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1 // Copyright (c) 2015 The Chromium Authors. All rights reserved. | 1 // Copyright (c) 2015 The Chromium Authors. All rights reserved. |
2 // Use of this source code is governed by a BSD-style license that can be | 2 // Use of this source code is governed by a BSD-style license that can be |
3 // found in the LICENSE file. | 3 // found in the LICENSE file. |
4 | 4 |
5 #ifndef MEDIA_BASE_BIND_TO_CURRENT_LOOP_H_ | 5 #ifndef MEDIA_BASE_BIND_TO_CURRENT_LOOP_H_ |
6 #define MEDIA_BASE_BIND_TO_CURRENT_LOOP_H_ | 6 #define MEDIA_BASE_BIND_TO_CURRENT_LOOP_H_ |
7 | 7 |
8 #include "base/bind.h" | 8 #include "base/bind.h" |
9 #include "base/location.h" | 9 #include "base/location.h" |
10 #include "base/memory/scoped_ptr.h" | |
10 #include "base/message_loop/message_loop_proxy.h" | 11 #include "base/message_loop/message_loop_proxy.h" |
11 #include "base/single_thread_task_runner.h" | 12 #include "base/single_thread_task_runner.h" |
13 #include "base/thread_task_runner_handle.h" | |
12 | 14 |
13 // This is a helper utility for base::Bind()ing callbacks to the current | 15 // This is a helper utility for base::Bind()ing callbacks to the current |
14 // MessageLoop. The typical use is when |a| (of class |A|) wants to hand a | 16 // MessageLoop. The typical use is when |a| (of class |A|) wants to hand a |
15 // callback such as base::Bind(&A::AMethod, a) to |b|, but needs to ensure that | 17 // callback such as base::Bind(&A::AMethod, a) to |b|, but needs to ensure that |
16 // when |b| executes the callback, it does so on |a|'s current MessageLoop. | 18 // when |b| executes the callback, it does so on |a|'s current MessageLoop. |
17 // | 19 // |
18 // Typical usage: request to be called back on the current thread: | 20 // Typical usage: request to be called back on the current thread: |
19 // other->StartAsyncProcessAndCallMeBack( | 21 // other->StartAsyncProcessAndCallMeBack( |
20 // media::BindToCurrentLoop(base::Bind(&MyClass::MyMethod, this))); | 22 // media::BindToCurrentLoop(base::Bind(&MyClass::MyMethod, this))); |
21 // | 23 // |
22 // Note that like base::Bind(), BindToCurrentLoop() can't bind non-constant | 24 // Note that like base::Bind(), BindToCurrentLoop() can't bind non-constant |
23 // references, and that *unlike* base::Bind(), BindToCurrentLoop() makes copies | 25 // references, and that *unlike* base::Bind(), BindToCurrentLoop() makes copies |
24 // of its arguments, and thus can't be used with arrays. | 26 // of its arguments, and thus can't be used with arrays. |
27 // | |
28 // The callback passed in to BindToCurrentLoop is guaranteed to be deleted on | |
29 // the thread from which BindToCurrentLoop was invoked. This allows objects that | |
30 // must be deleted on the originating thread to be bound into it. In particular, | |
31 // it can be useful to use WeakPtr<> in the callback so that the reply operation | |
32 // can be canceled. | |
25 | 33 |
26 namespace media { | 34 namespace media { |
27 | 35 |
36 namespace internal { | |
37 | |
28 // Mimic base::internal::CallbackForward, replacing p.Pass() with | 38 // Mimic base::internal::CallbackForward, replacing p.Pass() with |
29 // base::Passed(&p) to account for the extra layer of indirection. | 39 // base::Passed(&p) to account for the extra layer of indirection. |
30 namespace internal { | |
31 template <typename T> | 40 template <typename T> |
32 T& TrampolineForward(T& t) { return t; } | 41 T& TrampolineForward(T& t) { return t; } |
33 | 42 |
34 template <typename T, typename R> | 43 template <typename T, typename R> |
35 base::internal::PassedWrapper<scoped_ptr<T, R> > TrampolineForward( | 44 base::internal::PassedWrapper<scoped_ptr<T, R> > TrampolineForward( |
36 scoped_ptr<T, R>& p) { return base::Passed(&p); } | 45 scoped_ptr<T, R>& p) { return base::Passed(&p); } |
