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authorMike Frysinger <vapier@gentoo.org>2005-11-15 03:13:04 (GMT)
committerMike Frysinger <vapier@gentoo.org>2005-11-15 03:13:04 (GMT)
commita9f5aa1cc96fc2c71f19a9c3e9dcbee0e78f83ca (patch)
tree2c5d251bdfd06d0a76cec9fc507b1873b4bbbdad /libpthread/linuxthreads.old/spinlock.c
parentfd6dde5a19092be5bb1990dadd5c595d2ed0b3aa (diff)
rename current stable linuxthreads to linuxthreads.old to prepare for import of latest glibc version
Diffstat (limited to 'libpthread/linuxthreads.old/spinlock.c')
-rw-r--r--libpthread/linuxthreads.old/spinlock.c723
1 files changed, 723 insertions, 0 deletions
diff --git a/libpthread/linuxthreads.old/spinlock.c b/libpthread/linuxthreads.old/spinlock.c
new file mode 100644
index 0000000..cdf45f1
--- /dev/null
+++ b/libpthread/linuxthreads.old/spinlock.c
@@ -0,0 +1,723 @@
+/* Linuxthreads - a simple clone()-based implementation of Posix */
+/* threads for Linux. */
+/* Copyright (C) 1998 Xavier Leroy (Xavier.Leroy@inria.fr) */
+/* */
+/* This program is free software; you can redistribute it and/or */
+/* modify it under the terms of the GNU Library General Public License */
+/* as published by the Free Software Foundation; either version 2 */
+/* of the License, or (at your option) any later version. */
+/* */
+/* This program is distributed in the hope that it will be useful, */
+/* but WITHOUT ANY WARRANTY; without even the implied warranty of */
+/* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the */
+/* GNU Library General Public License for more details. */
+
+/* Internal locks */
+
+#define __FORCE_GLIBC
+#include <features.h>
+#include <errno.h>
+#include <sched.h>
+#include <time.h>
+#include <stdlib.h>
+#include <limits.h>
+#include "pthread.h"
+#include "internals.h"
+#include "spinlock.h"
+#include "restart.h"
+
+static void __pthread_acquire(int * spinlock);
+
+static inline void __pthread_release(int * spinlock)
+{
+ WRITE_MEMORY_BARRIER();
+ *spinlock = __LT_SPINLOCK_INIT;
+ __asm __volatile ("" : "=m" (*spinlock) : "m" (*spinlock));
+}
+
+
+/* The status field of a spinlock is a pointer whose least significant
+ bit is a locked flag.
+
+ Thus the field values have the following meanings:
+
+ status == 0: spinlock is free
+ status == 1: spinlock is taken; no thread is waiting on it
+
+ (status & 1) == 1: spinlock is taken and (status & ~1L) is a
+ pointer to the first waiting thread; other
+ waiting threads are linked via the p_nextlock
+ field.
+ (status & 1) == 0: same as above, but spinlock is not taken.
+
+ 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 internal_function __pthread_lock(struct _pthread_fastlock * lock,
+ pthread_descr self)
+{
+#if defined HAS_COMPARE_AND_SWAP
+ long oldstatus, newstatus;
+ int successful_seizure, spurious_wakeup_count;
+ int spin_count;
+#endif
+
+#if defined TEST_FOR_COMPARE_AND_SWAP
+ if (!__pthread_has_cas)
+#endif
+#if !defined HAS_COMPARE_AND_SWAP || defined TEST_FOR_COMPARE_AND_SWAP
+ {
+ __pthread_acquire(&lock->__spinlock);
+ return;
+ }
+#endif
+
+#if defined HAS_COMPARE_AND_SWAP
+ /* First try it without preparation. Maybe it's a completely
+ uncontested lock. */
+ if (lock->__status == 0 && __compare_and_swap (&lock->__status, 0, 1))
+ return;
+
+ spurious_wakeup_count = 0;
+ spin_count = 0;
+
+ /* On SMP, try spinning to get the lock. */
+#if 0
+ if (__pthread_smp_kernel) {
+ int max_count = lock->__spinlock * 2 + 10;
+
+ if (max_count > MAX_ADAPTIVE_SPIN_COUNT)
+ max_count = MAX_ADAPTIVE_SPIN_COUNT;
+
+ for (spin_count = 0; spin_count < max_count; spin_count++) {
+ if (((oldstatus = lock->__status) & 1) == 0) {
