[tsan] Add support for GCD dispatch_suspend and dispatch_resume

[kubamracek]

Summary

GCD queues can be suspended and resumed with dispatch_suspend and dispatch_resume. Sometimes this is used as synchronization, e.g. in the following example, f1() is always fully executed before f2():

dispatch_suspend(q);
dispatch_async(q, ^{ f2(); });
f1();
dispatch_resume(q);

It seems to me that all we need to do is to add synchronization between the call to dispatch_resume and any subsequent executions of blocks in the queue that was resumed. We already have an Acquire(q) before the block executes, so this patch just adds the Release(q) in an interceptor of dispatch_resume.

lib/tsan/rtl/tsan_libdispatch_mac.cc

 
 TSAN_INTERCEPTOR(void, dispatch_io_close, dispatch_io_t channel,
                  dispatch_io_close_flags_t flags) {
   SCOPED_TSAN_INTERCEPTOR(dispatch_io_close, channel, flags);
   Release(thr, pc, (uptr)channel);  // Acquire() in dispatch_io_create[_*].
   return REAL(dispatch_io_close)(channel, flags);
 }
 
+// Resuming a suspended queue needs to synchronize with all subsequent
+// executions of blocks in that queue.
+TSAN_INTERCEPTOR(void, dispatch_resume, dispatch_object_t o) {
+  SCOPED_TSAN_INTERCEPTOR(dispatch_resume, o);
+  Release(thr, pc, (uptr)o);  // Synchronizes with the Acquire() on serial_sync
+                              // in dispatch_sync_pre_execute
+  return REAL(dispatch_resume)(o);
+}
+
 }  // namespace __tsan
 
 #endif  // SANITIZER_MAC

test/tsan/Darwin/gcd-suspend.mm

+// RUN: %clang_tsan %s -o %t -framework Foundation
+// RUN: %env_tsan_opts=ignore_interceptors_accesses=1 %run %t 2>&1 | FileCheck %s
+
+#import <Foundation/Foundation.h>
+
+long my_global = 0;
+
+int main(int argc, const char *argv[]) {
+  fprintf(stderr, "Hello world.\n");
+
+  dispatch_queue_t q1 = dispatch_queue_create("queue1", NULL);
+  dispatch_queue_t q2 = dispatch_queue_create("queue2", NULL);
+  dispatch_group_t g = dispatch_group_create();
+
+  dispatch_sync(q1, ^{
+    dispatch_suspend(q1);
+    dispatch_async(q2, ^{
+      my_global++;
+      dispatch_resume(q1);
+    });
+  });
+
+  dispatch_sync(q1, ^{
+    my_global++;
+  });
+
+  dispatch_sync(q1, ^{
+    dispatch_suspend(q1);
+    dispatch_group_enter(g);
+    dispatch_async(q1,^{ my_global++; });
+    dispatch_async(q1,^{ my_global++; });
+    dispatch_async(q1,^{ my_global++; dispatch_group_leave(g); });
+    my_global++;
+    dispatch_resume(q1);
+  });
+
+  dispatch_group_wait(g, DISPATCH_TIME_FOREVER);
+
+  fprintf(stderr, "Done.\n");
+  return 0;
+}
+
+// CHECK: Hello world.
+// CHECK-NOT: WARNING: ThreadSanitizer
+// CHECK: Done.