lock test: Fix performance problem on multi-core machines.

* tests/test-lock.c (USE_VOLATILE): New macro.
(struct atomic_int): New type.
(init_atomic_int, get_atomic_int_value, set_atomic_int_value): New
functions.
(lock_checker_done, rwlock_checker_done, reclock_checker_done): Define
as 'struct atomic_int'.
(lock_checker_thread, test_lock, rwlock_checker_thread, test_rwlock,
reclock_checker_thread, test_recursive_lock): Use the new functions.
Reported by Eric Blake in
https://www.redhat.com/archives/libvir-list/2012-March/msg00854.html
and by Pádraig Brady in
http://lists.gnu.org/archive/html/bug-gnulib/2016-12/msg00117.html.

1 files changed, 67 insertions, 12 deletions

diff --git a/tests/test-lock.c b/tests/test-lock.c
index cb734b4e69..aa6de27397 100644
--- a/tests/test-lock.c
+++ b/tests/test-lock.c
@@ -50,6 +50,13 @@
    Uncomment this to see if the operating system has a fair scheduler.  */
 #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.  */
+#define USE_VOLATILE 0
+
 /* Whether to print debugging messages.  */
 #define ENABLE_DEBUGGING 0
 
@@ -103,6 +110,51 @@
 # define yield()
 #endif
 
+#if USE_VOLATILE
+struct atomic_int {
+  volatile int value;
+};
+static void
+init_atomic_int (struct atomic_int *ai)
+{
+}
+static int
+get_atomic_int_value (struct atomic_int *ai)
+{
+  return ai->value;
+}
+static void
+set_atomic_int_value (struct atomic_int *ai, int new_value)
+{
+  ai->value = new_value;
+}
+#else
+struct atomic_int {
+  gl_lock_define (, lock)
+  int value;
+};
+static void
+init_atomic_int (struct atomic_int *ai)
+{
+  gl_lock_init (ai->lock);
+}
+static int
+get_atomic_int_value (struct atomic_int *ai)
+{
+  gl_lock_lock (ai->lock);
+  int ret = ai->value;
+  gl_lock_unlock (ai->lock);
+  return ret;
+}
+static void
+set_atomic_int_value (struct atomic_int *ai, int new_value)
+{
+  gl_lock_lock (ai->lock);
+  ai->value = new_value;
+  gl_lock_unlock (ai->lock);
+}
+#endif
+
 #define ACCOUNT_COUNT 4
 
 static int account[ACCOUNT_COUNT];
@@ -170,12 +222,12 @@ lock_mutator_thread (void *arg)
   return NULL;
 }
 
-static volatile int lock_checker_done;
+static struct atomic_int lock_checker_done;
 
 static void *
 lock_checker_thread (void *arg)
 {
-  while (!lock_checker_done)
+  while (get_atomic_int_value (&lock_checker_done) == 0)
     {
       dbgprintf ("Checker %p before check lock\n", gl_thread_self_pointer ());
       gl_lock_lock (my_lock);
@@ -200,7 +252,8 @@ test_lock (void)
   /* Initialization.  */
   for (i = 0; i < ACCOUNT_COUNT; i++)
     account[i] = 1000;
-  lock_checker_done = 0;
+  init_atomic_int (&lock_checker_done);
+  set_atomic_int_value (&lock_checker_done, 0);
 
   /* Spawn the threads.  */
   checkerthread = gl_thread_create (lock_checker_thread, NULL);
@@ -210,7 +263,7 @@ test_lock (void)
   /* Wait for the threads to terminate.  */
   for (i = 0; i < THREAD_COUNT; i++)
     gl_thread_join (threads[i], NULL);
-  lock_checker_done = 1;
+  set_atomic_int_value (&lock_checker_done, 1);
   gl_thread_join (checkerthread, NULL);
   check_accounts ();
 }
@@ -254,12 +307,12 @@ rwlock_mutator_thread (void *arg)
   return NULL;
 }
 
-static volatile int rwlock_checker_done;
+static struct atomic_int rwlock_checker_done;
 
 static void *
 rwlock_checker_thread (void *arg)
 {
-  while (!rwlock_checker_done)
+  while (get_atomic_int_value (&rwlock_checker_done) == 0)
     {
       dbgprintf ("Checker %p before check rdlock\n", gl_thread_self_pointer ());
       gl_rwlock_rdlock (my_rwlock);
@@ -284,7 +337,8 @@ test_rwlock (void)
   /* Initialization.  */
   for (i = 0; i < ACCOUNT_COUNT; i++)
     account[i] = 1000;
-  rwlock_checker_done = 0;
+  init_atomic_int (&rwlock_checker_done);
+  set_atomic_int_value (&rwlock_checker_done, 0);
 
   /* Spawn the threads.  */
   for (i = 0; i < THREAD_COUNT; i++)
@@ -295,7 +349,7 @@ test_rwlock (void)
   /* Wait for the threads to terminate.  */
   for (i = 0; i < THREAD_COUNT; i++)
     gl_thread_join (threads[i], NULL);
-  rwlock_checker_done = 1;
+  set_atomic_int_value (&rwlock_checker_done, 1);
   for (i = 0; i < THREAD_COUNT; i++)
     gl_thread_join (checkerthreads[i], NULL);
   check_accounts ();
@@ -356,12 +410,12 @@ reclock_mutator_thread (void *arg)
   return NULL;
 }
 
-static volatile int reclock_checker_done;
+static struct atomic_int reclock_checker_done;
 
 static void *
 reclock_checker_thread (void *arg)
 {
-  while (!reclock_checker_done)
+  while (get_atomic_int_value (&reclock_checker_done) == 0)
     {
       dbgprintf ("Checker %p before check lock\n", gl_thread_self_pointer ());
       gl_recursive_lock_lock (my_reclock);
@@ -386,7 +440,8 @@ test_recursive_lock (void)
   /* Initialization.  */
   for (i = 0; i < ACCOUNT_COUNT; i++)
     account[i] = 1000;
-  reclock_checker_done = 0;
+  init_atomic_int (&reclock_checker_done);
+  set_atomic_int_value (&reclock_checker_done, 0);
 
   /* Spawn the threads.  */
   checkerthread = gl_thread_create (reclock_checker_thread, NULL);
@@ -396,7 +451,7 @@ test_recursive_lock (void)
   /* Wait for the threads to terminate.  */
   for (i = 0; i < THREAD_COUNT; i++)
     gl_thread_join (threads[i], NULL);
-  reclock_checker_done = 1;
+  set_atomic_int_value (&reclock_checker_done, 1);
   gl_thread_join (checkerthread, NULL);
   check_accounts ();
 }