urcu-bp: perform thread registration on urcu_bp_register_thread

Some real-time use-cases (e.g. Xenomai) require to perform urcu-bp
thread registration early in the thread life-time before it starts
performing real-time tasks.

Currently, this can be achieved by issuing a urcu_bp_read_lock() and
urcu_bp_read_unlock() pair, or by using urcu_bp_read_ongoing(), while in
the initialization phrase.

However, it seems natural to expect that calling urcu_bp_register_thread()
would have the side effect to perform the lazy thread registration
immediately rather than being a no-op.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/README.md b/README.md
index 601703bdf6209af39c9e27e47a9d0c9d3e2d6b13..2d6dcaa2a4bfba1199c7dee5bcad5ec743acebf8 100644 (file)
--- a/README.md
+++ b/README.md
@@ -224,10 +224,11 @@ be overridden with `-DSIGRCU` by modifying `Makefile.build.inc`.
 
 The BP library flavor stands for "bulletproof". It is specifically
 designed to help tracing library to hook on applications without
 
 The BP library flavor stands for "bulletproof". It is specifically
 designed to help tracing library to hook on applications without

-requiring to modify these applications. `urcu_bp_init()`,
-`urcu_bp_register_thread()` and `urcu_bp_unregister_thread()` all become
-nops. The state is dealt with by the library internally at the expense
-of read-side and write-side performance.
+requiring to modify these applications. `urcu_bp_init()`, and
+`urcu_bp_unregister_thread()` all become nops, whereas calling
+`urcu_bp_register_thread()` becomes optional. The state is dealt with by
+the library internally at the expense of read-side and write-side
+performance.

 
 
 ### Initialization
 
 
 ### Initialization

diff --git a/include/urcu/urcu-bp.h b/include/urcu/urcu-bp.h
index d3d122d0f71df610a0276af0e3e5043a6adf4ee7..2ea17e6397391fae5e081118215ac717efbc0ae0 100644 (file)
--- a/include/urcu/urcu-bp.h
+++ b/include/urcu/urcu-bp.h
@@ -151,12 +151,14 @@ extern void urcu_bp_after_fork_parent(void);
 extern void urcu_bp_after_fork_child(void);
 
 /*
 extern void urcu_bp_after_fork_child(void);
 
 /*

- * In the bulletproof version, the following functions are no-ops.
+ * In the bulletproof version, thread registration is performed lazily,
+ * but it can be forced by issuing an explicit urcu_bp_register_thread().

  */
  */

-static inline void urcu_bp_register_thread(void)
-{
-}
+extern void urcu_bp_register_thread(void);

 
 

+/*
+ * In the bulletproof version, the following functions are no-ops.
+ */

 static inline void urcu_bp_unregister_thread(void)
 {
 }
 static inline void urcu_bp_unregister_thread(void)
 {
 }

diff --git a/src/urcu-bp.c b/src/urcu-bp.c
index 33f280799208c66f0337e25acfeaf8adce213aa1..05efd97eb67a2c05c99a09dfb5c6e29e888ff81e 100644 (file)
--- a/src/urcu-bp.c
+++ b/src/urcu-bp.c
@@ -566,6 +566,12 @@ end:
 }
 URCU_ATTR_ALIAS("urcu_bp_register") void rcu_bp_register();
 
 }
 URCU_ATTR_ALIAS("urcu_bp_register") void rcu_bp_register();
 

+void urcu_bp_register_thread(void)
+{
+       if (caa_unlikely(!URCU_TLS(urcu_bp_reader)))
+               urcu_bp_register(); /* If not yet registered. */
+}
+

 /* Disable signals, take mutex, remove from registry */
 static
 void urcu_bp_unregister(struct rcu_reader *rcu_reader_reg)
 /* Disable signals, take mutex, remove from registry */
 static
 void urcu_bp_unregister(struct rcu_reader *rcu_reader_reg)