37 | 46 |
38 template <typename T> | 47 template <typename T> |
39 base::internal::PassedWrapper<ScopedVector<T> > TrampolineForward( | 48 base::internal::PassedWrapper<ScopedVector<T> > TrampolineForward( |
40 ScopedVector<T>& p) { return base::Passed(&p); } | 49 ScopedVector<T>& p) { return base::Passed(&p); } |
41 | 50 |
42 // First, tell the compiler TrampolineHelper is a struct template with one | 51 } // namespace internal |
43 // type parameter. Then define specializations where the type is a function | 52 |
44 // returning void and taking zero or more arguments. | 53 namespace { |
45 template <typename Sig> struct TrampolineHelper; | |
46 | 54 |
47 template <typename... Args> | 55 template <typename... Args> |
48 struct TrampolineHelper<void(Args...)> { | 56 class BindToCurrentLoopRelay { |
49 static void Run( | 57 public: |
50 const scoped_refptr<base::SingleThreadTaskRunner>& task_runner, | 58 BindToCurrentLoopRelay(const base::Callback<void(Args...)>& cb) |
51 const base::Callback<void(Args...)>& cb, | 59 // TODO(johnme): Caller of BindToCurrentLoop should pass in FROM_HERE. |
52 Args... args) { | 60 : from_here_(FROM_HERE), |
53 task_runner->PostTask(FROM_HERE, | 61 origin_loop_(base::ThreadTaskRunnerHandle::Get()), |
54 base::Bind(cb, TrampolineForward(args)...)); | 62 cb_ptr_(new base::Callback<void(Args...)>(cb)) {} |
63 | |
64 ~BindToCurrentLoopRelay() { | |
65 if (origin_loop_->BelongsToCurrentThread()) { | |
66 delete cb_ptr_; | |
67 } else if (!origin_loop_->DeleteSoon(from_here_, cb_ptr_)) { | |
danakj
2015/04/24 19:00:03
I think you want FROM_HERE here? Or why do you use
johnme
2015/04/27 18:32:33
Ok, I've changed both the |from_here_|s to FROM_HE
| |
68 // If DeleteSoon is not possible because the originating MessageLoop is no | |
69 // longer available, the Callback is leaked. Leaking is considered | |
70 // preferable to having thread-safety violations caused by invoking the | |
71 // Callback destructor on the wrong thread. | |
72 #if defined(UNIT_TEST) | |
73 // Only logged under unit testing because leaks at shutdown | |
74 // are acceptable under normal circumstances. | |
75 LOG(ERROR) << "DeleteSoon failed"; | |
danakj
2015/04/24 19:00:03
FATAL?
johnme
2015/04/27 18:32:33
I copied this from https://codereview.chromium.org
| |
76 #endif // UNIT_TEST | |
77 } | |
55 } | 78 } |
79 | |
80 void Run(Args... args) { | |
81 // Ignore return value; nothing we can do if PostTask fails. | |
82 origin_loop_->PostTask( | |
83 from_here_, base::Bind(*cb_ptr_, internal::TrampolineForward(args)...)); | |
danakj
2015/04/24 19:00:03
Would it be simpler to do this as follows?
templa
johnme
2015/04/27 18:32:33
If you delete the callback returned from BindToCur
| |
84 } | |
85 | |
86 private: | |
87 tracked_objects::Location from_here_; | |
88 scoped_refptr<base::SingleThreadTaskRunner> origin_loop_; | |
89 base::Callback<void(Args...)>* cb_ptr_; // Owned. | |
56 }; | 90 }; |
57 | 91 |
58 } // namespace internal | 92 } // namespace |
59 | 93 |
60 template<typename T> | 94 template<typename... Args> |
61 static base::Callback<T> BindToCurrentLoop( | 95 static base::Callback<void(Args...)> BindToCurrentLoop( |
62 const base::Callback<T>& cb) { | 96 const base::Callback<void(Args...)>& cb) { |
63 return base::Bind(&internal::TrampolineHelper<T>::Run, | 97 BindToCurrentLoopRelay<Args...>* relay = |
64 base::MessageLoopProxy::current(), cb); | 98 new BindToCurrentLoopRelay<Args...>(cb); |
99 return base::Bind(&BindToCurrentLoopRelay<Args...>::Run, | |
100 base::Owned(relay)); | |
65 } | 101 } |
66 | 102 |
67 } // namespace media | 103 } // namespace media |
68 | 104 |
69 #endif // MEDIA_BASE_BIND_TO_CURRENT_LOOP_H_ | 105 #endif // MEDIA_BASE_BIND_TO_CURRENT_LOOP_H_ |
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