X-Git-Url: https://git.lttng.org/?p=urcu.git;a=blobdiff_plain;f=urcu.c;h=c210a1341ade8a189752417249bb47bca73a03aa;hp=8fd6195662d33a996467fe78a065cacf7d739b01;hb=538d7df5086144837beb7a9c1e2a94eb637b9904;hpb=af02d47e5d0712e5ccde6d8f1ee89f18de798cad

diff --git a/urcu.c b/urcu.c
index 8fd6195..c210a13 100644
--- a/urcu.c
+++ b/urcu.c
@@ -36,6 +36,17 @@
 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
 #include "urcu.h"
 
+#ifndef CONFIG_URCU_AVOID_SIGNALS
+void __attribute__((constructor)) urcu_init(void);
+void __attribute__((destructor)) urcu_exit(void);
+#else
+void urcu_init(void)
+{
+}
+#endif
+
+int init_done;
+
 pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
 
 /*
@@ -116,7 +127,7 @@ static void switch_next_urcu_qparity(void)
 	STORE_SHARED(urcu_gp_ctr, urcu_gp_ctr ^ RCU_GP_CTR_BIT);
 }
 
-#ifdef DEBUG_FULL_MB
+#ifdef CONFIG_URCU_AVOID_SIGNALS
 #ifdef HAS_INCOHERENT_CACHES
 static void force_mb_single_thread(struct reader_registry *index)
 {
@@ -128,7 +139,7 @@ static void force_mb_all_threads(void)
 {
 	smp_mb();
 }
-#else /* #ifdef DEBUG_FULL_MB */
+#else /* #ifdef CONFIG_URCU_AVOID_SIGNALS */
 #ifdef HAS_INCOHERENT_CACHES
 static void force_mb_single_thread(struct reader_registry *index)
 {
@@ -195,7 +206,7 @@ static void force_mb_all_threads(void)
 	}
 	smp_mb();	/* read ->need_mb before ending the barrier */
 }
-#endif /* #else #ifdef DEBUG_FULL_MB */
+#endif /* #else #ifdef CONFIG_URCU_AVOID_SIGNALS */
 
 void wait_for_quiescent_state(void)
 {
@@ -248,6 +259,13 @@ void synchronize_rcu(void)
 	 * 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 previous parity to be empty of readers.
 	 */
@@ -261,6 +279,13 @@ void synchronize_rcu(void)
 	 * 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();
+
 	switch_next_urcu_qparity();	/* 1 -> 0 */
 
 	/*
@@ -271,6 +296,13 @@ void synchronize_rcu(void)
 	 * 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 previous parity to be empty of readers.
 	 */
@@ -376,6 +408,7 @@ static void rcu_remove_reader(pthread_t id)
 void rcu_register_thread(void)
 {
 	internal_urcu_lock();
+	urcu_init();	/* In case gcc does not support constructor attribute */
 	rcu_add_reader(pthread_self());
 	internal_urcu_unlock();
 }
@@ -387,7 +420,7 @@ void rcu_unregister_thread(void)
 	internal_urcu_unlock();
 }
 
-#ifndef DEBUG_FULL_MB
+#ifndef CONFIG_URCU_AVOID_SIGNALS
 static void sigurcu_handler(int signo, siginfo_t *siginfo, void *context)
 {
 	/*
@@ -400,12 +433,26 @@ static void sigurcu_handler(int signo, siginfo_t *siginfo, void *context)
 	smp_mb();
 }
 
-void __attribute__((constructor)) urcu_init(void)
+/*
+ * urcu_init constructor. Called when the library is linked, but also when
+ * reader threads are calling rcu_register_thread().
+ * Should only be called by a single thread at a given time. This is ensured by
+ * holing the internal_urcu_lock() from rcu_register_thread() or by running at
+ * library load time, which should not be executed by multiple threads nor
+ * concurrently with rcu_register_thread() anyway.
+ */
+void urcu_init(void)
 {
 	struct sigaction act;
 	int ret;
 
+	if (init_done)
+		return;
+	init_done = 1;
+
 	act.sa_sigaction = sigurcu_handler;
+	act.sa_flags = SA_SIGINFO | SA_RESTART;
+	sigemptyset(&act.sa_mask);
 	ret = sigaction(SIGURCU, &act, NULL);
 	if (ret) {
 		perror("Error in sigaction");
@@ -413,7 +460,7 @@ void __attribute__((constructor)) urcu_init(void)
 	}
 }
 
-void __attribute__((destructor)) urcu_exit(void)
+void urcu_exit(void)
 {
 	struct sigaction act;
 	int ret;
@@ -426,4 +473,4 @@ void __attribute__((destructor)) urcu_exit(void)
 	assert(act.sa_sigaction == sigurcu_handler);
 	free(registry);
 }
-#endif /* #ifndef DEBUG_FULL_MB */
+#endif /* #ifndef CONFIG_URCU_AVOID_SIGNALS */