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authorUlrich Drepper <drepper@redhat.com>1998-06-25 19:36:00 +0000
committerUlrich Drepper <drepper@redhat.com>1998-06-25 19:36:00 +0000
commit3387a425e65b839b68bd2973f6bc5ab22315cc5d (patch)
tree375713a0b865b10b9eddd9c9877ad68cf0bdc851 /linuxthreads/semaphore.c
parentd47aac39992cb1dd705d8c584f4d3979d7ce4602 (diff)
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Finish user stack support. Change locking code to be safe in situations with different priorities.
1998-06-25 19:27 Ulrich Drepper <drepper@cygnus.com> * attr.c: Finish user stack support. Change locking code to be safe in situations with different priorities. * cancel.c: Likewise. * condvar.c: Likewise. * internals.h: Likewise. * join.c: Likewise. * manager.c: Likewise. * mutex.c: Likewise. * pthread.c: Likewise. * ptlongjmp.c: Likewise. * queue.h: Likewise. * rwlock.c: Likewise. * semaphore.c: Likewise. * semaphore.h: Likewise. * signals.c: Likewise. * spinlock.c: Likewise. * spinlock.h: Likewise. Patches by Xavier leroy. 1998-06-25 Ulrich Drepper <drepper@cygnus.com> * sysdeps/pthread/pthread.h: Make [sg]et_stacksize and [sg]et_stackaddr prototypes always available. * sysdeps/unix/sysv/linux/bits/posix_opt.h: Define _POSIX_THREAD_ATTR_STACKSIZE and _POSIX_THREAD_ATTR_STACKADDR.
Diffstat (limited to 'linuxthreads/semaphore.c')
-rw-r--r--linuxthreads/semaphore.c236
1 files changed, 67 insertions, 169 deletions
diff --git a/linuxthreads/semaphore.c b/linuxthreads/semaphore.c
index bd07439cde..7ca609f6b2 100644
--- a/linuxthreads/semaphore.c
+++ b/linuxthreads/semaphore.c
@@ -17,69 +17,13 @@
#include "pthread.h"
#include "semaphore.h"
#include "internals.h"
-#include "restart.h"
-
-
-#if !defined HAS_COMPARE_AND_SWAP && !defined TEST_FOR_COMPARE_AND_SWAP
-/* If we have no atomic compare and swap, fake it using an extra spinlock. */
-
-#include "spinlock.h"
-static inline int sem_compare_and_swap(sem_t *sem, long oldval, long newval)
-{
- int ret;
- acquire(&sem->sem_spinlock);
- ret = (sem->sem_status == oldval);
- if (ret) sem->sem_status = newval;
- release(&sem->sem_spinlock);
- return ret;
-}
-
-#elif defined TEST_FOR_COMPARE_AND_SWAP
-
#include "spinlock.h"
-static int has_compare_and_swap = -1; /* to be determined at run-time */
-
-static inline int sem_compare_and_swap(sem_t *sem, long oldval, long newval)
-{
- int ret;
-
- if (has_compare_and_swap == 1)
- return __compare_and_swap(&sem->sem_status, oldval, newval);
-
- acquire(&sem->sem_spinlock);
- ret = (sem->sem_status == oldval);
- if (ret) sem->sem_status = newval;
- release(&sem->sem_spinlock);
- return ret;
-}
-
-#else
-/* But if we do have an atomic compare and swap, use it! */
-
-static inline int sem_compare_and_swap(sem_t *sem, long oldval, long newval)
-{
- return __compare_and_swap(&sem->sem_status, oldval, newval);
-}
-
-#endif
-
-
-/* The state of a semaphore is represented by a long int encoding
- either the semaphore count if >= 0 and no thread is waiting on it,
- or the head of the list of threads waiting for the semaphore.
- To distinguish the two cases, we encode the semaphore count N
- as 2N+1, so that it has the lowest bit set.
