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.

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);
-  }
-}