+ if(__compare_and_swap(&lock->__status, oldstatus, oldstatus | 1))
+ {
+ if (spin_count)
+ lock->__spinlock += (spin_count - lock->__spinlock) / 8;
+ READ_MEMORY_BARRIER();
+ return;
+ }
+ }
+#ifdef BUSY_WAIT_NOP
+ BUSY_WAIT_NOP;
+#endif
+ __asm __volatile ("" : "=m" (lock->__status) : "m" (lock->__status));
+ }
+
+ lock->__spinlock += (spin_count - lock->__spinlock) / 8;
+ }
+#endif
+
+again:
+
+ /* No luck, try once more or suspend. */
+
+ do {
+ oldstatus = lock->__status;
+ successful_seizure = 0;
+
+ if ((oldstatus & 1) == 0) {
+ newstatus = oldstatus | 1;
+ successful_seizure = 1;
+ } else {
+ if (self == NULL)
+ self = thread_self();
+ newstatus = (long) self | 1;
+ }
+
+ if (self != NULL) {
+ THREAD_SETMEM(self, p_nextlock, (pthread_descr) (oldstatus));
+ /* Make sure the store in p_nextlock completes before performing
+ the compare-and-swap */
+ MEMORY_BARRIER();
+ }
+ } while(! __compare_and_swap(&lock->__status, oldstatus, newstatus));
+
+ /* Suspend with guard against spurious wakeup.
+ This can happen in pthread_cond_timedwait_relative, when the thread
+ wakes up due to timeout and is still on the condvar queue, and then
+ locks the queue to remove itself. At that point it may still be on the
+ queue, and may be resumed by a condition signal. */
+
+ if (!successful_seizure) {
+ for (;;) {
+ suspend(self);
+ if (self->p_nextlock != NULL) {
+ /* Count resumes that don't belong to us. */
+ spurious_wakeup_count++;
+ continue;
+ }
+ break;
+ }
+ goto again;
+ }
+
+ /* Put back any resumes we caught that don't belong to us. */
+ while (spurious_wakeup_count--)
+ restart(self);
+
+ READ_MEMORY_BARRIER();
+#endif
+}
+
+int __pthread_unlock(struct _pthread_fastlock * lock)
+{
+#if defined HAS_COMPARE_AND_SWAP
+ long oldstatus;
+ pthread_descr thr, * ptr, * maxptr;
+ int maxprio;
+#endif
+
+#if defined TEST_FOR_COMPARE_AND_SWAP
+ if (!__pthread_has_cas)
+#endif
+#if !defined HAS_COMPARE_AND_SWAP || defined TEST_FOR_COMPARE_AND_SWAP
+ {
+ __pthread_release(&lock->__spinlock);
+ return 0;
+ }
+#endif
+
+#if defined HAS_COMPARE_AND_SWAP
+ WRITE_MEMORY_BARRIER();
+
+again:
+ while ((oldstatus = lock->__status) == 1) {
+ if (__compare_and_swap_with_release_semantics(&lock->__status,
+ oldstatus, 0))
+ return 0;
+ }
+
+ /* Find thread in waiting queue with maximal priority */
+ ptr = (pthread_descr *) &lock->__status;
+ thr = (pthread_descr) (oldstatus & ~1L);
+ maxprio = 0;
+ maxptr = ptr;
+
+ /* Before we iterate over the wait queue, we need to execute
+ a read barrier, otherwise we may read stale contents of nodes that may
+ just have been inserted by other processors. One read barrier is enough to
+ ensure we have a stable list; we don't need one for each pointer chase
+ through the list, because we are the owner of the lock; other threads
+ can only add nodes at the front; if a front node is consistent,
+ the ones behind it must also be. */
+
+ READ_MEMORY_BARRIER();
+
+ while (thr != 0) {
+ if (thr->p_priority >= maxprio) {
+ maxptr = ptr;
+ maxprio = thr->p_priority;
+ }
+ ptr = &(thr->p_nextlock);
+ thr = (pthread_descr)((long)(thr->p_nextlock) & ~1L);
+ }
+
+ /* 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. This removal
+ also has the side effect of marking the lock as released
+ because the new status comes from thr->p_nextlock whose
+ least significant bit is clear. */
+ thr = (pthread_descr) (oldstatus & ~1L);
+ if (! __compare_and_swap_with_release_semantics
+ (&lock->__status, oldstatus, (long)(thr->p_nextlock) & ~1L))
+ goto again;
+ } else {
+ /* No risk of concurrent access, remove max prio thread normally.
