Use private futexes for semaphores, unless they are initialized with pshared != 0.
Change-Id: I534e36a7171cd37037ae03b910ba71ea6968286d
Note: previously, sem_init() would return an error if pshared != 0.
diff --git a/libc/bionic/pthread.c b/libc/bionic/pthread.c
index 6fd47f2..ac5e6bf 100644
--- a/libc/bionic/pthread.c
+++ b/libc/bionic/pthread.c
@@ -43,7 +43,7 @@
#include <memory.h>
#include <assert.h>
#include <malloc.h>
-#include <linux/futex.h>
+#include <bionic_futex.h>
#include <cutils/atomic-inline.h>
#include <sys/prctl.h>
#include <sys/stat.h>
@@ -54,6 +54,16 @@
extern void _exit_thread(int retCode);
extern int __set_errno(int);
+int __futex_wake_ex(volatile void *ftx, int pshared, int val)
+{
+ return __futex_syscall3(ftx, pshared ? FUTEX_WAKE : FUTEX_WAKE_PRIVATE, val);
+}
+
+int __futex_wait_ex(volatile void *ftx, int pshared, int val, const struct timespec *timeout)
+{
+ return __futex_syscall4(ftx, pshared ? FUTEX_WAIT : FUTEX_WAIT_PRIVATE, val, timeout);
+}
+
#define __likely(cond) __builtin_expect(!!(cond), 1)
#define __unlikely(cond) __builtin_expect(!!(cond), 0)
@@ -716,24 +726,6 @@
}
-int __futex_wait(volatile void *ftx, int val, const struct timespec *timeout);
-int __futex_wake(volatile void *ftx, int count);
-
-int __futex_syscall3(volatile void *ftx, int op, int val);
-int __futex_syscall4(volatile void *ftx, int op, int val, const struct timespec *timeout);
-
-#ifndef FUTEX_PRIVATE_FLAG
-#define FUTEX_PRIVATE_FLAG 128
-#endif
-
-#ifndef FUTEX_WAIT_PRIVATE
-#define FUTEX_WAIT_PRIVATE (FUTEX_WAIT|FUTEX_PRIVATE_FLAG)
-#endif
-
-#ifndef FUTEX_WAKE_PRIVATE
-#define FUTEX_WAKE_PRIVATE (FUTEX_WAKE|FUTEX_PRIVATE_FLAG)
-#endif
-
// mutex lock states
//
// 0: unlocked
@@ -935,10 +927,8 @@
* that the mutex is in state 2 when we go to sleep on it, which
* guarantees a wake-up call.
*/
- int wait_op = shared ? FUTEX_WAIT : FUTEX_WAIT_PRIVATE;
-
while (__atomic_swap(shared|2, &mutex->value ) != (shared|0))
- __futex_syscall4(&mutex->value, wait_op, shared|2, 0);
+ __futex_wait_ex(&mutex->value, shared, shared|2, 0);
}
ANDROID_MEMBAR_FULL();
}
@@ -961,7 +951,6 @@
* if it wasn't 1 we have to do some additional work.
*/
if (__atomic_dec(&mutex->value) != (shared|1)) {
- int wake_op = shared ? FUTEX_WAKE : FUTEX_WAKE_PRIVATE;
/*
* Start by releasing the lock. The decrement changed it from
* "contended lock" to "uncontended lock", which means we still
@@ -999,7 +988,7 @@
* Either way we have correct behavior and nobody is orphaned on
* the wait queue.
