1// Copyright (c) 2010 The Chromium Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5// Illustrates how to use worker threads that issue completion callbacks
6
7#include "base/logging.h"
8#include "base/message_loop.h"
9#include "base/task.h"
10#include "base/threading/worker_pool.h"
11#include "net/base/completion_callback.h"
12#include "net/base/test_completion_callback.h"
13#include "testing/gtest/include/gtest/gtest.h"
14#include "testing/platform_test.h"
15
16typedef PlatformTest TestCompletionCallbackTest;
17
18using net::CompletionCallback;
19
20const int kMagicResult = 8888;
21
22// ExampleEmployer is a toy version of HostResolver
23// TODO: restore damage done in extracting example from real code
24// (e.g. bring back real destructor, bring back comments)
25class ExampleEmployer {
26 public:
27  ExampleEmployer();
28  ~ExampleEmployer();
29
30  // Do some imaginary work on a worker thread;
31  // when done, worker posts callback on the original thread.
32  // Returns true on success
33  bool DoSomething(CompletionCallback* callback);
34
35 private:
36  class ExampleWorker;
37  friend class ExampleWorker;
38  scoped_refptr<ExampleWorker> request_;
39  DISALLOW_COPY_AND_ASSIGN(ExampleEmployer);
40};
41
42// Helper class; this is how ExampleEmployer puts work on a different thread
43class ExampleEmployer::ExampleWorker
44    : public base::RefCountedThreadSafe<ExampleWorker> {
45 public:
46  ExampleWorker(ExampleEmployer* employer, CompletionCallback* callback)
47      : employer_(employer), callback_(callback),
48        origin_loop_(MessageLoop::current()) {
49  }
50  void DoWork();
51  void DoCallback();
52 private:
53  friend class base::RefCountedThreadSafe<ExampleWorker>;
54
55  ~ExampleWorker() {}
56
57  // Only used on the origin thread (where DoSomething was called).
58  ExampleEmployer* employer_;
59  CompletionCallback* callback_;
60  // Used to post ourselves onto the origin thread.
61  base::Lock origin_loop_lock_;
62  MessageLoop* origin_loop_;
63};
64
65void ExampleEmployer::ExampleWorker::DoWork() {
66  // Running on the worker thread
67  // In a real worker thread, some work would be done here.
68  // Pretend it is, and send the completion callback.
69  Task* reply = NewRunnableMethod(this, &ExampleWorker::DoCallback);
70
71  // The origin loop could go away while we are trying to post to it, so we
72  // need to call its PostTask method inside a lock.  See ~ExampleEmployer.
73  {
74    base::AutoLock locked(origin_loop_lock_);
75    if (origin_loop_) {
76      origin_loop_->PostTask(FROM_HERE, reply);
77      reply = NULL;
78    }
79  }
80
81  // Does nothing if it got posted.
82  delete reply;
83}
84
85void ExampleEmployer::ExampleWorker::DoCallback() {
86  // Running on the origin thread.
87
88  // Drop the employer_'s reference to us.  Do this before running the
89  // callback since the callback might result in the employer being
90  // destroyed.
91  employer_->request_ = NULL;
92
93  callback_->Run(kMagicResult);
94}
95
96ExampleEmployer::ExampleEmployer() {
97}
98
99ExampleEmployer::~ExampleEmployer() {
100}
101
102bool ExampleEmployer::DoSomething(CompletionCallback* callback) {
103  DCHECK(!request_) << "already in use";
104
105  request_ = new ExampleWorker(this, callback);
106
107  // Dispatch to worker thread...
108  if (!base::WorkerPool::PostTask(FROM_HERE,
109          NewRunnableMethod(request_.get(), &ExampleWorker::DoWork), true)) {
110    NOTREACHED();
111    request_ = NULL;
112    return false;
113  }
114
115  return true;
116}
117
118TEST_F(TestCompletionCallbackTest, Simple) {
119  ExampleEmployer boss;
120  TestCompletionCallback callback;
121  bool queued = boss.DoSomething(&callback);
122  EXPECT_EQ(queued, true);
123  int result = callback.WaitForResult();
124  EXPECT_EQ(result, kMagicResult);
125}
126
127// TODO: test deleting ExampleEmployer while work outstanding
128