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
16 typedef PlatformTest TestCompletionCallbackTest;
17
18 using net::CompletionCallback;
19
20 const 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)
25 class 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
43 class ExampleEmployer::ExampleWorker
44 : public base::RefCountedThreadSafe<ExampleWorker> {
45 public:
ExampleWorker(ExampleEmployer * employer,CompletionCallback * callback)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
~ExampleWorker()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
DoWork()65 void 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
DoCallback()85 void 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
ExampleEmployer()96 ExampleEmployer::ExampleEmployer() {
97 }
98
~ExampleEmployer()99 ExampleEmployer::~ExampleEmployer() {
100 }
101
DoSomething(CompletionCallback * callback)102 bool 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
TEST_F(TestCompletionCallbackTest,Simple)118 TEST_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