When linking libdispatch, register to create / destroy autorelease pools at the

correct time.  This fixes the intermittent problems when using libdispatch from
LanguageKit, among other things.

ANNOUNCE

@@ -21,6 +21,10 @@ Objective-C programs.  Highlights of this release include:
 - Significant improvements in property introspection and an exhaustive test
   suite.
 
+- Improved integration with libdispatch.  The runtime will correctly register
+  work queues with the garbage collector or create autorelease pools around
+  block invocations.
+
 - A new exception implementation providing better integration with foreign
   exceptions (e.g. C++ exceptions).  The new ABI is supported by clang 3.3 when
   compiling with -fobjc-runtime=gnustep-1.7 (or higher).  The old ABI is still

gc_none.c

@@ -21,6 +21,10 @@ static void *alloc(size_t size)
 	return calloc(size, 1);
 }
 
+void objc_registerThreadWithCollector(void) {}
+void objc_unregisterThreadWithCollector(void) {}
+void objc_assertRegisteredThreadWithCollector() {}
+
 PRIVATE struct gc_ops gc_ops_none = 
 {
 	.allocate_class = allocate_class,

loader.c

@@ -1,6 +1,8 @@
 #include <stdlib.h>
 #include <assert.h>
 #include "objc/runtime.h"
+#include "objc/objc-auto.h"
+#include "objc/objc-arc.h"
 #include "lock.h"
 #include "loader.h"
 #include "visibility.h"
@@ -35,6 +37,12 @@ static void log_memory_stats(void)
 /* Number of threads that are alive.  */
 int __objc_runtime_threads_alive = 1;			/* !T:MUTEX */
 
+// libdispatch hooks for registering threads
+__attribute__((weak)) void (*dispatch_begin_thread_4GC)(void);
+__attribute__((weak)) void (*dispatch_end_thread_4GC)(void);
+__attribute__((weak)) void *(*_dispatch_begin_NSAutoReleasePool)(void);
+__attribute__((weak)) void (*_dispatch_end_NSAutoReleasePool)(void *);
+
 void __objc_exec_class(struct objc_module_abi_8 *module)
 {
 	static BOOL first_run = YES;
@@ -73,6 +81,18 @@ void __objc_exec_class(struct objc_module_abi_8 *module)
 		{
 			atexit(log_memory_stats);
 		}
+		if (dispatch_begin_thread_4GC != 0) {
+			dispatch_begin_thread_4GC = objc_registerThreadWithCollector;
+		}
+		if (dispatch_end_thread_4GC != 0) {
+			dispatch_end_thread_4GC = objc_unregisterThreadWithCollector;
+		}
+		if (_dispatch_begin_NSAutoReleasePool != 0) {
+			_dispatch_begin_NSAutoReleasePool = objc_autoreleasePoolPush;
+		}
+		if (_dispatch_end_NSAutoReleasePool != 0) {
+			_dispatch_end_NSAutoReleasePool = objc_autoreleasePoolPop;
+		}
 	}
 
 	// The runtime mutex is held for the entire duration of a load.  It does