-
- A sequence of sem_wait operations on a semaphore initialized to N
- result in the following successive states:
- 2N+1, 2N-1, ..., 3, 1, &first_waiting_thread, &second_waiting_thread, ...
-*/
-
-static void sem_restart_list(pthread_descr waiting);
+#include "restart.h"
+#include "queue.h"
int sem_init(sem_t *sem, int pshared, unsigned int value)
{
- if ((long)value > SEM_VALUE_MAX) {
+ if (value > SEM_VALUE_MAX) {
errno = EINVAL;
return -1;
}
@@ -87,150 +31,104 @@ int sem_init(sem_t *sem, int pshared, unsigned int value)
errno = ENOSYS;
return -1;
}
-#ifdef TEST_FOR_COMPARE_AND_SWAP
- if (has_compare_and_swap == -1) {
- has_compare_and_swap = compare_and_swap_is_available();
- }
-#endif
-#if !defined HAS_COMPARE_AND_SWAP || defined TEST_FOR_COMPARE_AND_SWAP
- sem->sem_spinlock = 0;
-#endif
- sem->sem_status = ((long)value << 1) + 1;
+ __pthread_init_lock((struct _pthread_fastlock *) &sem->sem_lock);
+ sem->sem_value = value;
+ sem->sem_waiting = NULL;
return 0;
}
int sem_wait(sem_t * sem)
{
- long oldstatus, newstatus;
- volatile pthread_descr self = thread_self();
- pthread_descr * th;
+ volatile pthread_descr self;
- while (1) {
- do {
- oldstatus = sem->sem_status;
- if ((oldstatus & 1) && (oldstatus != 1))
- newstatus = oldstatus - 2;
- else {
- newstatus = (long) self;
- self->p_nextwaiting = (pthread_descr) oldstatus;
- }
- }
- while (! sem_compare_and_swap(sem, oldstatus, newstatus));
- if (newstatus & 1)
- /* We got the semaphore. */
- return 0;
- /* Wait for sem_post or cancellation */
- suspend_with_cancellation(self);
- /* This is a cancellation point */
- if (self->p_canceled && self->p_cancelstate == PTHREAD_CANCEL_ENABLE) {
- /* Remove ourselves from the waiting list if we're still on it */
- /* First check if we're at the head of the list. */
- do {
- oldstatus = sem->sem_status;
- if (oldstatus != (long) self) break;
- newstatus = (long) self->p_nextwaiting;
- }
- while (! sem_compare_and_swap(sem, oldstatus, newstatus));
- /* Now, check if we're somewhere in the list.
- There's a race condition with sem_post here, but it does not matter:
- the net result is that at the time pthread_exit is called,
- self is no longer reachable from sem->sem_status. */
- if (oldstatus != (long) self && (oldstatus & 1) == 0) {
- for (th = &(((pthread_descr) oldstatus)->p_nextwaiting);
- *th != NULL && *th != (pthread_descr) 1;
- th = &((*th)->p_nextwaiting)) {
- if (*th == self) {
- *th = self->p_nextwaiting;
- break;
- }
- }
- }
- pthread_exit(PTHREAD_CANCELED);
- }
+ __pthread_lock((struct _pthread_fastlock *) &sem->sem_lock);
+ if (sem->sem_value > 0) {
+ sem->sem_value--;
+ __pthread_unlock((struct _pthread_fastlock *) &sem->sem_lock);
+ return 0;
+ }
+ self = thread_self();
+ enqueue(&sem->sem_waiting, self);
+ /* Wait for sem_post or cancellation */
+ __pthread_unlock((struct _pthread_fastlock *) &sem->sem_lock);
+ suspend_with_cancellation(self);
+ /* This is a cancellation point */
+ if (self->p_canceled && self->p_cancelstate == PTHREAD_CANCEL_ENABLE) {
+ /* Remove ourselves from the waiting list if we're still on it */
