This patch modifies the fallback implementation of the POSIX spin-locks
so that the unlock operation verifies that the lock is indeed locked.
2020-07-01 Bruno Haible <br...@clisp.org>
pthread-spin: Add error checking.
* lib/pthread-spin.c: Include <stdbool.h>.
(pthread_spin_init, pthread_spin_lock, pthread_spin_trylock,
pthread_spin_unlock) [GCC>=4.7]: Prefer an implementation that verifies
the unlocks.
* modules/pthread-spin (Depends-on): Add stdbool.
diff --git a/lib/pthread-spin.c b/lib/pthread-spin.c
index 93e8b37..73eb9f3 100644
--- a/lib/pthread-spin.c
+++ b/lib/pthread-spin.c
@@ -21,6 +21,8 @@
/* Specification. */
#include <pthread.h>
+#include <stdbool.h>
+
#if (defined _WIN32 && ! defined __CYGWIN__) && USE_WINDOWS_THREADS
# include "windows-spin.h"
#endif
@@ -72,6 +74,55 @@ pthread_spin_destroy (pthread_spinlock_t *lock)
Documentation:
<https://gcc.gnu.org/onlinedocs/gcc-4.7.0/gcc/_005f_005fatomic-Builtins.html>
*/
+# if 1
+/* An implementation that verifies the unlocks. */
+
+int
+pthread_spin_init (pthread_spinlock_t *lock,
+ int shared_across_processes _GL_UNUSED)
+{
+ __atomic_store_n ((char *) lock, 0, __ATOMIC_SEQ_CST);
+ return 0;
+}
+
+int
+pthread_spin_lock (pthread_spinlock_t *lock)
+{
+ /* Wait until *lock becomes 0, then replace it with 1. */
+ asyncsafe_spinlock_t zero;
+ while (!(zero = 0,
+ __atomic_compare_exchange_n ((char *) lock, &zero, 1, false,
+ __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST)))
+ ;
+ return 0;
+}
+
+int
+pthread_spin_trylock (pthread_spinlock_t *lock)
+{
+ asyncsafe_spinlock_t zero;
+ if (!(zero = 0,
+ __atomic_compare_exchange_n ((char *) lock, &zero, 1, false,
+ __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST)))
+ return EBUSY;
+ return 0;
+}
+
+int
+pthread_spin_unlock (pthread_spinlock_t *lock)
+{
+ /* If *lock is 1, then replace it with 0. */
+ asyncsafe_spinlock_t one = 1;
+ if (!__atomic_compare_exchange_n ((char *) lock, &one, 0, false,
+ __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST))
+ abort ();
+ return 0;
+}
+
+# else
+/* An implementation that is a little bit more optimized, but does not verify
+ the unlocks. */
+
int
pthread_spin_init (pthread_spinlock_t *lock,
int shared_across_processes _GL_UNUSED)
@@ -103,6 +154,8 @@ pthread_spin_unlock (pthread_spinlock_t *lock)
return 0;
}
+# endif
+
int
pthread_spin_destroy (pthread_spinlock_t *lock)
{
diff --git a/modules/pthread-spin b/modules/pthread-spin
index 53e0051..ce69944 100644
--- a/modules/pthread-spin
+++ b/modules/pthread-spin
@@ -7,6 +7,7 @@ m4/pthread-spin.m4
Depends-on:
pthread-h
+stdbool [test $HAVE_PTHREAD_SPIN_INIT = 0 || test
$REPLACE_PTHREAD_SPIN_INIT = 1]
windows-spin [test $gl_threads_api = windows]
configure.ac:
