urcu_defer: Use cancellation flag instead of pthread_cancel()

- Provides better control over cancellation point location.
- Set the futex to 0 before exiting the defer thread.

This patch combines and enhances patches from Lai Jiangshan:
  urcu,defer_rcu: fix missing respond to a cancellation request
  urcu,defer_rcu: Avoid thread exit unexpected

Reported-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/urcu-defer-impl.h b/urcu-defer-impl.h
index d1ab0466096e5ebccc594658e843eab25d55dac7..4211f7c76954c2fc1bfd088ac0497cb2a34516a9 100644 (file)
--- a/urcu-defer-impl.h
+++ b/urcu-defer-impl.h
@@ -122,6 +122,7 @@ static pthread_mutex_t rcu_defer_mutex = PTHREAD_MUTEX_INITIALIZER;
 static pthread_mutex_t defer_thread_mutex = PTHREAD_MUTEX_INITIALIZER;
 
 static int32_t defer_thread_futex;
+static int32_t defer_thread_stop;
 
 /*
  * Written to only by each individual deferer. Read by both the deferer and
@@ -148,7 +149,6 @@ static void mutex_lock_defer(pthread_mutex_t *mutex)
                        perror("Error in pthread mutex lock");
                        exit(-1);
                }
-               pthread_testcancel();
                poll(NULL,0,10);
        }
 #endif /* #else #ifndef DISTRUST_SIGNALS_EXTREME */
@@ -186,7 +186,13 @@ static unsigned long rcu_defer_num_callbacks(void)
 static void wait_defer(void)
 {
        uatomic_dec(&defer_thread_futex);
-       cmm_smp_mb();   /* Write futex before read queue */
+       /* Write futex before read queue */
+       /* Write futex before read defer_thread_stop */
+       cmm_smp_mb();
+       if (_CMM_LOAD_SHARED(defer_thread_stop)) {
+               uatomic_set(&defer_thread_futex, 0);
+               pthread_exit(0);
+       }
        if (rcu_defer_num_callbacks()) {
                cmm_smp_mb();   /* Read queue before write futex */
                /* Callbacks are queued, don't wait. */
@@ -359,7 +365,6 @@ void _defer_rcu(void (*fct)(void *p), void *p)
 void *thr_defer(void *args)
 {
        for (;;) {
-               pthread_testcancel();
                /*
                 * "Be green". Don't wake up the CPU if there is no RCU work
                 * to perform whatsoever. Aims at saving laptop battery life by
@@ -396,10 +401,17 @@ static void stop_defer_thread(void)
        int ret;
        void *tret;
 
-       pthread_cancel(tid_defer);
+       _CMM_STORE_SHARED(defer_thread_stop, 1);
+       /* Store defer_thread_stop before testing futex */
+       cmm_smp_mb();
        wake_up_defer();
+
        ret = pthread_join(tid_defer, &tret);
        assert(!ret);
+
+       CMM_STORE_SHARED(defer_thread_stop, 0);
+       /* defer thread should always exit when futex value is 0 */
+       assert(uatomic_read(&defer_thread_futex) == 0);
 }
 
 int rcu_defer_register_thread(void)