X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu-bp.c;h=4dc402865a026800ccef0bb35378be6241c81505;hp=190a5693dff5aaa8ee683faa18f1eeecca9658db;hb=a4922ed92bea8e5552a3e66b7dd7b4721b754c90;hpb=95b94246b745a49ec7e5a33661ef638b0dd2950b

diff --git a/urcu-bp.c b/urcu-bp.c
index 190a569..4dc4028 100644
--- a/urcu-bp.c
+++ b/urcu-bp.c
@@ -79,8 +79,8 @@ void *mremap_wrapper(void *old_address, size_t old_size,
 }
 #endif
 
-/* Sleep delay in us */
-#define RCU_SLEEP_DELAY		1000
+/* Sleep delay in ms */
+#define RCU_SLEEP_DELAY_MS	10
 #define INIT_NR_THREADS		8
 #define ARENA_INIT_ALLOC		\
 	sizeof(struct registry_chunk)	\
@@ -91,14 +91,34 @@ void *mremap_wrapper(void *old_address, size_t old_size,
  */
 #define RCU_QS_ACTIVE_ATTEMPTS 100
 
+static
+int rcu_bp_refcount;
+
+static
+void __attribute__((constructor)) rcu_bp_init(void);
+static
 void __attribute__((destructor)) rcu_bp_exit(void);
 
+/*
+ * rcu_gp_lock ensures mutual exclusion between threads calling
+ * synchronize_rcu().
+ */
 static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER;
+/*
+ * rcu_registry_lock ensures mutual exclusion between threads
+ * registering and unregistering themselves to/from the registry, and
+ * with threads reading that registry from synchronize_rcu(). However,
+ * this lock is not held all the way through the completion of awaiting
+ * for the grace period. It is sporadically released between iterations
+ * on the registry.
+ * rcu_registry_lock may nest inside rcu_gp_lock.
+ */
+static pthread_mutex_t rcu_registry_lock = PTHREAD_MUTEX_INITIALIZER;
 
-#ifdef DEBUG_YIELD
-unsigned int rcu_yield_active;
-DEFINE_URCU_TLS(unsigned int, rcu_rand_yield);
-#endif
+static pthread_mutex_t init_lock = PTHREAD_MUTEX_INITIALIZER;
+static int initialized;
+
+static pthread_key_t urcu_bp_key;
 
 struct rcu_gp rcu_gp = { .ctr = RCU_GP_COUNT };
 
@@ -112,7 +132,7 @@ static CDS_LIST_HEAD(registry);
 
 struct registry_chunk {
 	size_t data_len;		/* data length */
-	size_t used;			/* data used */
+	size_t used;			/* amount of data used */
 	struct cds_list_head node;	/* chunk_list node */
 	char data[];
 };
@@ -128,8 +148,6 @@ static struct registry_arena registry_arena = {
 /* Saved fork signal mask, protected by rcu_gp_lock */
 static sigset_t saved_fork_signal_mask;
 
-static void rcu_gc_registry(void);
-
 static void mutex_lock(pthread_mutex_t *mutex)
 {
 	int ret;
@@ -156,11 +174,15 @@ static void mutex_unlock(pthread_mutex_t *mutex)
 		urcu_die(ret);
 }
 
+/*
+ * Always called with rcu_registry lock held. Releases this lock between
+ * iterations and grabs it again. Holds the lock when it returns.
+ */
 static void wait_for_readers(struct cds_list_head *input_readers,
 			struct cds_list_head *cur_snap_readers,
 			struct cds_list_head *qsreaders)
 {
-	int wait_loops = 0;
+	unsigned int wait_loops = 0;
 	struct rcu_reader *index, *tmp;
 
 	/*
@@ -169,7 +191,9 @@ static void wait_for_readers(struct cds_list_head *input_readers,
 	 * rcu_gp.ctr value.
 	 */
 	for (;;) {
-		wait_loops++;
+		if (wait_loops < RCU_QS_ACTIVE_ATTEMPTS)
+			wait_loops++;
+
 		cds_list_for_each_entry_safe(index, tmp, input_readers, node) {
 			switch (rcu_reader_state(&index->ctr)) {
 			case RCU_READER_ACTIVE_CURRENT:
@@ -196,10 +220,14 @@ static void wait_for_readers(struct cds_list_head *input_readers,
 		if (cds_list_empty(input_readers)) {
 			break;
 		} else {
-			if (wait_loops == RCU_QS_ACTIVE_ATTEMPTS)
-				usleep(RCU_SLEEP_DELAY);
+			/* Temporarily unlock the registry lock. */
+			mutex_unlock(&rcu_registry_lock);
+			if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS)
+				(void) poll(NULL, 0, RCU_SLEEP_DELAY_MS);
 			else
 				caa_cpu_relax();
+			/* Re-lock the registry lock before the next loop. */
+			mutex_lock(&rcu_registry_lock);
 		}
 	}
 }
@@ -218,6 +246,8 @@ void synchronize_rcu(void)
 
 	mutex_lock(&rcu_gp_lock);
 
