already locked by ourselves */
return EDEADLK;
}
_recursive_lock();
oldv = mutex->value;
counter = (oldv + (1 << MUTEX_COUNTER_SHIFT)) & MUTEX_COUNTER_MASK;
mutex->value = (oldv & ~MUTEX_COUNTER_MASK) | counter;
_recursive_unlock();
return 0;
}
/* try to lock it */
_recursive_lock();
oldv = mutex->value;
if (oldv == mtype) /* uncontended released lock => state 1 */
mutex->value = ((tid << 16) | mtype | 1);
_recursive_unlock();
if (oldv != mtype)
return EBUSY;
int sharing = (mutex->value & MUTEX_SHARING_MASK);
if (__atomic_cmpxchg(sharing|0, sharing|1, &mutex->value) == 0)
return 0;
}
return EBUSY;
}
return EINVAL;
/* recursive or errorcheck mutex, do we already own it ? */
tid = __get_thread()->kernel_id;
sharing = mutex->value & MUTEX_SHARING_MASK;
if ( tid == MUTEX_OWNER(mutex) )
{
int counter;
if (mtype == MUTEX_TYPE_ERRORCHECK) {
/* already locked by ourselves */
return EDEADLK;
}
_recursive_lock();
oldv = mutex->value;
counter = (oldv + (1 << MUTEX_COUNTER_SHIFT)) & MUTEX_COUNTER_MASK;
mutex->value = (oldv & ~MUTEX_COUNTER_MASK) | counter;
_recursive_unlock();
return 0;
}
/* we don't own it, so try to get it */
mtype |= sharing;
/* try to lock it */
_recursive_lock();
oldv = mutex->value;
if (oldv == mtype) /* uncontended released lock => state 1 */
mutex->value = ((tid << 16) | mtype | 1);
_recursive_unlock();
if (oldv != mtype)
return EBUSY;
return 0;
}
@@ -1164,16 +1247,21 @@ int pthread_mutex_lock_timeout_np(pthread_mutex_t *mutex, unsigned msecs)
clockid_t clock = CLOCK_MONOTONIC;
struct timespec abstime;
struct timespec ts;
int mtype, tid, oldv, sharing, new_lock_type;
/* compute absolute expiration time */
__timespec_to_relative_msec(&abstime, msecs, clock);
if (__likely(mutex != NULL))
{
int mtype = (mutex->value & MUTEX_TYPE_MASK);
if (__unlikely(mutex == NULL))
return EINVAL;
if ( __likely(mtype == MUTEX_TYPE_NORMAL) )
{
/* handle normal mutexes first */
mtype = (mutex->value & MUTEX_TYPE_MASK);
if ( __likely(mtype == MUTEX_TYPE_NORMAL) )
{
if (__likely(!MUTEX_IS_SHARED(mutex))) {
/* fast path for unconteded lock */
if (__atomic_cmpxchg(0, 1, &mutex->value) == 0)
return 0;
@@ -1183,77 +1271,125 @@ int pthread_mutex_lock_timeout_np(pthread_mutex_t *mutex, unsigned msecs)
if (__timespec_to_absolute(&ts, &abstime, clock) < 0)
return EBUSY;
__futex_wait(&mutex->value, 2, &ts);
__futex_wait_private(&mutex->value, 2, &ts);
}
} else /* sharing */ {
const int sharing = MUTEX_SHARING_MASK;
if (__atomic_cmpxchg(sharing|0, sharing|1, &mutex->value) == 0)
return 0;
/* loop while needed */
while (__atomic_swap(sharing|2, &mutex->value) != (sharing|0)) {
if (__timespec_to_absolute(&ts, &abstime, clock) < 0)
return EBUSY;
__futex_wait(&mutex->value, sharing|2, &ts);
}
return 0;
}
else
{
int tid = __get_thread()->kernel_id;
int oldv;
return 0;
}
if ( tid == MUTEX_OWNER(mutex) )
{
int oldv, counter;
/* recursive or errorcheck - do we own the mutex ? */
tid = __get_thread()->kernel_id;
if (mtype == MUTEX_TYPE_ERRORCHECK) {
/* already locked by ourselves */
return EDEADLK;
}
if ( tid == MUTEX_OWNER(mutex) )
{
int counter;
_recursive_lock();
oldv = mutex->value;
counter = (oldv + (1 << MUTEX_COUNTER_SHIFT)) & MUTEX_COUNTER_MASK;
mutex->value = (oldv & ~MUTEX_COUNTER_MASK) | counter;
_recursive_unlock();
return 0;
}
else
{
/*
* If the new lock is available immediately, we grab it in
* the "uncontended" state.
*/
int new_lock_type = 1;
if (mtype == MUTEX_TYPE_ERRORCHECK) {
/* already locked by ourselves */
return EDEADLK;
}
for (;;) {
int oldv;
struct timespec ts;
_recursive_lock();
oldv = mutex->value;
counter = (oldv + (1 << MUTEX_COUNTER_SHIFT)) & MUTEX_COUNTER_MASK;
mutex->value = (oldv & ~MUTEX_COUNTER_MASK) | counter;
_recursive_unlock();
return 0;
}
_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;
}
_recursive_unlock();
/* we don't own it, try to lock it */
new_lock_type = 1;
sharing = (mutex->value & MUTEX_SHARING_MASK);
if (oldv == mtype)
break;
mtype |= sharing;
/*
* 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;
for (;;) {
struct timespec ts;
if (__timespec_to_absolute(&ts, &abstime, clock) < 0)
return EBUSY;
_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;
}
_recursive_unlock();
__futex_wait( &mutex->value, oldv, &ts );
}
return 0;
}
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;
if (__timespec_to_absolute(&ts, &abstime, clock) < 0)
return EBUSY;
if (sharing) {
__futex_wait(&mutex->value, oldv, &ts);
} else {
__futex_wait_private(&mutex->value, oldv, &ts);
}
}
return EINVAL;
return 0;
}
int
pthread_condattr_init(pthread_condattr_t *attr)
{
*attr = PTHREAD_PROCESS_PRIVATE;
return 0;
}
int
pthread_condattr_setpshared(pthread_condattr_t *attr, int pshared)
{
if (attr == NULL)
return EINVAL;
if (pshared != PTHREAD_PROCESS_PRIVATE &&
pshared != PTHREAD_PROCESS_SHARED)
return EINVAL;
*attr = pshared;
return 0;
}
int
pthread_condattr_getpshared(pthread_condattr_t *attr, int *pshared)
{
if (attr == NULL || pshared == NULL)
return EINVAL;
*pshared = *attr;
return 0;
}
int
pthread_condattr_destroy(pthread_condattr_t *attr)
{
*attr = 0xdeada11d;
return 0;
}
/* XXX *technically* there is a race condition that could allow
* XXX a signal to be missed. If thread A is preempted in _wait()
* XXX after unlocking the mutex and before waiting, and if other
@@ -1262,10 +1398,29 @@ int pthread_mutex_lock_timeout_np(pthread_mutex_t *mutex, unsigned msecs)
* XXX then the signal will be lost.
*/
/* Condition variables:
* bits name description
* 0 sharing 1 if process-shared, 0 if private
* 2-31 counter counter increment on each signal/broadcast
*/
#define COND_SHARING_MASK 0x0001
#define COND_COUNTER_INCREMENT 0x0002
#define COND_COUNTER_MASK (~COND_SHARING_MASK)
#define COND_IS_SHARED(cond) (((cond)->value & COND_SHARING_MASK) != 0)
int pthread_cond_init(pthread_cond_t *cond,
const pthread_condattr_t *attr)
{
if (cond == NULL)
return EINVAL;
cond->value = 0;
if (attr != NULL && *attr == PTHREAD_PROCESS_SHARED)
cond->value |= COND_SHARING_MASK;
return 0;
}
@@ -1275,17 +1430,53 @@ int pthread_cond_destroy(pthread_cond_t *cond)
return 0;
}
/* This function is used by pthread_cond_broadcast and
* pthread_cond_signal to 'pulse' the condition variable.
*
* This means atomically decrementing the counter value
* while leaving the other bits untouched.
*/
static void
__pthread_cond_pulse(pthread_cond_t *cond)
{
long flags = (cond->value & ~COND_COUNTER_MASK);
for (;;) {
long oldval = cond->value;
long newval = ((oldval - COND_COUNTER_INCREMENT) & COND_COUNTER_MASK) | flags;
if (__atomic_cmpxchg(oldval, newval, &cond->value) == 0)
break;
}
}
int pthread_cond_broadcast(pthread_cond_t *cond)
{
__atomic_dec(&cond->value);
__futex_wake(&cond->value, INT_MAX);
if (cond == NULL)
return EINVAL;
__pthread_cond_pulse(cond);
if (COND_IS_SHARED(cond)) {
__futex_wake(&cond->value, INT_MAX);
} else {
__futex_wake_private(&cond->value, INT_MAX);
}
return 0;
}
int pthread_cond_signal(pthread_cond_t *cond)
{
__atomic_dec(&cond->value);
__futex_wake(&cond->value, 1);
if (cond == NULL)
return EINVAL;
__pthread_cond_pulse(cond);
if (COND_IS_SHARED(cond)) {
__futex_wake(&cond->value, 1);
} else {
__futex_wake_private(&cond->value, 1);
}
return 0;
}
@@ -1302,7 +1493,11 @@ int __pthread_cond_timedwait_relative(pthread_cond_t *cond,
int oldvalue = cond->value;
pthread_mutex_unlock(mutex);
status = __futex_wait(&cond->value, oldvalue, reltime);
if (COND_IS_SHARED(cond)) {
status = __futex_wait(&cond->value, oldvalue, reltime);
} else {
status = __futex_wait_private(&cond->value, oldvalue, reltime);
}
pthread_mutex_lock(mutex);
if (status == (-ETIMEDOUT)) return ETIMEDOUT;

