X-Git-Url: http://git.liburcu.org/?a=blobdiff_plain;f=README;h=197d8a5573764c14892f9f7ff5bd329b824bbf74;hb=2819ef641bb6e2f7aa60c28f3a8f5ad252aa7d00;hp=33038af3ab12c0cc96aacbedf3cf6e76ea2fd5f7;hpb=aac98a5504a989c227bb9290f2849abc9458811c;p=userspace-rcu.git

diff --git a/README b/README
index 33038af..197d8a5 100644
--- a/README
+++ b/README
@@ -47,6 +47,15 @@ supported, with the following exceptions:
   support. For ARM this was introduced with gcc 4.4:
     http://gcc.gnu.org/gcc-4.4/changes.html
 
+Clang version 3.0 (based on LLVM 3.0) is supported.
+
+Building on MacOS X (Darwin) requires a work-around for processor
+detection:
+  # 32-bit
+  ./configure --build=i686-apple-darwin11
+  # 64-bit
+  ./configure --build=x86_64-apple-darwin11
+
 For developers using the git tree:
 
 This source tree is based on the autotools suite from GNU to simplify
@@ -189,11 +198,12 @@ Being careful with signals
 	signal(7). The liburcu-mb and liburcu-qsbr versions of the Userspace RCU
 	library do not require any signal.
 
-	Read-side critical sections are allowed in a signal handler with
-	liburcu and liburcu-mb. Be careful, however, to disable these signals
+	Read-side critical sections are allowed in a signal handler,
+	except those setup with sigaltstack(2), with liburcu and
+	liburcu-mb. Be careful, however, to disable these signals
 	between thread creation and calls to rcu_register_thread(), because a
-	signal handler nesting on an unregistered thread would not be allowed to
-	call rcu_read_lock().
+	signal handler nesting on an unregistered thread would not be
+	allowed to call rcu_read_lock().
 
 	Read-side critical sections are _not_ allowed in a signal handler with
 	liburcu-qsbr, unless signals are disabled explicitly around each
@@ -258,4 +268,24 @@ Interaction with fork()
 	must invoke call_rcu_before_fork() before the fork() and
 	call_rcu_after_fork_parent() after the fork().  The child
 	process must invoke call_rcu_after_fork_child().
-	These three APIs are suitable for passing to pthread_atfork().
+	Even though these three APIs are suitable for passing to
+	pthread_atfork(), use of pthread_atfork() is *STRONGLY
+	DISCOURAGED* for programs calling the glibc memory allocator
+	(malloc(), calloc(), free(), ...) within call_rcu callbacks.
+	This is due to limitations in the way glibc memory allocator
+	handles calls to the memory allocator from concurrent threads
+	while the pthread_atfork() handlers are executing.
+	Combining e.g.:
+	* call to free() from callbacks executed within call_rcu worker
+	  threads,
+	* executing call_rcu atfork handlers within the glibc pthread
+	  atfork mechanism,
+	will sometimes trigger interesting process hangs. This usually
+	hangs on a memory allocator lock within glibc.
+
+Thread Local Storage (TLS)
+
+	Userspace RCU can fall back on pthread_getspecific() to emulate
+	TLS variables on systems where it is not available. This behavior
+	can be forced by specifying --disable-compiler-tls as configure
+	argument.