*/
- __futex_syscall3(&mutex->value, wake_op, 1);
+ __futex_wake_ex(&mutex->value, shared, 1);
}
}
@@ -1019,7 +1008,7 @@
int pthread_mutex_lock(pthread_mutex_t *mutex)
{
- int mtype, tid, new_lock_type, shared, wait_op;
+ int mtype, tid, new_lock_type, shared;
if (__unlikely(mutex == NULL))
return EINVAL;
@@ -1064,8 +1053,7 @@
new_lock_type = 1;
/* compute futex wait opcode and restore shared flag in mtype */
- wait_op = shared ? FUTEX_WAIT : FUTEX_WAIT_PRIVATE;
- mtype |= shared;
+ mtype |= shared;
for (;;) {
int oldv;
@@ -1091,7 +1079,7 @@
*/
new_lock_type = 2;
- __futex_syscall4(&mutex->value, wait_op, oldv, NULL);
+ __futex_wait_ex(&mutex->value, shared, oldv, NULL);
}
return 0;
}
@@ -1131,8 +1119,7 @@
/* Wake one waiting thread, if any */
if ((oldv & 3) == 2) {
- int wake_op = shared ? FUTEX_WAKE : FUTEX_WAKE_PRIVATE;
- __futex_syscall3(&mutex->value, wake_op, 1);
+ __futex_wake_ex(&mutex->value, shared, 1);
}
return 0;
}
@@ -1234,7 +1221,7 @@
clockid_t clock = CLOCK_MONOTONIC;
struct timespec abstime;
struct timespec ts;
- int mtype, tid, oldv, new_lock_type, shared, wait_op;
+ int mtype, tid, oldv, new_lock_type, shared;
/* compute absolute expiration time */
__timespec_to_relative_msec(&abstime, msecs, clock);
@@ -1248,8 +1235,6 @@
/* Handle common case first */
if ( __likely(mtype == MUTEX_TYPE_NORMAL) )
{
- int wait_op = shared ? FUTEX_WAIT : FUTEX_WAIT_PRIVATE;
-
/* fast path for uncontended lock */
if (__atomic_cmpxchg(shared|0, shared|1, &mutex->value) == 0) {
ANDROID_MEMBAR_FULL();
@@ -1261,7 +1246,7 @@
if (__timespec_to_absolute(&ts, &abstime, clock) < 0)
return EBUSY;
- __futex_syscall4(&mutex->value, wait_op, shared|2, &ts);
+ __futex_wait_ex(&mutex->value, shared, shared|2, &ts);
}
ANDROID_MEMBAR_FULL();
return 0;
@@ -1294,7 +1279,6 @@
new_lock_type = 1;
/* Compute wait op and restore sharing bit in mtype */
- wait_op = shared ? FUTEX_WAIT : FUTEX_WAIT_PRIVATE;
mtype |= shared;
for (;;) {
@@ -1325,7 +1309,7 @@
if (__timespec_to_absolute(&ts, &abstime, clock) < 0)
return EBUSY;
- __futex_syscall4(&mutex->value, wait_op, oldv, &ts);
+ __futex_wait_ex(&mutex->value, shared, oldv, &ts);
}
return 0;
}
@@ -1418,7 +1402,6 @@
__pthread_cond_pulse(pthread_cond_t *cond, int counter)
{
long flags;
- int wake_op;
if (__unlikely(cond == NULL))
return EINVAL;
@@ -1432,8 +1415,7 @@
break;
}
- wake_op = COND_IS_SHARED(cond) ? FUTEX_WAKE : FUTEX_WAKE_PRIVATE;
- __futex_syscall3(&cond->value, wake_op, counter);
+ __futex_wake_ex(&cond->value, COND_IS_SHARED(cond), counter);
return 0;
}
@@ -1458,10 +1440,9 @@
{
int status;
int oldvalue = cond->value;
- int wait_op = COND_IS_SHARED(cond) ? FUTEX_WAIT : FUTEX_WAIT_PRIVATE;
pthread_mutex_unlock(mutex);
- status = __futex_syscall4(&cond->value, wait_op, oldvalue, reltime);
+ status = __futex_wait_ex(&cond->value, COND_IS_SHARED(cond), oldvalue, reltime);
pthread_mutex_lock(mutex);
if (status == (-ETIMEDOUT)) return ETIMEDOUT;
diff --git a/libc/bionic/semaphore.c b/libc/bionic/semaphore.c
index b624943..39d049a 100644
--- a/libc/bionic/semaphore.c
+++ b/libc/bionic/semaphore.c
@@ -31,6 +31,16 @@
#include <sys/atomics.h>
#include <time.h>
#include <cutils/atomic-inline.h>
+#include <bionic_futex.h>
+
+/* Use the lower 31-bits for the counter, and the high bit for
+ * the shared flag.
+ */
+#define SEM_VALUE_MASK 0x7fffffff
+#define SEM_SHARED_MASK 0x80000000
+
+#define SEM_GET_SHARED(sem) ((sem)->count & SEM_SHARED_MASK)
+#define SEM_GET_VALUE(sem) ((sem)->count & SEM_VALUE_MASK)
int sem_init(sem_t *sem, int pshared, unsigned int value)
{
@@ -39,12 +49,16 @@
return -1;
}
- if (pshared != 0) {
- errno = ENOSYS;
+ /* ensure that 'value' can be stored in the semaphore */
+ if ((value & SEM_VALUE_MASK) != value) {
+ errno = EINVAL;
return -1;
}
sem->count = value;
+ if (pshared != 0)
+ sem->count |= SEM_SHARED_MASK;
+
return 0;
}
@@ -55,10 +69,11 @@
errno = EINVAL;
return -1;
}
- if (sem->count == 0) {
+ if ((sem->count & SEM_VALUE_MASK) == 0) {
errno = EBUSY;
return -1;
}
+ sem->count = 0;
return 0;
}
@@ -91,32 +106,60 @@
}
+/* Return 0 if a semaphore's value is 0
+ * Otherwise, decrement the value and return the old value.
