X-Git-Url: http://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu%2Ftls-compat.h;h=8ac1ea0615ddc2eb91ee51e9e15b89bd094d4c81;hp=9686ecaab139343547151e0f95697324c0442a55;hb=2af1c19e6a553878fcb2a5106f050d5ed7ac0f54;hpb=3db1417f5d2f17fdb62f328650c888ae3097c4c5

diff --git a/urcu/tls-compat.h b/urcu/tls-compat.h
index 9686eca..8ac1ea0 100644
--- a/urcu/tls-compat.h
+++ b/urcu/tls-compat.h
@@ -34,6 +34,36 @@ extern "C" {
 
 #ifdef CONFIG_RCU_TLS	/* Based on ax_tls.m4 */
 
+/*
+ * Hint: How to define/declare TLS variables of compound types
+ *       such as array or function pointers?
+ *
+ * Answer: Use typedef to assign a type_name to the compound type.
+ * Example: Define a TLS variable which is an int array with len=4:
+ *
+ * 	typedef int my_int_array_type[4];
+ * 	DEFINE_URCU_TLS(my_int_array_type, var_name);
+ *
+ * Another example:
+ * 	typedef void (*call_rcu_flavor)(struct rcu_head *, XXXX);
+ * 	DECLARE_URCU_TLS(call_rcu_flavor, p_call_rcu);
+ *
+ * NOTE: URCU_TLS() is NOT async-signal-safe, you can't use it
+ * inside any function which can be called from signal handler.
+ *
+ * But if pthread_getspecific() is async-signal-safe in your
+ * platform, you can make URCU_TLS() async-signal-safe via:
+ * ensuring the first call to URCU_TLS() of a given TLS variable of
+ * all threads is called earliest from a non-signal handler function.
+ *
+ * Example: In any thread, the first call of URCU_TLS(rcu_reader)
+ * is called from rcu_register_thread(), so we can ensure all later
+ * URCU_TLS(rcu_reader) in any thread is async-signal-safe.
+ *
+ * Moreover, URCU_TLS variables should not be touched from signal
+ * handlers setup with with sigaltstack(2).
+ */
+
 # define DECLARE_URCU_TLS(type, name)	\
 	CONFIG_RCU_TLS type name
 
@@ -44,6 +74,10 @@ extern "C" {
 
 #else /* #ifndef CONFIG_RCU_TLS */
 
+/*
+ * The *_1() macros ensure macro parameters are expanded.
+ */
+
 # include <pthread.h>
 
 struct urcu_tls {
@@ -52,14 +86,16 @@ struct urcu_tls {
 	int init_done;
 };
 
-# define DECLARE_URCU_TLS(type, name)				\
+# define DECLARE_URCU_TLS_1(type, name)				\
 	type *__tls_access_ ## name(void)
+# define DECLARE_URCU_TLS(type, name)				\
+	DECLARE_URCU_TLS_1(type, name)
 
 /*
  * Note: we don't free memory at process exit, since it will be dealt
  * with by the OS.
  */
-# define DEFINE_URCU_TLS(type, name)				\
+# define DEFINE_URCU_TLS_1(type, name)				\
 	type *__tls_access_ ## name(void)			\
 	{							\
 		static struct urcu_tls __tls_ ## name = {	\
@@ -88,7 +124,12 @@ struct urcu_tls {
 		return __tls_p;					\
 	}
 
-# define URCU_TLS(name)		(*__tls_access_ ## name())
+# define DEFINE_URCU_TLS(type, name)				\
+	DEFINE_URCU_TLS_1(type, name)
+
+# define URCU_TLS_1(name)	(*__tls_access_ ## name())
+
+# define URCU_TLS(name)		URCU_TLS_1(name)
 
 #endif	/* #else #ifndef CONFIG_RCU_TLS */