[vm] Make FFI code protection test wait for helper to terminate before continuing.

Addresses #37779

Change-Id: I3ee7ec890be9c859737e8676a00047e46643e050
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/112258
Commit-Queue: Samir Jindel <sjindel@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>

Author: sjindel-google

runtime/bin/ffi_test/ffi_test_functions.cc

@@ -560,23 +560,28 @@ DART_EXPORT void* UnprotectCodeOtherThread(void* isolate,
   return nullptr;
 }
 
-DART_EXPORT int UnprotectCode() {
+DART_EXPORT void* UnprotectCode() {
   std::mutex mutex;
   std::condition_variable cvar;
   std::unique_lock<std::mutex> lock(mutex);  // locks the mutex
-  std::thread helper(UnprotectCodeOtherThread, Dart_CurrentIsolate(), &cvar,
-                     &mutex);
+  std::thread* helper = new std::thread(UnprotectCodeOtherThread,
+                                        Dart_CurrentIsolate(), &cvar, &mutex);
 
-  helper.detach();
   cvar.wait(lock);
 
-  return 0;
+  return helper;
+}
+
+DART_EXPORT void WaitForHelper(void* helper) {
+  std::thread* thread = reinterpret_cast<std::thread*>(helper);
+  thread->join();
 }
 #else
 // Our version of VSC++ doesn't support std::thread yet.
-DART_EXPORT int UnprotectCode() {
-  return 0;
+DART_EXPORT void* UnprotectCode() {
+  return nullptr;
 }
+DART_EXPORT void WaitForHelper(void* helper) {}
 #endif
 
 ////////////////////////////////////////////////////////////////////////////////

tests/ffi/function_gc_test.dart

@@ -110,10 +110,13 @@ void testRegress37069() {
   regress37069(1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11);
 }
 
-final unprotectCode = ffiTestFunctions
-    .lookupFunction<NativeNullaryOp32, NullaryOp>("UnprotectCode");
+final unprotectCode = ffiTestFunctions.lookupFunction<
+    ffi.Pointer<ffi.Void> Function(),
+    ffi.Pointer<ffi.Void> Function()>("UnprotectCode");
+final waitForHelper = ffiTestFunctions.lookupFunction<
+    ffi.Void Function(ffi.Pointer<ffi.Void>),
+    void Function(ffi.Pointer<ffi.Void>)>("UnprotectCode");
 
 void testWriteProtection() {
-  int result = unprotectCode();
-  Expect.equals(result, 0);
+  waitForHelper(unprotectCode());
 }