+ */
static int
-__atomic_dec_if_positive( volatile unsigned int* pvalue )
+__sem_dec_if_positive(volatile unsigned int *pvalue)
{
+ unsigned int shared = (*pvalue & SEM_SHARED_MASK);
unsigned int old;
do {
- old = *pvalue;
+ old = (*pvalue & SEM_VALUE_MASK);
}
- while ( old != 0 && __atomic_cmpxchg( (int)old, (int)old-1, (volatile int*)pvalue ) != 0 );
+ while ( old != 0 &&
+ __atomic_cmpxchg((int)(old|shared),
+ (int)((old-1)|shared),
+ (volatile int*)pvalue) != 0 );
return old;
}
+/* Increment the value of a semaphore atomically.
+ * NOTE: the value will wrap above SEM_VALUE_MASK
+ */
+static int
+__sem_inc(volatile unsigned int *pvalue)
+{
+ unsigned int shared = (*pvalue & SEM_SHARED_MASK);
+ unsigned int old;
+
+ do {
+ old = (*pvalue & SEM_VALUE_MASK);
+ } while ( __atomic_cmpxchg((int)(old|shared),
+ (int)(((old+1)&SEM_VALUE_MASK)|shared),
+ (volatile int*)pvalue) != 0);
+ return old;
+}
+
/* lock a semaphore */
int sem_wait(sem_t *sem)
{
+ unsigned shared;
+
if (sem == NULL) {
errno = EINVAL;
return -1;
}
+ shared = SEM_GET_SHARED(sem);
+
for (;;) {
- if (__atomic_dec_if_positive(&sem->count))
+ if (__sem_dec_if_positive(&sem->count))
break;
- __futex_wait(&sem->count, 0, 0);
+ __futex_wait_ex(&sem->count, shared, shared, NULL);
}
ANDROID_MEMBAR_FULL();
return 0;
@@ -125,6 +168,7 @@
int sem_timedwait(sem_t *sem, const struct timespec *abs_timeout)
{
int ret;
+ unsigned int shared;
if (sem == NULL) {
errno = EINVAL;
@@ -133,7 +177,7 @@
/* POSIX says we need to try to decrement the semaphore
* before checking the timeout value */
- if (__atomic_dec_if_positive(&sem->count)) {
+ if (__sem_dec_if_positive(&sem->count)) {
ANDROID_MEMBAR_FULL();
return 0;
}
@@ -148,6 +192,8 @@
return -1;
}
+ shared = SEM_GET_SHARED(sem);
+
for (;;) {
struct timespec ts;
int ret;
@@ -166,7 +212,7 @@
return -1;
}
- ret = __futex_wait(&sem->count, 0, &ts);
+ ret = __futex_wait_ex(&sem->count, shared, shared, &ts);
/* return in case of timeout or interrupt */
if (ret == -ETIMEDOUT || ret == -EINTR) {
@@ -174,7 +220,7 @@
return -1;
}
- if (__atomic_dec_if_positive(&sem->count)) {
+ if (__sem_dec_if_positive(&sem->count)) {
ANDROID_MEMBAR_FULL();
break;
}
@@ -185,12 +231,16 @@
/* unlock a semaphore */
int sem_post(sem_t *sem)
{
+ unsigned int shared;
+
if (sem == NULL)
return EINVAL;
+ shared = SEM_GET_SHARED(sem);
+
ANDROID_MEMBAR_FULL();
- if (__atomic_inc((volatile int*)&sem->count) >= 0)
- __futex_wake(&sem->count, 1);
+ if (__sem_inc(&sem->count) >= 0)
+ __futex_wake_ex(&sem->count, shared, 1);
return 0;
}
@@ -202,7 +252,7 @@
return -1;
}
- if (__atomic_dec_if_positive(&sem->count) > 0) {
+ if (__sem_dec_if_positive(&sem->count) > 0) {
ANDROID_MEMBAR_FULL();
return 0;
} else {
@@ -218,6 +268,6 @@
return -1;
}
- *sval = sem->count;
+ *sval = SEM_GET_VALUE(sem);
return 0;
}