From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Date: Fri, 3 Jun 2011 16:42:00 +0000 (-0400)
Subject: Provide pthread_atfork-friendly interfaces
X-Git-Tag: v0.6.0~45
X-Git-Url: http://git.lttng.org/?p=urcu.git;a=commitdiff_plain;h=81ad2e193e8072f8246212d7eaba72769306c2e4

Provide pthread_atfork-friendly interfaces

Provides call_rcu_before_fork() and call_rcu_after_fork_parent() to
go with the existing call_rcu_after_fork_child().

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---

diff --git a/README b/README
index f7f0dec..56e98d7 100644
--- a/README
+++ b/README
@@ -204,3 +204,7 @@ Interaction with fork()
 	liburcu-bp, which is designed to handle fork() by calling
 	rcu_bp_before_fork, rcu_bp_after_fork_parent and
 	rcu_bp_after_fork_child.
+
+	Applications that use call_rcu() are required to invoke
+	call_rcu_after_fork_child() from the child process after a
+	successful fork() system call that is not followed by exec().
diff --git a/urcu-call-rcu.c b/urcu-call-rcu.c
index bb56dbb..9cc56c5 100644
--- a/urcu-call-rcu.c
+++ b/urcu-call-rcu.c
@@ -565,14 +565,38 @@ void free_all_cpu_call_rcu_data(void)
 	}
 }
 
+/*
+ * Acquire the call_rcu_mutex in order to ensure that the child sees
+ * all of the call_rcu() data structures in a consistent state.
+ * Suitable for pthread_atfork() and friends.
+ */
+void call_rcu_before_fork(void)
+{
+	call_rcu_lock(&call_rcu_mutex);
+}
+
+/*
+ * Clean up call_rcu data structures in the parent of a successful fork()
+ * that is not followed by exec() in the child.  Suitable for
+ * pthread_atfork() and friends.
+ */
+void call_rcu_after_fork_parent(void)
+{
+	call_rcu_unlock(&call_rcu_mutex);
+}
+
 /*
  * Clean up call_rcu data structures in the child of a successful fork()
- * that is not followed by exec().
+ * that is not followed by exec().  Suitable for pthread_atfork() and
+ * friends.
  */
 void call_rcu_after_fork_child(void)
 {
 	struct call_rcu_data *crdp;
 
+	/* Release the mutex. */
+	call_rcu_unlock(&call_rcu_mutex);
+
 	/*
 	 * Allocate a new default call_rcu_data structure in order
 	 * to get a working call_rcu thread to go with it.