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      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:
     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 
     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 
     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 
     96 ExampleEmployer::ExampleEmployer() {
     97 }
     98 
     99 ExampleEmployer::~ExampleEmployer() {
    100 }
    101 
    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 
    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