+ __pthread_lock((struct _pthread_fastlock *) &sem->sem_lock);
+ remove_from_queue(&sem->sem_waiting, self);
+ __pthread_unlock((struct _pthread_fastlock *) &sem->sem_lock);
+ pthread_exit(PTHREAD_CANCELED);
}
+ /* We got the semaphore */
+ return 0;
}
int sem_trywait(sem_t * sem)
{
- long oldstatus, newstatus;
-
- do {
- oldstatus = sem->sem_status;
- if ((oldstatus & 1) == 0 || (oldstatus == 1)) {
- errno = EAGAIN;
- return -1;
- }
- newstatus = oldstatus - 2;
+ int retval;
+
+ __pthread_lock((struct _pthread_fastlock *) &sem->sem_lock);
+ if (sem->sem_value == 0) {
+ errno = EAGAIN;
+ retval = -1;
+ } else {
+ sem->sem_value--;
+ retval = 0;
}
- while (! sem_compare_and_swap(sem, oldstatus, newstatus));
- return 0;
+ return retval;
}
int sem_post(sem_t * sem)
{
- long oldstatus, newstatus;
-
- do {
- oldstatus = sem->sem_status;
- if ((oldstatus & 1) == 0)
- newstatus = 3;
- else {
- if (oldstatus >= SEM_VALUE_MAX) {
+ pthread_descr self = thread_self();
+ pthread_descr th;
+ struct pthread_request request;
+
+ if (self->p_in_sighandler == NULL) {
+ __pthread_lock((struct _pthread_fastlock *) &sem->sem_lock);
+ if (sem->sem_waiting == NULL) {
+ if (sem->sem_value >= SEM_VALUE_MAX) {
/* Overflow */
errno = ERANGE;
+ __pthread_unlock((struct _pthread_fastlock *) &sem->sem_lock);
+ return -1;
+ }
+ sem->sem_value++;
+ __pthread_unlock((struct _pthread_fastlock *) &sem->sem_lock);
+ } else {
+ th = dequeue(&sem->sem_waiting);
+ __pthread_unlock((struct _pthread_fastlock *) &sem->sem_lock);
+ restart(th);
+ }
+ } else {
+ /* If we're in signal handler, delegate post operation to
+ the thread manager. */
+ if (__pthread_manager_request < 0) {
+ if (__pthread_initialize_manager() < 0) {
+ errno = EAGAIN;
return -1;
}
- newstatus = oldstatus + 2;
}
+ request.req_kind = REQ_POST;
+ request.req_args.post = sem;
+ __libc_write(__pthread_manager_request,
+ (char *) &request, sizeof(request));
}
- while (! sem_compare_and_swap(sem, oldstatus, newstatus));
- if ((oldstatus & 1) == 0)
- sem_restart_list((pthread_descr) oldstatus);
return 0;
}
int sem_getvalue(sem_t * sem, int * sval)
{
- long status = sem->sem_status;
- if (status & 1)
- *sval = (int)((unsigned long) status >> 1);
- else
- *sval = 0;
+ *sval = sem->sem_value;
return 0;
}
int sem_destroy(sem_t * sem)
{
- if ((sem->sem_status & 1) == 0) {
+ if (sem->sem_waiting != NULL) {
errno = EBUSY;
return -1;
}
return 0;
}
-
-/* Auxiliary function for restarting all threads on a waiting list,
- in priority order. */
-
-static void sem_restart_list(pthread_descr waiting)
-{
- pthread_descr th, towake, *p;
-
- /* Sort list of waiting threads by decreasing priority (insertion sort) */
- towake = NULL;
- while (waiting != (pthread_descr) 1) {
- th = waiting;
- waiting = waiting->p_nextwaiting;
- p = &towake;
- while (*p != NULL && th->p_priority < (*p)->p_priority)
- p = &((*p)->p_nextwaiting);
- th->p_nextwaiting = *p;
- *p = th;
- }
- /* Wake up threads in priority order */
- while (towake != NULL) {
- th = towake;
- towake = towake->p_nextwaiting;
- th->p_nextwaiting = NULL;
- restart(th);
- }
-}