wfqueue: provide API for caller-locked dequeue

[urcu.git] / urcu-bp.c

diff --git a/urcu-bp.c b/urcu-bp.c
index eda000539b19b01ce582fe098be1d1cc0f1a3b3f..61d42fa20188d6b12ab3a560cede576828a77099 100644 (file)
--- a/urcu-bp.c
+++ b/urcu-bp.c
@@ -3,7 +3,7 @@
  *
  * Userspace RCU library, "bulletproof" version.
  *
- * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
+ * Copyright (c) 2009 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
  * Copyright (c) 2009 Paul E. McKenney, IBM Corporation.
  *
  * This library is free software; you can redistribute it and/or
@@ -116,30 +116,37 @@ static void mutex_unlock(pthread_mutex_t *mutex)
        }
 }
 
-/*
- * called with rcu_gp_lock held.
- */
-static void switch_next_rcu_qparity(void)
-{
-       STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);
-}
-
-void wait_for_quiescent_state(void)
+void update_counter_and_wait(void)
 {
        LIST_HEAD(qsreaders);
        int wait_loops = 0;
        struct rcu_reader *index, *tmp;
 
-       if (list_empty(&registry))
-               return;
+       /* Switch parity: 0 -> 1, 1 -> 0 */
+       STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR_PHASE);
+
+       /*
+        * Must commit qparity update to memory before waiting for other parity
+        * quiescent state. Failure to do so could result in the writer waiting
+        * forever while new readers are always accessing data (no progress).
+        * Ensured by STORE_SHARED and LOAD_SHARED.
+        */
+
+       /*
+        * Adding a smp_mb() which is _not_ formally required, but makes the
+        * model easier to understand. It does not have a big performance impact
+        * anyway, given this is the write-side.
+        */
+       smp_mb();
+
        /*
         * Wait for each thread rcu_reader.ctr count to become 0.
         */
        for (;;) {
                wait_loops++;
-               list_for_each_entry_safe(index, tmp, &registry, head) {
+               list_for_each_entry_safe(index, tmp, &registry, node) {
                        if (!rcu_old_gp_ongoing(&index->ctr))
-                               list_move(&index->head, &qsreaders);
+                               list_move(&index->node, &qsreaders);
                }
 
                if (list_empty(&registry)) {
@@ -167,44 +174,21 @@ void synchronize_rcu(void)
 
        mutex_lock(&rcu_gp_lock);
 
-       /* Remove old registry elements */
-       rcu_gc_registry();
+       if (list_empty(&registry))
+               goto out;
 
        /* All threads should read qparity before accessing data structure
-        * where new ptr points to. Must be done within rcu_gp_lock because it
-        * iterates on reader threads.*/
+        * where new ptr points to. */
        /* Write new ptr before changing the qparity */
        smp_mb();
 
-       switch_next_rcu_qparity();      /* 0 -> 1 */
-
-       /*
-        * 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).
-        * Ensured by STORE_SHARED and LOAD_SHARED.
-        */
-
-       /*
-        * Adding a smp_mb() which is _not_ formally required, but makes the
-        * model easier to understand. It does not have a big performance impact
-        * anyway, given this is the write-side.
-        */
-       smp_mb();
+       /* Remove old registry elements */
+       rcu_gc_registry();
 
        /*
         * Wait for previous parity to be empty of readers.
         */
-       wait_for_quiescent_state();     /* Wait readers in parity 0 */
-
-       /*
-        * 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).
-        * Ensured by STORE_SHARED and LOAD_SHARED.
-        */
+       update_counter_and_wait();      /* 0 -> 1, wait readers in parity 0 */
 
        /*
         * Adding a smp_mb() which is _not_ formally required, but makes the
@@ -213,33 +197,17 @@ void synchronize_rcu(void)
         */
        smp_mb();
 
-       switch_next_rcu_qparity();      /* 1 -> 0 */
-
        /*
-        * 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).
-        * Ensured by STORE_SHARED and LOAD_SHARED.
-        */
-
-       /*
-        * Adding a smp_mb() which is _not_ formally required, but makes the
-        * model easier to understand. It does not have a big performance impact
-        * anyway, given this is the write-side.
+        * Wait for previous parity to be empty of readers.
         */
-       smp_mb();
+       update_counter_and_wait();      /* 1 -> 0, wait readers in parity 1 */
 
        /*
-        * Wait for previous parity to be empty of readers.
+        * Finish waiting for reader threads before letting the old ptr being
+        * freed.
         */
-       wait_for_quiescent_state();     /* Wait readers in parity 1 */
-
-       /* Finish waiting for reader threads before letting the old ptr being
-        * freed. Must be done within rcu_gp_lock because it iterates on reader
-        * threads. */
        smp_mb();
-
+out:
        mutex_unlock(&rcu_gp_lock);
        ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
        assert(!ret);
@@ -311,7 +279,7 @@ static void add_thread(void)
        /* Add to registry */
        rcu_reader_reg->tid = pthread_self();
        assert(rcu_reader_reg->ctr == 0);
-       list_add(&rcu_reader_reg->head, &registry);
+       list_add(&rcu_reader_reg->node, &registry);
        rcu_reader = rcu_reader_reg;
 }
 
@@ -331,7 +299,8 @@ static void rcu_gc_registry(void)
                ret = pthread_kill(tid, 0);
                assert(ret != EINVAL);
                if (ret == ESRCH) {
-                       list_del(&rcu_reader_reg->head);
+                       list_del(&rcu_reader_reg->node);
+                       rcu_reader_reg->ctr = 0;
                        rcu_reader_reg->alloc = 0;
                        registry_arena.used -= sizeof(struct rcu_reader);
                }