[tsan] Add interceptor for xpc_connection_cancel to avoid false positives

[kubamracek]

Summary

TSan reports a false positive when using xpc_connection_cancel. We're missing a happens-before edge from xpc_connection_cancel to the event handler on the same connection.

lib/tsan/rtl/tsan_interceptors_mac.cc

xpc_handler_t new_handler = ^(xpc_object_t object) {
       SCOPED_INTERCEPTOR_RAW(xpc_connection_send_message_with_reply);
       Acquire(thr, pc, (uptr)connection);
     }
     handler(object);
   };
   REAL(xpc_connection_send_message_with_reply)
   (connection, message, replyq, new_handler);
 }
   
+TSAN_INTERCEPTOR(void, xpc_connection_cancel, xpc_connection_t connection) {
+  SCOPED_TSAN_INTERCEPTOR(xpc_connection_cancel, connection);
+  Release(thr, pc, (uptr)connection);
+  REAL(xpc_connection_cancel)(connection);
+}
+
 // On macOS, libc++ is always linked dynamically, so intercepting works the
 // usual way.
 #define STDCXX_INTERCEPTOR TSAN_INTERCEPTOR
 
 namespace {
 struct fake_shared_weak_count {
   volatile a64 shared_owners;
   volatile a64 shared_weak_owners;

test/tsan/Darwin/xpc-cancel.mm

+// RUN: %clang_tsan %s -o %t -framework Foundation
+// RUN: %run %t 2>&1 | FileCheck %s
+
+#import <Foundation/Foundation.h>
+#import <xpc/xpc.h>
+
+long global;
+
+int main(int argc, const char *argv[]) {
+  fprintf(stderr, "Hello world.\n");
+
+  dispatch_queue_t server_q = dispatch_queue_create("server.queue", DISPATCH_QUEUE_CONCURRENT);
+  xpc_connection_t server_conn = xpc_connection_create(NULL, server_q);
+
+  xpc_connection_set_event_handler(server_conn, ^(xpc_object_t client) {
+    if (client == XPC_ERROR_CONNECTION_INTERRUPTED || client == XPC_ERROR_CONNECTION_INVALID) {
+      global = 43;
+      
+      dispatch_async(dispatch_get_main_queue(), ^{
+        CFRunLoopStop(CFRunLoopGetCurrent());
+      });
+    }
+  });
+  xpc_connection_resume(server_conn);
+  
+  global = 42;
+  
+  xpc_connection_cancel(server_conn);
+  
+  CFRunLoopRun();
+
+  fprintf(stderr, "Done.\n");
+}
+
+// CHECK: Hello world.
+// CHECK-NOT: WARNING: ThreadSanitizer
+// CHECK: Done.