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// Copyright (c) 2011 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.
// Illustrates how to use worker threads that issue completion callbacks
#include "base/bind.h"
#include "base/logging.h"
#include "base/message_loop/message_loop.h"
#include "base/threading/worker_pool.h"
#include "net/base/completion_callback.h"
#include "net/base/test_completion_callback.h"
#include "testing/gtest/include/gtest/gtest.h"
#include "testing/platform_test.h"
typedef PlatformTest TestCompletionCallbackTest;
const int kMagicResult = 8888;
// ExampleEmployer is a toy version of HostResolver
// TODO: restore damage done in extracting example from real code
// (e.g. bring back real destructor, bring back comments)
class ExampleEmployer {
// Do some imaginary work on a worker thread;
// when done, worker posts callback on the original thread.
// Returns true on success
bool DoSomething(const net::CompletionCallback& callback);
class ExampleWorker;
friend class ExampleWorker;
scoped_refptr<ExampleWorker> request_;
// Helper class; this is how ExampleEmployer puts work on a different thread
class ExampleEmployer::ExampleWorker
: public base::RefCountedThreadSafe<ExampleWorker> {
ExampleWorker(ExampleEmployer* employer,
const net::CompletionCallback& callback)
: employer_(employer),
origin_loop_(base::MessageLoop::current()) {}
void DoWork();
void DoCallback();
friend class base::RefCountedThreadSafe<ExampleWorker>;
~ExampleWorker() {}
// Only used on the origin thread (where DoSomething was called).
ExampleEmployer* employer_;
net::CompletionCallback callback_;
// Used to post ourselves onto the origin thread.
base::Lock origin_loop_lock_;
base::MessageLoop* origin_loop_;
void ExampleEmployer::ExampleWorker::DoWork() {
// Running on the worker thread
// In a real worker thread, some work would be done here.
// Pretend it is, and send the completion callback.
// The origin loop could go away while we are trying to post to it, so we
// need to call its PostTask method inside a lock. See ~ExampleEmployer.
base::AutoLock locked(origin_loop_lock_);
if (origin_loop_)
base::Bind(&ExampleWorker::DoCallback, this));
void ExampleEmployer::ExampleWorker::DoCallback() {
// Running on the origin thread.
// Drop the employer_'s reference to us. Do this before running the
// callback since the callback might result in the employer being
// destroyed.
employer_->request_ = NULL;
ExampleEmployer::ExampleEmployer() {
ExampleEmployer::~ExampleEmployer() {
bool ExampleEmployer::DoSomething(const net::CompletionCallback& callback) {
DCHECK(!request_.get()) << "already in use";
request_ = new ExampleWorker(this, callback);
// Dispatch to worker thread...
if (!base::WorkerPool::PostTask(
base::Bind(&ExampleWorker::DoWork, request_.get()),
true)) {
request_ = NULL;
return false;
return true;
TEST_F(TestCompletionCallbackTest, Simple) {
ExampleEmployer boss;
net::TestCompletionCallback callback;
bool queued = boss.DoSomething(callback.callback());
EXPECT_EQ(queued, true);
int result = callback.WaitForResult();
EXPECT_EQ(result, kMagicResult);
// TODO: test deleting ExampleEmployer while work outstanding