+	mutex_lock(&rcu_registry_lock);
+
 	if (cds_list_empty(&registry))
 		goto out;
 
@@ -226,11 +256,10 @@ void synchronize_rcu(void)
 	/* Write new ptr before changing the qparity */
 	cmm_smp_mb();
 
-	/* Remove old registry elements */
-	rcu_gc_registry();
-
 	/*
 	 * Wait for readers to observe original parity or be quiescent.
+	 * wait_for_readers() can release and grab again rcu_registry_lock
+	 * interally.
 	 */
 	wait_for_readers(&registry, &cur_snap_readers, &qsreaders);
 
@@ -260,6 +289,8 @@ void synchronize_rcu(void)
 
 	/*
 	 * Wait for readers to observe new parity or be quiescent.
+	 * wait_for_readers() can release and grab again rcu_registry_lock
+	 * interally.
 	 */
 	wait_for_readers(&cur_snap_readers, NULL, &qsreaders);
 
@@ -274,6 +305,7 @@ void synchronize_rcu(void)
 	 */
 	cmm_smp_mb();
 out:
+	mutex_unlock(&rcu_registry_lock);
 	mutex_unlock(&rcu_gp_lock);
 	ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 	assert(!ret);
@@ -402,10 +434,14 @@ static
 void add_thread(void)
 {
 	struct rcu_reader *rcu_reader_reg;
+	int ret;
 
 	rcu_reader_reg = arena_alloc(&registry_arena);
 	if (!rcu_reader_reg)
 		abort();
+	ret = pthread_setspecific(urcu_bp_key, rcu_reader_reg);
+	if (ret)
+		abort();
 
 	/* Add to registry */
 	rcu_reader_reg->tid = pthread_self();
@@ -418,33 +454,39 @@ void add_thread(void)
 	URCU_TLS(rcu_reader) = rcu_reader_reg;
 }
 
-/* Called with signals off and mutex locked */
-static void rcu_gc_registry(void)
+/* Called with mutex locked */
+static
+void cleanup_thread(struct registry_chunk *chunk,
+		struct rcu_reader *rcu_reader_reg)
+{
+	rcu_reader_reg->ctr = 0;
+	cds_list_del(&rcu_reader_reg->node);
+	rcu_reader_reg->tid = 0;
+	rcu_reader_reg->alloc = 0;
+	chunk->used -= sizeof(struct rcu_reader);
+}
+
+static
+struct registry_chunk *find_chunk(struct rcu_reader *rcu_reader_reg)
 {
 	struct registry_chunk *chunk;
-	struct rcu_reader *rcu_reader_reg;
 
 	cds_list_for_each_entry(chunk, &registry_arena.chunk_list, node) {
-		for (rcu_reader_reg = (struct rcu_reader *) &chunk->data[0];
-				rcu_reader_reg < (struct rcu_reader *) &chunk->data[chunk->data_len];
-				rcu_reader_reg++) {
-			pthread_t tid;
-			int ret;
-
-			if (!rcu_reader_reg->alloc)
-				continue;
-			tid = rcu_reader_reg->tid;
-			ret = pthread_kill(tid, 0);
-			assert(ret != EINVAL);
-			if (ret == ESRCH) {
-				cds_list_del(&rcu_reader_reg->node);
-				rcu_reader_reg->ctr = 0;
-				rcu_reader_reg->alloc = 0;
-				chunk->used -= sizeof(struct rcu_reader);
-			}
-
-		}
+		if (rcu_reader_reg < (struct rcu_reader *) &chunk->data[0])
+			continue;
+		if (rcu_reader_reg >= (struct rcu_reader *) &chunk->data[chunk->data_len])
+			continue;
+		return chunk;
 	}
+	return NULL;
+}
+
+/* Called with signals off and mutex locked */
+static
+void remove_thread(struct rcu_reader *rcu_reader_reg)
+{
+	cleanup_thread(find_chunk(rcu_reader_reg), rcu_reader_reg);
+	URCU_TLS(rcu_reader) = NULL;
 }
 
 /* Disable signals, take mutex, add to registry */
@@ -454,38 +496,107 @@ void rcu_bp_register(void)
 	int ret;
 
 	ret = sigfillset(&newmask);
-	assert(!ret);
+	if (ret)
+		abort();
 	ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
-	assert(!ret);
+	if (ret)
+		abort();
 
 	/*
 	 * Check if a signal concurrently registered our thread since
-	 * the check in rcu_read_lock(). */
+	 * the check in rcu_read_lock().
+	 */
 	if (URCU_TLS(rcu_reader))
 		goto end;
 
