Author: davidxu
Date: Wed Mar 21 07:12:52 2012
New Revision: 233262
URL: http://svn.freebsd.org/changeset/base/233262
Log:
Use version 2 of semaphore provided by kernel umtx code, now if there is
no waiters, we still increase and decrease count in user mode without
entering kernel, once there is a waiter, sem_post will enter kernel to
increase count and wake thread up, this is atomicy and allow us to
gracefully destroy semaphore after sem_wait returned.
Modified:
head/lib/libc/gen/sem_new.c
Modified: head/lib/libc/gen/sem_new.c
==============================================================================
--- head/lib/libc/gen/sem_new.c Wed Mar 21 07:07:43 2012 (r233261)
+++ head/lib/libc/gen/sem_new.c Wed Mar 21 07:12:52 2012 (r233262)
@@ -61,7 +61,8 @@ __weak_reference(_sem_unlink, sem_unlink
__weak_reference(_sem_wait, sem_wait);
#define SEM_PREFIX "/tmp/SEMD"
-#define SEM_MAGIC ((u_int32_t)0x73656d31)
+#define SEM_MAGIC1 ((u_int32_t)0x73656d31)
+#define SEM_MAGIC ((u_int32_t)0x73656d32)
struct sem_nameinfo {
int open_count;
@@ -109,7 +110,7 @@ static inline int
sem_check_validity(sem_t *sem)
{
- if (sem->_magic == SEM_MAGIC)
+ if (sem->_magic == SEM_MAGIC || sem->_magic == SEM_MAGIC1)
return (0);
else {
errno = EINVAL;
@@ -130,7 +131,7 @@ _sem_init(sem_t *sem, int pshared, unsig
sem->_magic = SEM_MAGIC;
sem->_kern._count = (u_int32_t)value;
sem->_kern._has_waiters = 0;
- sem->_kern._flags = pshared ? USYNC_PROCESS_SHARED : 0;
+ sem->_kern._flags = (pshared ? USYNC_PROCESS_SHARED : 0) | SEM_VER2;
return (0);
}
@@ -207,7 +208,7 @@ _sem_open(const char *name, int flags, .
tmp._magic = SEM_MAGIC;
tmp._kern._has_waiters = 0;
tmp._kern._count = value;
- tmp._kern._flags = USYNC_PROCESS_SHARED | SEM_NAMED;
+ tmp._kern._flags = USYNC_PROCESS_SHARED | SEM_NAMED | SEM_VER2;
if (_write(fd, &tmp, sizeof(tmp)) != sizeof(tmp)) {
flock(fd, LOCK_UN);
goto error;
@@ -325,20 +326,11 @@ _sem_getvalue(sem_t * __restrict sem, in
if (sem_check_validity(sem) != 0)
return (-1);
- *sval = (int)sem->_kern._count;
+ *sval = (int)sem->_kern._count & ~SEM_WAITERS;
return (0);
}
static __inline int
-usem_wake(struct _usem *sem)
-{
- rmb();
- if (!sem->_has_waiters)
- return (0);
- return _umtx_op(sem, UMTX_OP_SEM_WAKE, 0, NULL, NULL);
-}
-
-static __inline int
usem_wait(struct _usem *sem, const struct timespec *abstime)
{
struct _umtx_time *tm_p, timeout;
@@ -358,48 +350,51 @@ usem_wait(struct _usem *sem, const struc
(void *)tm_size, __DECONST(void*, tm_p));
}
+static inline int
+_trywait(sem_t *sem)
+{
+ int count;
+
+ if ((sem->_kern._flags & SEM_VER2) != 0) {
+ while (((count = sem->_kern._count) & ~SEM_WAITERS) > 0) {
+ if (atomic_cmpset_acq_int(&sem->_kern._count, count,
count - 1))
+ return (0);
+ }
+ } else {
+ while ((count = sem->_kern._count) > 0) {
+ if (atomic_cmpset_acq_int(&sem->_kern._count, count,
count - 1))
+ return (0);
+ }
+ }
+ return (EAGAIN);
+}
+
int
_sem_trywait(sem_t *sem)
{
- int val;
+ int status;
if (sem_check_validity(sem) != 0)
return (-1);
-
- while ((val = sem->_kern._count) > 0) {
- if (atomic_cmpset_acq_int(&sem->_kern._count, val, val - 1))
- return (0);
- }
- errno = EAGAIN;
+ if ((status = _trywait(sem)) == 0)
+ return (0);
+ errno = status;
return (-1);
}
-#define TIMESPEC_SUB(dst, src, val) \
- do { \
- (dst)->tv_sec = (src)->tv_sec - (val)->tv_sec; \
- (dst)->tv_nsec = (src)->tv_nsec - (val)->tv_nsec; \
- if ((dst)->tv_nsec < 0) { \
- (dst)->tv_sec--; \
- (dst)->tv_nsec += 1000000000; \
- } \
- } while (0)
-
-
int
_sem_timedwait(sem_t * __restrict sem,
const struct timespec * __restrict abstime)
{
- int val, retval;
+ int retval;
if (sem_check_validity(sem) != 0)
return (-1);
retval = 0;
for (;;) {
- while ((val = sem->_kern._count) > 0) {
- if (atomic_cmpset_acq_int(&sem->_kern._count, val, val
- 1))
- return (0);
- }
+ if (_trywait(sem) == 0)
+ return (0);
if (retval) {
_pthread_testcancel();
@@ -438,10 +433,36 @@ _sem_wait(sem_t *sem)
int
_sem_post(sem_t *sem)
{
+ int count;
if (sem_check_validity(sem) != 0)
return (-1);
- atomic_add_rel_int(&sem->_kern._count, 1);
- return usem_wake(&sem->_kern);
+ if ((sem->_kern._flags & SEM_VER2) != 0) {
+ for (;;) {
+ count = sem->_kern._count;
+ if ((count & SEM_WAITERS) == 0) {
+ if (__predict_false(count == SEM_VALUE_MAX)) {
+ errno = ERANGE;
+ return (-1);
+ }
+ if (atomic_cmpset_rel_int(&sem->_kern._count,
count, count+1))
+ return (0);
+ } else {
+ return _umtx_op(&sem->_kern, UMTX_OP_SEM_WAKE,
0, NULL, NULL);
+ }
+ }
+ } else {
+ do {
+ count = sem->_kern._count;
+ if (__predict_false(count == SEM_VALUE_MAX)) {
+ errno = ERANGE;
+ return (-1);
+ }
+ } while (!atomic_cmpset_rel_int(&sem->_kern._count, count,
count+1));
+ rmb();
+ if (!sem->_kern._has_waiters)
+ return (0);
+ return _umtx_op(&sem->_kern, UMTX_OP_SEM_WAKE, 0, NULL, NULL);
+ }
}
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