1 // Copyright (c) 2011 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 #include "base/threading/post_task_and_reply_impl.h"
6
7 #include "base/bind.h"
8 #include "base/location.h"
9 #include "base/single_thread_task_runner.h"
10 #include "base/thread_task_runner_handle.h"
11
12 namespace base {
13
14 namespace {
15
16 // This relay class remembers the MessageLoop that it was created on, and
17 // ensures that both the |task| and |reply| Closures are deleted on this same
18 // thread. Also, |task| is guaranteed to be deleted before |reply| is run or
19 // deleted.
20 //
21 // If this is not possible because the originating MessageLoop is no longer
22 // available, the the |task| and |reply| Closures are leaked. Leaking is
23 // considered preferable to having a thread-safetey violations caused by
24 // invoking the Closure destructor on the wrong thread.
25 class PostTaskAndReplyRelay {
26 public:
PostTaskAndReplyRelay(const tracked_objects::Location & from_here,const Closure & task,const Closure & reply)27 PostTaskAndReplyRelay(const tracked_objects::Location& from_here,
28 const Closure& task,
29 const Closure& reply)
30 : from_here_(from_here),
31 origin_task_runner_(ThreadTaskRunnerHandle::Get()) {
32 task_ = task;
33 reply_ = reply;
34 }
35
~PostTaskAndReplyRelay()36 ~PostTaskAndReplyRelay() {
37 DCHECK(origin_task_runner_->BelongsToCurrentThread());
38 task_.Reset();
39 reply_.Reset();
40 }
41
Run()42 void Run() {
43 task_.Run();
44 origin_task_runner_->PostTask(
45 from_here_, Bind(&PostTaskAndReplyRelay::RunReplyAndSelfDestruct,
46 base::Unretained(this)));
47 }
48
49 private:
RunReplyAndSelfDestruct()50 void RunReplyAndSelfDestruct() {
51 DCHECK(origin_task_runner_->BelongsToCurrentThread());
52
53 // Force |task_| to be released before |reply_| is to ensure that no one
54 // accidentally depends on |task_| keeping one of its arguments alive while
55 // |reply_| is executing.
56 task_.Reset();
57
58 reply_.Run();
59
60 // Cue mission impossible theme.
61 delete this;
62 }
63
64 tracked_objects::Location from_here_;
65 scoped_refptr<SingleThreadTaskRunner> origin_task_runner_;
66 Closure reply_;
67 Closure task_;
68 };
69
70 } // namespace
71
72 namespace internal {
73
PostTaskAndReply(const tracked_objects::Location & from_here,const Closure & task,const Closure & reply)74 bool PostTaskAndReplyImpl::PostTaskAndReply(
75 const tracked_objects::Location& from_here,
76 const Closure& task,
77 const Closure& reply) {
78 // TODO(tzik): Use DCHECK here once the crash is gone. http://crbug.com/541319
79 CHECK(!task.is_null()) << from_here.ToString();
80 CHECK(!reply.is_null()) << from_here.ToString();
81 PostTaskAndReplyRelay* relay =
82 new PostTaskAndReplyRelay(from_here, task, reply);
83 if (!PostTask(from_here, Bind(&PostTaskAndReplyRelay::Run,
84 Unretained(relay)))) {
85 delete relay;
86 return false;
87 }
88
89 return true;
90 }
91
92 } // namespace internal
93
94 } // namespace base
95