+ But in this case we must also flip the least significant bit
+ of the status to mark the lock as released. */
+ thr = (pthread_descr)((long)*maxptr & ~1L);
+ *maxptr = thr->p_nextlock;
+
+ /* Ensure deletion from linked list completes before we
+ release the lock. */
+ WRITE_MEMORY_BARRIER();
+
+ do {
+ oldstatus = lock->__status;
+ } while (!__compare_and_swap_with_release_semantics(&lock->__status,
+ oldstatus, oldstatus & ~1L));
+ }
+
+ /* Wake up the selected waiting thread. Woken thread can check
+ its own p_nextlock field for NULL to detect that it has been removed. No
+ barrier is needed here, since restart() and suspend() take
+ care of memory synchronization. */
+
+ thr->p_nextlock = NULL;
+ restart(thr);
+
+ return 0;
+#endif
+}
+
+/*
+ * Alternate fastlocks do not queue threads directly. Instead, they queue
+ * these wait queue node structures. When a timed wait wakes up due to
+ * a timeout, it can leave its wait node in the queue (because there
+ * is no safe way to remove from the quue). Some other thread will
+ * deallocate the abandoned node.
+ */
+
+
+struct wait_node {
+ struct wait_node *next; /* Next node in null terminated linked list */
+ pthread_descr thr; /* The thread waiting with this node */
+ int abandoned; /* Atomic flag */
+};
+
+static long wait_node_free_list;
+static int wait_node_free_list_spinlock;
+
+/* Allocate a new node from the head of the free list using an atomic
+ operation, or else using malloc if that list is empty. A fundamental
+ assumption here is that we can safely access wait_node_free_list->next.
+ That's because we never free nodes once we allocate them, so a pointer to a
+ node remains valid indefinitely. */
+
+static struct wait_node *wait_node_alloc(void)
+{
+ struct wait_node *new_node = 0;
+
+ __pthread_acquire(&wait_node_free_list_spinlock);
+ if (wait_node_free_list != 0) {
+ new_node = (struct wait_node *) wait_node_free_list;
+ wait_node_free_list = (long) new_node->next;
+ }
+ WRITE_MEMORY_BARRIER();
+ __pthread_release(&wait_node_free_list_spinlock);
+
+ if (new_node == 0)
+ return malloc(sizeof *wait_node_alloc());
+
+ return new_node;
+}
+
+/* Return a node to the head of the free list using an atomic
+ operation. */
+
+static void wait_node_free(struct wait_node *wn)
+{
+ __pthread_acquire(&wait_node_free_list_spinlock);
+ wn->next = (struct wait_node *) wait_node_free_list;
+ wait_node_free_list = (long) wn;
+ WRITE_MEMORY_BARRIER();
+ __pthread_release(&wait_node_free_list_spinlock);
+ return;
+}
+
+#if defined HAS_COMPARE_AND_SWAP
+
+/* Remove a wait node from the specified queue. It is assumed
+ that the removal takes place concurrently with only atomic insertions at the
+ head of the queue. */
+
+static void wait_node_dequeue(struct wait_node **pp_head,
+ struct wait_node **pp_node,
+ struct wait_node *p_node)
+{
+ /* If the node is being deleted from the head of the
+ list, it must be deleted using atomic compare-and-swap.