10
libc/docs/CHANGES.TXT
View File

@@ -80,6 +80,16 @@ Differences between current and Android 2.1:
an unknown domain name. Due to an initialization bug, a random DNS search
list was generated for each thread is net.dns.search is not defined.
- <pthread.h>: Add pthread_condattr_init/destroy/setpshared/getpshared.
Also modify mutex and condvar implementation to use private futexes by
default, unless PROCESS_SHARED is specified in the init attributes.
Private futexes are limited to a single address space and can't be shared
among processes. However they are much faster to wake/wait for. This should
speed up mutex and condvar operations.
NOTE: PROCESS_SHARED mutexes are still NOT robust (see note below).
-------------------------------------------------------------------------------
Differences between Android 2.1 and 2.0.1:

5
libc/include/pthread.h
View File

@@ -165,6 +165,11 @@ int pthread_mutex_unlock(pthread_mutex_t *mutex);
int pthread_mutex_trylock(pthread_mutex_t *mutex);
int pthread_mutex_timedlock(pthread_mutex_t *mutex, struct timespec* ts);
int pthread_condattr_init(pthread_condattr_t *attr);
int pthread_condattr_setpshared(pthread_condattr_t *attr, int pshared);
int pthread_condattr_getpshared(pthread_condattr_t *attr, int *pshared);
int pthread_condattr_destroy(pthread_condattr_t *attr);
int pthread_cond_init(pthread_cond_t *cond,
const pthread_condattr_t *attr);
int pthread_cond_destroy(pthread_cond_t *cond);