Add Promela model

[urcu.git] / urcu.c

diff --git a/urcu.c b/urcu.c
index 23a985b9f9f4cdaf992c227322720e38bc139d85..9542b264a6dbf53d36d2fb63e7578b4e7ff2b2f5 100644 (file)
--- a/urcu.c
+++ b/urcu.c
@@ -19,17 +19,21 @@
 
 pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
 
-/* Global grace period counter */
-int urcu_gp_ctr;
+/*
+ * Global grace period counter.
+ * Contains the current RCU_GP_CTR_BIT.
+ * Also has a RCU_GP_CTR_BIT of 1, to accelerate the reader fast path.
+ */
+long urcu_gp_ctr = RCU_GP_COUNT;
 
-int __thread urcu_active_readers;
+long __thread urcu_active_readers;
 
 /* Thread IDs of registered readers */
 #define INIT_NUM_THREADS 4
 
 struct reader_data {
        pthread_t tid;
-       int *urcu_active_readers;
+       long *urcu_active_readers;
 };
 
 #ifdef DEBUG_YIELD
@@ -70,6 +74,12 @@ static void switch_next_urcu_qparity(void)
        urcu_gp_ctr ^= RCU_GP_CTR_BIT;
 }
 
+#ifdef DEBUG_FULL_MB
+static void force_mb_all_threads(void)
+{
+       mb();
+}
+#else
 static void force_mb_all_threads(void)
 {
        struct reader_data *index;
@@ -98,6 +108,7 @@ static void force_mb_all_threads(void)
        mb();   /* read sig_done before ending the barrier */
        debug_yield_write();
 }
+#endif
 
 void wait_for_quiescent_state(void)
 {
@@ -114,77 +125,70 @@ void wait_for_quiescent_state(void)
                while (rcu_old_gp_ongoing(index->urcu_active_readers))
                        barrier();
        }
-       /*
-        * Locally : read *index->urcu_active_readers before freeing old
-        * pointer.
-        * Remote (reader threads) : Order urcu_qparity update and other
-        * thread's quiescent state counter read.
-        */
-       force_mb_all_threads();
 }
 
-static void switch_qparity(void)
+void synchronize_rcu(void)
 {
-       /* All threads should read qparity before accessing data structure. */
-       /* Write ptr before changing the qparity */
+       /* All threads should read qparity before accessing data structure
+        * where new ptr points to. */
+       /* Write new ptr before changing the qparity */
        force_mb_all_threads();
        debug_yield_write();
-       switch_next_urcu_qparity();
+
+       internal_urcu_lock();
+       debug_yield_write();
+
+       switch_next_urcu_qparity();     /* 0 -> 1 */
        debug_yield_write();
 
        /*
-        * Wait for previous parity to be empty of readers.
+        * Must commit qparity update to memory before waiting for parity
+        * 0 quiescent state. Failure to do so could result in the writer
+        * waiting forever while new readers are always accessing data (no
+        * progress).
         */
-       wait_for_quiescent_state();
-}
+       mb();
 
-void synchronize_rcu(void)
-{
-       debug_yield_write();
-       internal_urcu_lock();
-       debug_yield_write();
-       switch_qparity();
-       debug_yield_write();
-       switch_qparity();
-       debug_yield_write();
-       internal_urcu_lock();
+       /*
+        * Wait for previous parity to be empty of readers.
+        */
+       wait_for_quiescent_state();     /* Wait readers in parity 0 */
        debug_yield_write();
-}
 
-/*
- * Return old pointer, OK to free, no more reference exist.
- * Called under rcu_write_lock.
- */
-void *urcu_publish_content(void **ptr, void *new)
-{
-       void *oldptr;
+       /*
+        * Must finish waiting for quiescent state for parity 0 before
+        * committing qparity update to memory. Failure to do so could result in
+        * the writer waiting forever while new readers are always accessing
+        * data (no progress).
+        */
+       mb();
 
+       switch_next_urcu_qparity();     /* 1 -> 0 */
        debug_yield_write();
-       internal_urcu_lock();
-       debug_yield_write();
+
        /*
-        * We can publish the new pointer before we change the current qparity.
-        * Readers seeing the new pointer while being in the previous qparity
-        * window will make us wait until the end of the quiescent state before
-        * we release the unrelated memory area. However, given we hold the
-        * urcu_mutex, we are making sure that no further garbage collection can
-        * occur until we release the mutex, therefore we guarantee that this
-        * given reader will have completed its execution using the new pointer
-        * when the next quiescent state window will be over.
+        * Must commit qparity update to memory before waiting for parity
+        * 1 quiescent state. Failure to do so could result in the writer
+        * waiting forever while new readers are always accessing data (no
+        * progress).
         */
-       oldptr = *ptr;
-       debug_yield_write();
-       rcu_assign_pointer(*ptr, new);
+       mb();
 
+       /*
+        * Wait for previous parity to be empty of readers.
+        */
+       wait_for_quiescent_state();     /* Wait readers in parity 1 */
        debug_yield_write();
-       switch_qparity();
-       debug_yield_write();
-       switch_qparity();
-       debug_yield_write();
+
        internal_urcu_unlock();
        debug_yield_write();
 
-       return oldptr;
+       /* All threads should finish using the data referred to by old ptr
+        * before decrementing their urcu_active_readers count */
+       /* Finish waiting for reader threads before letting the old ptr being
+        * freed. */
+       force_mb_all_threads();
+       debug_yield_write();
 }
 
 void urcu_add_reader(pthread_t id)
@@ -249,6 +253,7 @@ void urcu_unregister_thread(void)
        internal_urcu_unlock();
 }
 
+#ifndef DEBUG_FULL_MB
 void sigurcu_handler(int signo, siginfo_t *siginfo, void *context)
 {
        mb();
@@ -281,3 +286,4 @@ void __attribute__((destructor)) urcu_exit(void)
        assert(act.sa_sigaction == sigurcu_handler);
        free(reader_data);
 }
+#endif