X-Git-Url: https://git.liburcu.org/?a=blobdiff_plain;f=urcu%2Ftls-compat.h;h=601336b0db6599312bf4277a668f129c8e7c1645;hb=af67624df8d06ebaa5d72dd863a73d334611e900;hp=9686ecaab139343547151e0f95697324c0442a55;hpb=3db1417f5d2f17fdb62f328650c888ae3097c4c5;p=urcu.git

diff --git a/urcu/tls-compat.h b/urcu/tls-compat.h
index 9686eca..601336b 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 exmaple:
+ * 	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