revise based on review by das.

Author: dgrove-oss

private/private.h

@@ -166,7 +166,7 @@ void _dispatch_prohibit_transition_to_multithreaded(bool prohibit);
  * SPI for CoreFoundation/Foundation ONLY
  */
 
-#if (TARGET_OS_MAC || TARGET_OS_WIN32)
+#if TARGET_OS_MAC
 #define DISPATCH_COCOA_COMPAT 1
 #elif defined(__linux__)
 #define DISPATCH_COCOA_COMPAT 1
@@ -189,22 +189,17 @@ __OSX_AVAILABLE_STARTING(__MAC_10_6,__IPHONE_4_0)
 DISPATCH_EXPORT DISPATCH_CONST DISPATCH_WARN_RESULT DISPATCH_NOTHROW
 dispatch_runloop_handle_t
 _dispatch_get_main_queue_port_4CF(void);
+#endif
 
-__OSX_AVAILABLE_STARTING(__MAC_10_6,__IPHONE_4_0)
-DISPATCH_EXPORT DISPATCH_NOTHROW
-void
-_dispatch_main_queue_callback_4CF(mach_msg_header_t *_Null_unspecified msg);
-#else
-__OSX_AVAILABLE_STARTING(__MAC_10_6,__IPHONE_4_0)
+__OSX_AVAILABLE_STARTING(__MAC_10_12,__IPHONE_10_0)
 DISPATCH_EXPORT DISPATCH_NOTHROW
 dispatch_runloop_handle_t
 _dispatch_get_main_queue_handle_4CF(void);
 
 __OSX_AVAILABLE_STARTING(__MAC_10_6,__IPHONE_4_0)
 DISPATCH_EXPORT DISPATCH_NOTHROW
 void
-_dispatch_main_queue_callback_4CF(void);
-#endif
+_dispatch_main_queue_callback_4CF(void *_Null_unspecified msg);
 
 __OSX_AVAILABLE_STARTING(__MAC_10_9,__IPHONE_7_0)
 DISPATCH_EXPORT DISPATCH_MALLOC DISPATCH_RETURNS_RETAINED DISPATCH_WARN_RESULT

src/queue.c

@@ -4084,6 +4084,7 @@ _dispatch_runloop_queue_get_handle(dispatch_queue_t dq)
 #if TARGET_OS_MAC
 	return ((dispatch_runloop_handle_t)(uintptr_t)dq->do_ctxt);
 #elif defined(__linux__)
+	// decode: 0 is a valid fd, so offset by 1 to distinguish from NULL
 	return ((dispatch_runloop_handle_t)(uintptr_t)dq->do_ctxt) - 1;
 #else
 #error "runloop support not implemented on this platform"
@@ -4097,6 +4098,7 @@ _dispatch_runloop_queue_set_handle(dispatch_queue_t dq, dispatch_runloop_handle_
 #if TARGET_OS_MAC
 	dq->do_ctxt = (void *)(uintptr_t)handle;
 #elif defined(__linux__)
+	// encode: 0 is a valid fd, so offset by 1 to distinguish from NULL
 	dq->do_ctxt = (void *)(uintptr_t)(handle + 1);
 #else
 #error "runloop support not implemented on this platform"
@@ -4169,7 +4171,8 @@ _dispatch_runloop_queue_class_poke(dispatch_queue_t dq)
 	}
 
 #if TARGET_OS_MAC
-	kern_return_t kr = _dispatch_send_wakeup_runloop_thread(handle, 0);
+	mach_port_t mp = handle;
+	kern_return_t kr = _dispatch_send_wakeup_runloop_thread(mp, 0);
 	switch (kr) {
 	case MACH_SEND_TIMEOUT:
 	case MACH_SEND_TIMED_OUT:
@@ -5656,30 +5659,52 @@ _dispatch_runloop_queue_handle_init(void *ctxt)
 	_dispatch_fork_becomes_unsafe();
 