+ Otherwise it can be deleted in the straightforward way. */
+
+ if (pp_node == pp_head) {
+ /* We don't need a read barrier between these next two loads,
+ because it is assumed that the caller has already ensured
+ the stability of *p_node with respect to p_node. */
+
+ long oldvalue = (long) p_node;
+ long newvalue = (long) p_node->next;
+
+ if (__compare_and_swap((long *) pp_node, oldvalue, newvalue))
+ return;
+
+ /* Oops! Compare and swap failed, which means the node is
+ no longer first. We delete it using the ordinary method. But we don't
+ know the identity of the node which now holds the pointer to the node
+ being deleted, so we must search from the beginning. */
+
+ for (pp_node = pp_head; p_node != *pp_node; ) {
+ pp_node = &(*pp_node)->next;
+ READ_MEMORY_BARRIER(); /* Stabilize *pp_node for next iteration. */
+ }
+ }
+
+ *pp_node = p_node->next;
+ return;
+}
+
+#endif
+
+void __pthread_alt_lock(struct _pthread_fastlock * lock,
+ pthread_descr self)
+{
+#if defined HAS_COMPARE_AND_SWAP
+ long oldstatus, newstatus;
+#endif
+ struct wait_node wait_node;
+
+#if defined TEST_FOR_COMPARE_AND_SWAP
+ if (!__pthread_has_cas)
+#endif
+#if !defined HAS_COMPARE_AND_SWAP || defined TEST_FOR_COMPARE_AND_SWAP
+ {
+ int suspend_needed = 0;
+ __pthread_acquire(&lock->__spinlock);
+
+ if (lock->__status == 0)
+ lock->__status = 1;
+ else {
+ if (self == NULL)
+ self = thread_self();
+
+ wait_node.abandoned = 0;
+ wait_node.next = (struct wait_node *) lock->__status;
+ wait_node.thr = self;
+ lock->__status = (long) &wait_node;
+ suspend_needed = 1;
+ }
+
+ __pthread_release(&lock->__spinlock);
+
+ if (suspend_needed)
+ suspend (self);
+ return;
+ }
+#endif
+
+#if defined HAS_COMPARE_AND_SWAP
+ do {
+ oldstatus = lock->__status;
+ if (oldstatus == 0) {
+ newstatus = 1;
+ } else {
+ if (self == NULL)
+ self = thread_self();
+ wait_node.thr = self;
+ newstatus = (long) &wait_node;
+ }
+ wait_node.abandoned = 0;
+ wait_node.next = (struct wait_node *) oldstatus;
+ /* Make sure the store in wait_node.next completes before performing
+ the compare-and-swap */
+ MEMORY_BARRIER();
+ } while(! __compare_and_swap(&lock->__status, oldstatus, newstatus));
+
+ /* Suspend. Note that unlike in __pthread_lock, we don't worry
+ here about spurious wakeup. That's because this lock is not
+ used in situations where that can happen; the restart can
+ only come from the previous lock owner. */
+
+ if (oldstatus != 0)
+ suspend(self);
+
+ READ_MEMORY_BARRIER();
+#endif
+}
+
+/* Timed-out lock operation; returns 0 to indicate timeout. */
+
+int __pthread_alt_timedlock(struct _pthread_fastlock * lock,
+ pthread_descr self, const struct timespec *abstime)
+{
+ long oldstatus = 0;
+#if defined HAS_COMPARE_AND_SWAP
+ long newstatus;
+#endif
+ struct wait_node *p_wait_node = wait_node_alloc();
+
+ /* Out of memory, just give up and do ordinary lock. */
+ if (p_wait_node == 0) {
+ __pthread_alt_lock(lock, self);
+ return 1;
+ }
+
+#if defined TEST_FOR_COMPARE_AND_SWAP
+ if (!__pthread_has_cas)
+#endif
+#if !defined HAS_COMPARE_AND_SWAP || defined TEST_FOR_COMPARE_AND_SWAP
+ {
+ __pthread_acquire(&lock->__spinlock);
+
+ if (lock->__status == 0)
+ lock->__status = 1;
+ else {
+ if (self == NULL)
+ self = thread_self();
+
+ p_wait_node->abandoned = 0;
+ p_wait_node->next = (struct wait_node *) lock->__status;
+ p_wait_node->thr = self;
+ lock->__status = (long) p_wait_node;
+ oldstatus = 1; /* force suspend */
+ }
+
+ __pthread_release(&lock->__spinlock);
+ goto suspend;
+ }
