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-rw-r--r--libpthread/nptl/sysdeps/or1k/pthread_spin_lock.c65
1 files changed, 65 insertions, 0 deletions
diff --git a/libpthread/nptl/sysdeps/or1k/pthread_spin_lock.c b/libpthread/nptl/sysdeps/or1k/pthread_spin_lock.c
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+++ b/libpthread/nptl/sysdeps/or1k/pthread_spin_lock.c
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+/* pthread_spin_lock -- lock a spin lock. Generic version.
+ Copyright (C) 2012-2016 Free Software Foundation, Inc.
+
+ The GNU C Library is free software; you can redistribute it and/or
+ modify it under the terms of the GNU Lesser General Public
+ License as published by the Free Software Foundation; either
+ version 2.1 of the License, or (at your option) any later version.
+
+ The GNU C Library 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
+ Lesser General Public License for more details.
+
+ You should have received a copy of the GNU Lesser General Public
+ License along with the GNU C Library; if not, see
+ <http://www.gnu.org/licenses/>. */
+
+#include <atomic.h>
+#include "pthreadP.h"
+
+/* A machine-specific version can define SPIN_LOCK_READS_BETWEEN_CMPXCHG
+ to the number of plain reads that it's optimal to spin on between uses
+ of atomic_compare_and_exchange_val_acq. If spinning forever is optimal
+ then use -1. If no plain reads here would ever be optimal, use 0. */
+#define SPIN_LOCK_READS_BETWEEN_CMPXCHG 1000
+
+int
+pthread_spin_lock (pthread_spinlock_t *lock)
+{
+ /* atomic_exchange usually takes less instructions than
+ atomic_compare_and_exchange. On the other hand,
+ atomic_compare_and_exchange potentially generates less bus traffic
+ when the lock is locked.
+ We assume that the first try mostly will be successful, and we use
+ atomic_exchange. For the subsequent tries we use
+ atomic_compare_and_exchange. */
+ if (atomic_exchange_acq (lock, 1) == 0)
+ return 0;
+
+ do
+ {
+ /* The lock is contended and we need to wait. Going straight back
+ to cmpxchg is not a good idea on many targets as that will force
+ expensive memory synchronizations among processors and penalize other
+ running threads.
+ On the other hand, we do want to update memory state on the local core
+ once in a while to avoid spinning indefinitely until some event that
+ will happen to update local memory as a side-effect. */
+ if (SPIN_LOCK_READS_BETWEEN_CMPXCHG >= 0)
+ {
+ int wait = SPIN_LOCK_READS_BETWEEN_CMPXCHG;
+
+ while (*lock != 0 && wait > 0)
+ --wait;
+ }
+ else
+ {
+ while (*lock != 0)
+ ;
+ }
+ }
+ while (atomic_compare_and_exchange_val_acq (lock, 1, 0) != 0);
+
+ return 0;
+}