text: // 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_PROVIDER_BLOCKING_UI_THREAD_ASYNC_REQUEST_H_
  #define CHROME_BROWSER_ANDROID_PROVIDER_BLOCKING_UI_THREAD_ASYNC_REQUEST_H_
  
  #include "base/bind.h"
  #include "base/callback.h"
  #include "base/macros.h"
  #include "base/synchronization/waitable_event.h"
  #include "chrome/browser/android/provider/run_on_ui_thread_blocking.h"
  #include "content/public/browser/browser_thread.h"
  
  // Allows making async requests and blocking the current thread until the
  // response arrives. The request is performed in the UI thread.
  // Users of this class MUST call RequestCompleted when receiving the response.
  // Cannot be called directly from the UI thread.
  class BlockingUIThreadAsyncRequest {
   public:
    BlockingUIThreadAsyncRequest();
  
    // Runs an asynchronous request, blocking the invoking thread until a response
    // is received. Class users MUST call RequestCompleted when this happens.
    // Make sure that the response is also delivered to the UI thread.
    // The request argument can be defined using base::Bind.
    template <typename Signature>
    void RunAsyncRequestOnUIThreadBlocking(
        base::OnceCallback<Signature> request) {
      DCHECK(!content::BrowserThread::CurrentlyOn(content::BrowserThread::UI));
  
      // Make the request in the UI thread.
      request_completed_.Reset();
      RunOnUIThreadBlocking::Run(base::BindOnce(
          &BlockingUIThreadAsyncRequest::RunRequestOnUIThread<Signature>,
          std::move(request)));
  
      // Wait until the request callback invokes Finished.
      request_completed_.Wait();
    }
  
    // Notifies about a finished request.
    void RequestCompleted();
  
   private:
    template <typename Signature>
    static void RunRequestOnUIThread(base::OnceCallback<Signature> request) {
      std::move(request).Run();
    }
  
    base::WaitableEvent request_completed_;
  
    DISALLOW_COPY_AND_ASSIGN(BlockingUIThreadAsyncRequest);
  };
  
  #endif  // CHROME_BROWSER_ANDROID_PROVIDER_BLOCKING_UI_THREAD_ASYNC_REQUEST_H_
  