+#endif
+
+#if defined HAS_COMPARE_AND_SWAP
+ do {
+ oldstatus = lock->__status;
+ if (oldstatus == 0) {
+ newstatus = 1;
+ } else {
+ if (self == NULL)
+ self = thread_self();
+ p_wait_node->thr = self;
+ newstatus = (long) p_wait_node;
+ }
+ p_wait_node->abandoned = 0;
+ p_wait_node->next = (struct wait_node *) oldstatus;
+ /* Make sure the store in wait_node.next completes before performing
+ the compare-and-swap */
+ MEMORY_BARRIER();
+ } while(! __compare_and_swap(&lock->__status, oldstatus, newstatus));
+#endif
+
+#if !defined HAS_COMPARE_AND_SWAP || defined TEST_FOR_COMPARE_AND_SWAP
+ suspend:
+#endif
+
+ /* If we did not get the lock, do a timed suspend. If we wake up due
+ to a timeout, then there is a race; the old lock owner may try
+ to remove us from the queue. This race is resolved by us and the owner
+ doing an atomic testandset() to change the state of the wait node from 0
+ to 1. If we succeed, then it's a timeout and we abandon the node in the
+ queue. If we fail, it means the owner gave us the lock. */
+
+ if (oldstatus != 0) {
+ if (timedsuspend(self, abstime) == 0) {
+ if (!testandset(&p_wait_node->abandoned))
+ return 0; /* Timeout! */
+
+ /* Eat oustanding resume from owner, otherwise wait_node_free() below
+ will race with owner's wait_node_dequeue(). */
+ suspend(self);
+ }
+ }
+
+ wait_node_free(p_wait_node);
+
+ READ_MEMORY_BARRIER();
+
+ return 1; /* Got the lock! */
+}
+
+void __pthread_alt_unlock(struct _pthread_fastlock *lock)
+{
+ struct wait_node *p_node, **pp_node, *p_max_prio, **pp_max_prio;
+ struct wait_node ** const pp_head = (struct wait_node **) &lock->__status;
+ int maxprio;
+
+ WRITE_MEMORY_BARRIER();
+
+#if defined TEST_FOR_COMPARE_AND_SWAP
+ if (!__pthread_has_cas)
+#endif
+#if !defined HAS_COMPARE_AND_SWAP || defined TEST_FOR_COMPARE_AND_SWAP
+ {
+ __pthread_acquire(&lock->__spinlock);
+ }
+#endif
+
+ while (1) {
+
+ /* If no threads are waiting for this lock, try to just
+ atomically release it. */
+#if defined TEST_FOR_COMPARE_AND_SWAP
+ if (!__pthread_has_cas)
+#endif
+#if !defined HAS_COMPARE_AND_SWAP || defined TEST_FOR_COMPARE_AND_SWAP
+ {
+ if (lock->__status == 0 || lock->__status == 1) {
+ lock->__status = 0;
+ break;
+ }
+ }
+#endif
+
+#if defined TEST_FOR_COMPARE_AND_SWAP
+ else
+#endif
+
+#if defined HAS_COMPARE_AND_SWAP
+ {
+ long oldstatus = lock->__status;
+ if (oldstatus == 0 || oldstatus == 1) {
+ if (__compare_and_swap_with_release_semantics (&lock->__status, oldstatus, 0))
+ break;
+ else
+ continue;
+ }
+ }
+#endif
+
+ /* Process the entire queue of wait nodes. Remove all abandoned
+ wait nodes and put them into the global free queue, and
+ remember the one unabandoned node which refers to the thread
+ having the highest priority. */
+
+ pp_max_prio = pp_node = pp_head;
+ p_max_prio = p_node = *pp_head;
+ maxprio = INT_MIN;
+
+ READ_MEMORY_BARRIER(); /* Prevent access to stale data through p_node */
+
+ while (p_node != (struct wait_node *) 1) {
+ int prio;
+
+ if (p_node->abandoned) {
+ /* Remove abandoned node. */
+#if defined TEST_FOR_COMPARE_AND_SWAP
+ if (!__pthread_has_cas)
+#endif
+#if !defined HAS_COMPARE_AND_SWAP || defined TEST_FOR_COMPARE_AND_SWAP
+ *pp_node = p_node->next;
+#endif
+#if defined TEST_FOR_COMPARE_AND_SWAP
+ else
+#endif
+#if defined HAS_COMPARE_AND_SWAP
+ wait_node_dequeue(pp_head, pp_node, p_node);
+#endif
+ wait_node_free(p_node);
+ /* Note that the next assignment may take us to the beginning
+ of the queue, to newly inserted nodes, if pp_node == pp_head.
