[Android] Upstream ChromeBrowserProvider, the Android port ContentProvider implementation.

chrome/browser/android/run_on_ui_thread_blocking.h

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_ANDROID_RUN_ON_UI_THREAD_BLOCKING_H_
+#define CHROME_BROWSER_ANDROID_RUN_ON_UI_THREAD_BLOCKING_H_
+
+#include "base/bind.h"
+#include "base/callback.h"
+#include "base/synchronization/waitable_event.h"
+#include "content/public/browser/browser_thread.h"
+
+// Runs code synchronously on the UI thread. Should never be called directly
+// from the UI thread.
+class RunOnUIThreadBlocking {

[Yaron, 2012/09/10 19:30:04]

Hmm. This seems like a generally dangerous class, right? And it's only used by
browser provider because the user isn't actually waiting for it (well the chrome
browser isn't). can you at least comment it as such? Ideally it could be in a
sub-folder or something to indicate that it's not intended for re-use 

[Leandro Gracia Gil, 2012/09/10 22:21:48]

Moving the provider code to a subfolder and adding a comment here.

On 2012/09/10 19:30:04, Yaron wrote:

+ public:
+  // Runs the provided runnable in the UI thread synchronously.
+  // The runnable argument can be defined using base::Bind.
+  template <typename Signature>
+  static void Run(base::Callback<Signature> runnable) {
+    DCHECK(!content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
+    base::WaitableEvent finished(false, false);
+    content::BrowserThread::PostTask(content::BrowserThread::UI, FROM_HERE,
+          base::Bind(&RunOnUIThreadBlocking::RunOnUIThread<Signature>,
+                     runnable, &finished));
+    finished.Wait();
+  }
+
+ private:
+  template <typename Signature>
+  static void RunOnUIThread(base::Callback<Signature> runnable,
+                            base::WaitableEvent* finished) {
+    DCHECK(content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
+    runnable.Run();
+    finished->Signal();
+  }
+};
+
+#endif  // CHROME_BROWSER_ANDROID_RUN_ON_UI_THREAD_BLOCKING_H_