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.

linuxthreads/spinlock.c

@@ -12,15 +12,130 @@
 /* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the        */
 /* GNU Library General Public License for more details.                 */
 
-/* Spin locks */
+/* Internal locks */
 
 #include <sched.h>
 #include <time.h>
 #include "pthread.h"
 #include "internals.h"
 #include "spinlock.h"
+#include "restart.h"
 
-/* This function is called if the inlined test-and-set in acquire() failed */
+/* The status field of a fastlock has the following meaning:
+     0: fastlock is free
+     1: fastlock is taken, no thread is waiting on it
+  ADDR: fastlock is taken, ADDR is address of thread descriptor for
+        first waiting thread, other waiting threads are linked via
+        their p_nextwaiting field.
+   The waiting list is not sorted by priority order.
+   Actually, we always insert at top of list (sole insertion mode
+   that can be performed without locking).
+   For __pthread_unlock, we perform a linear search in the list
+   to find the highest-priority, oldest waiting thread.
+   This is safe because there are no concurrent __pthread_unlock
+   operations -- only the thread that locked the mutex can unlock it. */
+
+void __pthread_lock(struct _pthread_fastlock * lock)
+{
+  long oldstatus, newstatus;
+  pthread_descr self = NULL;
+
+  do {
+    oldstatus = lock->status;
+    if (oldstatus == 0) {
+      newstatus = 1;
+    } else {
+      self = thread_self();
+      self->p_nextwaiting = (pthread_descr) oldstatus;
+      newstatus = (long) self;
+    }
+  } while(! compare_and_swap(&lock->status, oldstatus, newstatus,
+                             &lock->spinlock));
+  if (oldstatus != 0) suspend(self);
+}
+
+int __pthread_trylock(struct _pthread_fastlock * lock)
+{
+  long oldstatus;
+
+  do {
+    oldstatus = lock->status;
+    if (oldstatus != 0) return EBUSY;
+  } while(! compare_and_swap(&lock->status, 0, 1, &lock->spinlock));
+  return 0;
+}
+
+void __pthread_unlock(struct _pthread_fastlock * lock)
+{
+  long oldstatus;
+  pthread_descr thr, * ptr, * maxptr;
+  int maxprio;
+
+again:
+  oldstatus = lock->status;
+  if (oldstatus == 1) {
+    /* No threads are waiting for this lock */
+    if (! compare_and_swap(&lock->status, 1, 0, &lock->spinlock)) goto again;
+    return;
+  }
+  /* Find thread in waiting queue with maximal priority */
+  ptr = (pthread_descr *) &lock->status;
+  thr = (pthread_descr) oldstatus;
+  maxprio = 0;
+  maxptr = ptr;
+  while (thr != (pthread_descr) 1) {
+    if (thr->p_priority >= maxprio) {
+      maxptr = ptr;
+      maxprio = thr->p_priority;
+    }
+    ptr = &(thr->p_nextwaiting);
+    thr = *ptr;
+  }
+  /* Remove max prio thread from waiting list. */
+  if (maxptr == (pthread_descr *) &lock->status) {
+    /* If max prio thread is at head, remove it with compare-and-swap
+       to guard against concurrent lock operation */
+    thr = (pthread_descr) oldstatus;
+    if (! compare_and_swap(&lock->status,
+                           oldstatus, (long)(thr->p_nextwaiting),
+                           &lock->spinlock))
+      goto again;
+  } else {
+    /* No risk of concurrent access, remove max prio thread normally */
+    thr = *maxptr;
+    *maxptr = thr->p_nextwaiting;
+  }
+  /* Wake up the selected waiting thread */
+  thr->p_nextwaiting = NULL;
+  restart(thr);
+}
+
+/* Compare-and-swap emulation with a spinlock */
+
+#ifdef TEST_FOR_COMPARE_AND_SWAP
+int __pthread_has_cas = 0;
+#endif
+
+#ifndef HAS_COMPARE_AND_SWAP
+
+static void __pthread_acquire(int * spinlock);
+
+int __pthread_compare_and_swap(long * ptr, long oldval, long newval,
+                               int * spinlock)
+{
+  int res;
+  if (testandset(spinlock)) __pthread_acquire(spinlock);
+  if (*ptr == oldval) {
+    *ptr = newval; res = 1;
+  } else {
+    res = 0;
+  }
+  *spinlock = 0;
+  return res;
+}
+
+/* This function is called if the inlined test-and-set
+   in __pthread_compare_and_swap() failed */
 
 /* The retry strategy is as follows:
    - We test and set the spinlock MAX_SPIN_COUNT times, calling
@@ -40,7 +155,7 @@
    - When nanosleep() returns, we try again, doing MAX_SPIN_COUNT
      sched_yield(), then sleeping again if needed. */
 
-void __pthread_acquire(int * spinlock)
+static void __pthread_acquire(int * spinlock)
 {
   int cnt = 0;
   struct timespec tm;
@@ -57,3 +172,5 @@ void __pthread_acquire(int * spinlock)
     }
   }
 }
+
+#endif