+ In that case we need a memory barrier to stabilize the first of
+ these new nodes. */
+ p_node = *pp_node;
+ if (pp_node == pp_head)
+ READ_MEMORY_BARRIER(); /* No stale reads through p_node */
+ continue;
+ } else if ((prio = p_node->thr->p_priority) >= maxprio) {
+ /* Otherwise remember it if its thread has a higher or equal priority
+ compared to that of any node seen thus far. */
+ maxprio = prio;
+ pp_max_prio = pp_node;
+ p_max_prio = p_node;
+ }
+
+ /* This canno6 jump backward in the list, so no further read
+ barrier is needed. */
+ pp_node = &p_node->next;
+ p_node = *pp_node;
+ }
+
+ /* If all threads abandoned, go back to top */
+ if (maxprio == INT_MIN)
+ continue;
+
+ ASSERT (p_max_prio != (struct wait_node *) 1);
+
+ /* Now we want to to remove the max priority thread's wait node from
+ the list. Before we can do this, we must atomically try to change the
+ node's abandon state from zero to nonzero. If we succeed, that means we
+ have the node that we will wake up. If we failed, then it means the
+ thread timed out and abandoned the node in which case we repeat the
+ whole unlock operation. */
+
+ if (!testandset(&p_max_prio->abandoned)) {
+#if defined TEST_FOR_COMPARE_AND_SWAP
+ if (!__pthread_has_cas)
+#endif
+#if !defined HAS_COMPARE_AND_SWAP || defined TEST_FOR_COMPARE_AND_SWAP
+ *pp_max_prio = p_max_prio->next;
+#endif
+#if defined TEST_FOR_COMPARE_AND_SWAP
+ else
+#endif
+#if defined HAS_COMPARE_AND_SWAP
+ wait_node_dequeue(pp_head, pp_max_prio, p_max_prio);
+#endif
+ restart(p_max_prio->thr);
+ break;
+ }
+ }
+
+#if defined TEST_FOR_COMPARE_AND_SWAP
+ if (!__pthread_has_cas)
+#endif
+#if !defined HAS_COMPARE_AND_SWAP || defined TEST_FOR_COMPARE_AND_SWAP
+ {
+ __pthread_release(&lock->__spinlock);
+ }
+#endif
+}
+
+
+/* Compare-and-swap emulation with a spinlock */
+
+#ifdef TEST_FOR_COMPARE_AND_SWAP
+int __pthread_has_cas = 0;
+#endif
+
+#if !defined HAS_COMPARE_AND_SWAP || defined TEST_FOR_COMPARE_AND_SWAP
+
+int __pthread_compare_and_swap(long * ptr, long oldval, long newval,
+ int * spinlock)
+{
+ int res;
+
+ __pthread_acquire(spinlock);
+
+ if (*ptr == oldval) {
+ *ptr = newval; res = 1;
+ } else {
+ res = 0;
+ }
+
+ __pthread_release(spinlock);
+
+ return res;
+}
+
+#endif
+
+/* The retry strategy is as follows:
+ - We test and set the spinlock MAX_SPIN_COUNT times, calling
+ sched_yield() each time. This gives ample opportunity for other
+ threads with priority >= our priority to make progress and
+ release the spinlock.
+ - If a thread with priority < our priority owns the spinlock,
+ calling sched_yield() repeatedly is useless, since we're preventing
+ the owning thread from making progress and releasing the spinlock.
+ So, after MAX_SPIN_LOCK attemps, we suspend the calling thread
+ using nanosleep(). This again should give time to the owning thread
+ for releasing the spinlock.
+ Notice that the nanosleep() interval must not be too small,
+ since the kernel does busy-waiting for short intervals in a realtime
+ process (!). The smallest duration that guarantees thread
+ suspension is currently 2ms.
+ - When nanosleep() returns, we try again, doing MAX_SPIN_COUNT
+ sched_yield(), then sleeping again if needed. */
+
+static void __pthread_acquire(int * spinlock)
+{
+ int cnt = 0;
+ struct timespec tm;
+
+ READ_MEMORY_BARRIER();
+
+ while (testandset(spinlock)) {
+ if (cnt < MAX_SPIN_COUNT) {
+ sched_yield();
+ cnt++;
+ } else {
+ tm.tv_sec = 0;
+ tm.tv_nsec = SPIN_SLEEP_DURATION;
+ nanosleep(&tm, NULL);
+ cnt = 0;
+ }
+ }
+}