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-rw-r--r--ChangeLog8
-rw-r--r--tests/test-lock.c55
2 files changed, 59 insertions, 4 deletions
diff --git a/ChangeLog b/ChangeLog
index 11b8eaa..ebd491f 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -15,6 +15,14 @@
2017-01-05 Bruno Haible <bruno@clisp.org>
+ lock tests: Prefer semaphore over mutex.
+ * tests/test-lock.c (USE_SEMAPHORE): New constant.
+ (struct atomic_int, init_atomic_int, get_atomic_int_value,
+ set_atomic_int_value) [USE_SEMAPHORE]: Define using a POSIX semaphore.
+ Suggested by Torvald Riegel <triegel@redhat.com>.
+
+2017-01-05 Bruno Haible <bruno@clisp.org>
+
lock: Provide guarantee to avoid writer starvation for rwlocks.
The rationale is: 1) Read-preferring read-write locks are prone to
writer starvation if the number of reader threads multiplied by the
diff --git a/tests/test-lock.c b/tests/test-lock.c
index 095511e..f3da4cc 100644
--- a/tests/test-lock.c
+++ b/tests/test-lock.c
@@ -51,12 +51,20 @@
#define EXPLICIT_YIELD 1
/* Whether to use 'volatile' on some variables that communicate information
- between threads. If set to 0, a lock is used to protect these variables.
- If set to 1, 'volatile' is used; this is theoretically equivalent but can
- lead to much slower execution (e.g. 30x slower total run time on a 40-core
- machine. */
+ between threads. If set to 0, a semaphore or a lock is used to protect
+ these variables. If set to 1, 'volatile' is used; this is theoretically
+ equivalent but can lead to much slower execution (e.g. 30x slower total
+ run time on a 40-core machine), because 'volatile' does not imply any
+ synchronization/communication between different CPUs. */
#define USE_VOLATILE 0
+#if USE_POSIX_THREADS
+/* Whether to use a semaphore to communicate information between threads.
+ If set to 0, a lock is used. If set to 1, a semaphore is used.
+ Uncomment this to reduce the dependencies of this test. */
+# define USE_SEMAPHORE 1
+#endif
+
/* Whether to print debugging messages. */
#define ENABLE_DEBUGGING 0
@@ -97,6 +105,10 @@
#include "glthread/thread.h"
#include "glthread/yield.h"
+#if USE_SEMAPHORE
+# include <errno.h>
+# include <semaphore.h>
+#endif
#if ENABLE_DEBUGGING
# define dbgprintf printf
@@ -128,6 +140,41 @@ set_atomic_int_value (struct atomic_int *ai, int new_value)
{
ai->value = new_value;
}
+#elif USE_SEMAPHORE
+/* This atomic_int implementation can only support the values 0 and 1.
+ It is initially 0 and can be set to 1 only once. */
+struct atomic_int {
+ sem_t semaphore;
+};
+static void
+init_atomic_int (struct atomic_int *ai)
+{
+ sem_init (&ai->semaphore, 0, 0);
+}
+static int
+get_atomic_int_value (struct atomic_int *ai)
+{
+ if (sem_trywait (&ai->semaphore) == 0)
+ {
+ if (sem_post (&ai->semaphore))
+ abort ();
+ return 1;
+ }
+ else if (errno == EAGAIN)
+ return 0;
+ else
+ abort ();
+}
+static void
+set_atomic_int_value (struct atomic_int *ai, int new_value)
+{
+ if (new_value == 0)
+ /* It's already initialized with 0. */
+ return;
+ /* To set the value 1: */
+ if (sem_post (&ai->semaphore))
+ abort ();
+}
#else
struct atomic_int {
gl_lock_define (, lock)