 #if TARGET_OS_MAC
+	mach_port_t mp;
 	kern_return_t kr;
-	kr = mach_port_allocate(mach_task_self(), MACH_PORT_RIGHT_RECEIVE, &handle);
+	kr = mach_port_allocate(mach_task_self(), MACH_PORT_RIGHT_RECEIVE, &mp);
 	DISPATCH_VERIFY_MIG(kr);
 	(void)dispatch_assume_zero(kr);
-	kr = mach_port_insert_right(mach_task_self(), handle, handle,
+	kr = mach_port_insert_right(mach_task_self(), mp, mp,
 			MACH_MSG_TYPE_MAKE_SEND);
 	DISPATCH_VERIFY_MIG(kr);
 	(void)dispatch_assume_zero(kr);
 	if (dq != &_dispatch_main_q) {
 		struct mach_port_limits limits = {
 			.mpl_qlimit = 1,
 		};
-		kr = mach_port_set_attributes(mach_task_self(), handle,
+		kr = mach_port_set_attributes(mach_task_self(), mp,
 				MACH_PORT_LIMITS_INFO, (mach_port_info_t)&limits,
 				sizeof(limits));
 		DISPATCH_VERIFY_MIG(kr);
 		(void)dispatch_assume_zero(kr);
 	}
+	handle = mp;
 #elif defined(__linux__)
-	handle = eventfd(0, EFD_CLOEXEC | EFD_NONBLOCK);
+	int fd = eventfd(0, EFD_CLOEXEC | EFD_NONBLOCK);
+	if (fd == -1) {
+		int err = errno;
+		switch (err) {
+		case EMFILE:
+			DISPATCH_CLIENT_CRASH(err, "eventfd() failure: "
+					"process is out of file descriptors");
+			break;
+		case ENFILE:
+			DISPATCH_CLIENT_CRASH(err, "eventfd() failure: "
+					"system is out of file descriptors");
+			break;
+		case ENOMEM:
+			DISPATCH_CLIENT_CRASH(err, "eventfd() failure: "
+					"kernel is out of memory");
+			break;
+		default:
+			DISPATCH_INTERNAL_CRASH(err, "eventfd() failure");
+			break;
+		}
+	}
+	handle = fd;
 #else
 #error "runloop support not implemented on this platform"
 #endif	
-	(void)dispatch_assume(_dispatch_runloop_handle_is_valid(handle));
 	_dispatch_runloop_queue_set_handle(dq, handle);
 
 	_dispatch_program_is_probably_callback_driven = true;
@@ -5694,7 +5719,8 @@ _dispatch_runloop_queue_handle_dispose(dispatch_queue_t dq)
 	}
 	dq->do_ctxt = NULL;
 #if TARGET_OS_MAC
-	kern_return_t kr = mach_port_deallocate(mach_task_self(), hand);
+	mach_port_t mp = handle;
+	kern_return_t kr = mach_port_deallocate(mach_task_self(), mp);
 	DISPATCH_VERIFY_MIG(kr);
 	(void)dispatch_assume_zero(kr);
 	kr = mach_port_mod_refs(mach_task_self(), mp, MACH_PORT_RIGHT_RECEIVE, -1);
@@ -5712,18 +5738,22 @@ _dispatch_runloop_queue_handle_dispose(dispatch_queue_t dq)
 #pragma mark dispatch_main_queue
 
 dispatch_runloop_handle_t
-#if TARGET_OS_MAC
-_dispatch_get_main_queue_port_4CF(void)
-#else
 _dispatch_get_main_queue_handle_4CF(void)
-#endif
 {
 	dispatch_queue_t dq = &_dispatch_main_q;
 	dispatch_once_f(&_dispatch_main_q_handle_pred, dq,
 			_dispatch_runloop_queue_handle_init);
 	return _dispatch_runloop_queue_get_handle(dq);
 }
 
+#if TARGET_OS_MAC
+dispatch_runloop_handle_t
+_dispatch_get_main_queue_port_4CF(void)
+{
+	return _dispatch_get_main_queue_handle_4CF();
+}
+#endif
+
 static bool main_q_is_draining;
 
 // 6618342 Contact the team that owns the Instrument DTrace probe before
@@ -5736,11 +5766,7 @@ _dispatch_queue_set_mainq_drain_state(bool arg)
 }
 
 void
-#if TARGET_OS_MAC
-_dispatch_main_queue_callback_4CF(mach_msg_header_t *msg DISPATCH_UNUSED)
-#else
-_dispatch_main_queue_callback_4CF(void)
-#endif
+_dispatch_main_queue_callback_4CF(void *ignored DISPATCH_UNUSED)
 {
 	if (main_q_is_draining) {
 		return;