X-Git-Url: http://git.liburcu.org/?a=blobdiff_plain;f=urcu.c;h=b71e162b3fca1e29f83e02b6cd405e68b154147e;hb=fc606a745f2825aff6c615e5d6703526e170906b;hp=efbb4b7890a71524fa8264877f3da63565291591;hpb=67c2d80b2b808fe7a6d6d0660ca81c919a81010b;p=urcu.git

diff --git a/urcu.c b/urcu.c
index efbb4b7..b71e162 100644
--- a/urcu.c
+++ b/urcu.c
@@ -36,6 +36,11 @@
 /* Do not #define _LGPL_SOURCE to ensure we can emit the wrapper symbols */
 #include "urcu.h"
 
+void __attribute__((constructor)) urcu_init(void);
+void __attribute__((destructor)) urcu_exit(void);
+
+int init_done;
+
 pthread_mutex_t urcu_mutex = PTHREAD_MUTEX_INITIALIZER;
 
 /*
@@ -249,12 +254,11 @@ void synchronize_rcu(void)
 	 */
 
 	/*
-	 * Current RCU formal verification model assumes sequential execution of
-	 * the write-side. Add core synchronization instructions. Can be removed
-	 * if the formal model is extended to prove that reordering is still
-	 * correct.
+	 * 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.
 	 */
-	sync_core();	/* Formal model assumes serialized execution */
+	smp_mb();
 
 	/*
 	 * Wait for previous parity to be empty of readers.
@@ -269,7 +273,12 @@ void synchronize_rcu(void)
 	 * Ensured by STORE_SHARED and LOAD_SHARED.
 	 */
 
-	sync_core();	/* Formal model assumes serialized execution */
+	/*
+	 * 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 */
 
@@ -281,7 +290,12 @@ void synchronize_rcu(void)
 	 * Ensured by STORE_SHARED and LOAD_SHARED.
 	 */
 
-	sync_core();	/* Formal model assumes serialized execution */
+	/*
+	 * 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.
@@ -388,6 +402,7 @@ 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();
 }
@@ -412,11 +427,23 @@ 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;
 	ret = sigaction(SIGURCU, &act, NULL);
 	if (ret) {
@@ -425,7 +452,7 @@ void __attribute__((constructor)) urcu_init(void)
 	}
 }
 
-void __attribute__((destructor)) urcu_exit(void)
+void urcu_exit(void)
 {
 	struct sigaction act;
 	int ret;