-	mutex_lock(&rcu_gp_lock);
+	/*
+	 * Take care of early registration before urcu_bp constructor.
+	 */
+	rcu_bp_init();
+
+	mutex_lock(&rcu_registry_lock);
 	add_thread();
-	mutex_unlock(&rcu_gp_lock);
+	mutex_unlock(&rcu_registry_lock);
 end:
 	ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
-	assert(!ret);
+	if (ret)
+		abort();
 }
 
-void rcu_bp_exit(void)
+/* Disable signals, take mutex, remove from registry */
+static
+void rcu_bp_unregister(struct rcu_reader *rcu_reader_reg)
+{
+	sigset_t newmask, oldmask;
+	int ret;
+
+	ret = sigfillset(&newmask);
+	if (ret)
+		abort();
+	ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
+	if (ret)
+		abort();
+
+	mutex_lock(&rcu_registry_lock);
+	remove_thread(rcu_reader_reg);
+	mutex_unlock(&rcu_registry_lock);
+	ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
+	if (ret)
+		abort();
+	rcu_bp_exit();
+}
+
+/*
+ * Remove thread from the registry when it exits, and flag it as
+ * destroyed so garbage collection can take care of it.
+ */
+static
+void urcu_bp_thread_exit_notifier(void *rcu_key)
+{
+	rcu_bp_unregister(rcu_key);
+}
+
+static
+void rcu_bp_init(void)
 {
-	struct registry_chunk *chunk, *tmp;
+	mutex_lock(&init_lock);
+	if (!rcu_bp_refcount++) {
+		int ret;
 
-	cds_list_for_each_entry_safe(chunk, tmp,
-			&registry_arena.chunk_list, node) {
-		munmap(chunk, chunk->data_len + sizeof(struct registry_chunk));
+		ret = pthread_key_create(&urcu_bp_key,
+				urcu_bp_thread_exit_notifier);
+		if (ret)
+			abort();
+		initialized = 1;
+	}
+	mutex_unlock(&init_lock);
+}
+
+static
+void rcu_bp_exit(void)
+{
+	mutex_lock(&init_lock);
+	if (!--rcu_bp_refcount) {
+		struct registry_chunk *chunk, *tmp;
+		int ret;
+
+		cds_list_for_each_entry_safe(chunk, tmp,
+				&registry_arena.chunk_list, node) {
+			munmap(chunk, chunk->data_len
+					+ sizeof(struct registry_chunk));
+		}
+		ret = pthread_key_delete(urcu_bp_key);
+		if (ret)
+			abort();
 	}
+	mutex_unlock(&init_lock);
 }
 
 /*
- * Holding the rcu_gp_lock across fork will make sure we fork() don't race with
- * a concurrent thread executing with this same lock held. This ensures that the
- * registry is in a coherent state in the child.
+ * Holding the rcu_gp_lock and rcu_registry_lock across fork will make
+ * sure we fork() don't race with a concurrent thread executing with
+ * any of those locks held. This ensures that the registry and data
+ * protected by rcu_gp_lock are in a coherent state in the child.
  */
 void rcu_bp_before_fork(void)
 {
@@ -497,6 +608,7 @@ void rcu_bp_before_fork(void)
 	ret = pthread_sigmask(SIG_BLOCK, &newmask, &oldmask);
 	assert(!ret);
 	mutex_lock(&rcu_gp_lock);
+	mutex_lock(&rcu_registry_lock);
 	saved_fork_signal_mask = oldmask;
 }
 
@@ -506,18 +618,43 @@ void rcu_bp_after_fork_parent(void)
 	int ret;
 
 	oldmask = saved_fork_signal_mask;
+	mutex_unlock(&rcu_registry_lock);
 	mutex_unlock(&rcu_gp_lock);
 	ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 	assert(!ret);
 }
 
+/*
+ * Prune all entries from registry except our own thread. Fits the Linux
+ * fork behavior. Called with rcu_gp_lock and rcu_registry_lock held.
+ */
+static
+void urcu_bp_prune_registry(void)
+{
+	struct registry_chunk *chunk;
+	struct rcu_reader *rcu_reader_reg;
+
+	cds_list_for_each_entry(chunk, &registry_arena.chunk_list, node) {
+		for (rcu_reader_reg = (struct rcu_reader *) &chunk->data[0];
+				rcu_reader_reg < (struct rcu_reader *) &chunk->data[chunk->data_len];
+				rcu_reader_reg++) {
+			if (!rcu_reader_reg->alloc)
+				continue;
+			if (rcu_reader_reg->tid == pthread_self())
+				continue;
+			cleanup_thread(chunk, rcu_reader_reg);
+		}
+	}
+}
+
 void rcu_bp_after_fork_child(void)
 {
 	sigset_t oldmask;
 	int ret;
 
-	rcu_gc_registry();
+	urcu_bp_prune_registry();
 	oldmask = saved_fork_signal_mask;
+	mutex_unlock(&rcu_registry_lock);
 	mutex_unlock(&rcu_gp_lock);
 	ret = pthread_sigmask(SIG_SETMASK, &oldmask, NULL);
 	assert(!ret);