1 files changed, 50 insertions, 0 deletions
diff --git a/xpcom/threads/nsThreadSyncDispatch.h b/xpcom/threads/nsThreadSyncDispatch.h
new file mode 100644
index 000000000..ae5e85464
--- /dev/null
+++ b/xpcom/threads/nsThreadSyncDispatch.h
@@ -0,0 +1,50 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef nsThreadSyncDispatch_h_
+#define nsThreadSyncDispatch_h_
+
+#include "nsThreadUtils.h"
+#include "LeakRefPtr.h"
+#include "mozilla/DebugOnly.h"
+
+class nsThreadSyncDispatch : public mozilla::Runnable
+{
+public:
+  nsThreadSyncDispatch(nsIThread* aOrigin, already_AddRefed<nsIRunnable>&& aTask)
+    : mOrigin(aOrigin)
+    , mSyncTask(mozilla::Move(aTask))
+  {
+  }
+
+  bool IsPending()
+  {
+    return !!mSyncTask;
+  }
+
+private:
+  NS_IMETHOD Run() override
+  {
+    if (nsIRunnable* task = mSyncTask.get()) {
+      mozilla::DebugOnly<nsresult> result = task->Run();
+      MOZ_ASSERT(NS_SUCCEEDED(result),
+                 "task in sync dispatch should not fail");
+      // We must release the task here to ensure that when the original
+      // thread is unblocked, this task has been released.
+      mSyncTask.release();
+      // unblock the origin thread
+      mOrigin->Dispatch(this, NS_DISPATCH_NORMAL);
+    }
+    return NS_OK;
+  }
+
+  nsCOMPtr<nsIThread> mOrigin;
+  // The task is leaked by default when Run() is not called, because
+  // otherwise we may release it in an incorrect thread.
+  mozilla::LeakRefPtr<nsIRunnable> mSyncTask;
+};
+
+#endif // nsThreadSyncDispatch_h_