1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
|
// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef COMPONENTS_SYNC_BASE_WEAK_HANDLE_H_
#define COMPONENTS_SYNC_BASE_WEAK_HANDLE_H_
#include <cstddef>
#include <utility>
#include "base/check_op.h"
#include "base/compiler_specific.h"
#include "base/functional/bind.h"
#include "base/gtest_prod_util.h"
#include "base/location.h"
#include "base/memory/ref_counted.h"
#include "base/memory/weak_ptr.h"
#include "base/task/sequenced_task_runner.h"
// Weak handles provides a way to refer to weak pointers from another sequence.
// This is useful because it is not safe to reference a weak pointer from a
// sequence other than the sequence on which it will be invalidated.
//
// Weak handles can be passed across sequences, so for example, you can use them
// to do the "real" work on one thread and get notified on another thread:
//
// class FooIOWorker {
// public:
// FooIOWorker(const WeakHandle<Foo>& foo) : foo_(foo) {}
//
// void OnIOStart() {
// foo_.Call(FROM_HERE, &Foo::OnIOStart);
// }
//
// private:
// const WeakHandle<Foo> foo_;
// };
//
// class Foo {
// public:
// Foo() {
// SpawnFooIOWorkerOnIOThread(
// MakeWeakHandle(weak_ptr_factory_.GetWeakPtr()));
// }
//
// /* Will always be called on the correct sequence, and only if this
// object hasn't been destroyed. */
// void OnIOStart() { DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_); .. }
//
// private:
// SEQUENCE_CHECKER(sequence_checker_);
//
// base::WeakPtrFactory<Foo> weak_ptr_factory_{this};
// };
namespace base {
class Location;
} // namespace base
namespace syncer {
template <typename T>
class WeakHandle;
namespace internal {
// These classes are part of the WeakHandle implementation. DO NOT
// USE THESE CLASSES DIRECTLY YOURSELF.
// Base class for WeakHandleCore<T> to avoid template bloat. Handles
// the interaction with the owner thread and its message loop.
class WeakHandleCoreBase {
public:
// Assumes the current thread is the owner thread.
WeakHandleCoreBase();
WeakHandleCoreBase(const WeakHandleCoreBase&) = delete;
WeakHandleCoreBase& operator=(const WeakHandleCoreBase&) = delete;
// May be called on any thread.
bool IsOnOwnerThread() const;
protected:
// May be destroyed on any thread.
~WeakHandleCoreBase();
// May be called on any thread.
void PostToOwnerThread(const base::Location& from_here,
base::OnceClosure fn) const;
private:
// May be used on any thread.
const scoped_refptr<base::SequencedTaskRunner> owner_loop_task_runner_;
};
// WeakHandleCore<T> contains all the logic for WeakHandle<T>.
template <typename T>
class WeakHandleCore : public WeakHandleCoreBase,
public base::RefCountedThreadSafe<WeakHandleCore<T>> {
public:
// Must be called on `ptr`'s owner thread, which is assumed to be
// the current thread.
explicit WeakHandleCore(const base::WeakPtr<T>& ptr) : ptr_(ptr) {}
WeakHandleCore(const WeakHandleCore&) = delete;
WeakHandleCore& operator=(const WeakHandleCore&) = delete;
// Must be called on `ptr_`'s owner thread.
base::WeakPtr<T> Get() const {
DCHECK(IsOnOwnerThread());
return ptr_;
}
// Call(...) may be called on any thread, but all its arguments
// should be safe to be bound and copied across threads.
template <typename Method, typename... Args>
void Call(const base::Location& from_here,
Method method,
Args&&... args) const {
PostToOwnerThread(
from_here, base::BindOnce(method, ptr_, std::forward<Args>(args)...));
}
private:
friend class base::RefCountedThreadSafe<WeakHandleCore<T>>;
// May be destroyed on any thread.
~WeakHandleCore() = default;
// Must be dereferenced only on the owner thread. May be destroyed
// from any thread.
base::WeakPtr<T> ptr_;
};
} // namespace internal
// May be destroyed on any thread.
// Copying and assignment are welcome.
template <typename T>
class WeakHandle {
public:
// Creates an uninitialized WeakHandle.
WeakHandle() = default;
// Creates an initialized WeakHandle from `ptr`.
explicit WeakHandle(const base::WeakPtr<T>& ptr)
: core_(new internal::WeakHandleCore<T>(ptr)) {}
// Allow conversion from WeakHandle<U> to WeakHandle<T> if U is
// convertible to T, but we *must* be on `other`'s owner thread.
// Note that this doesn't override the regular copy constructor, so
// that one can be called on any thread.
template <typename U>
WeakHandle(const WeakHandle<U>& other) // NOLINT
: core_(other.IsInitialized()
? new internal::WeakHandleCore<T>(other.Get())
: nullptr) {}
// Returns true iff this WeakHandle is initialized. Note that being
// initialized isn't a guarantee that the underlying object is still
// alive.
bool IsInitialized() const { return core_.get() != nullptr; }
// Resets to an uninitialized WeakHandle.
void Reset() { core_ = nullptr; }
// Must be called only on the underlying object's owner thread.
base::WeakPtr<T> Get() const {
DCHECK(IsInitialized());
DCHECK(core_->IsOnOwnerThread());
return core_->Get();
}
// Call(...) may be called on any thread, but all its arguments
// should be safe to be bound and copied across threads.
template <typename Method, typename... Args>
void Call(const base::Location& from_here,
Method method,
Args&&... args) const {
DCHECK(IsInitialized());
core_->Call(from_here, method, std::forward<Args>(args)...);
}
private:
FRIEND_TEST_ALL_PREFIXES(WeakHandleTest, TypeConversionConstructor);
FRIEND_TEST_ALL_PREFIXES(WeakHandleTest, TypeConversionConstructorAssignment);
scoped_refptr<internal::WeakHandleCore<T>> core_;
};
// Makes a WeakHandle from a WeakPtr.
template <typename T>
WeakHandle<T> MakeWeakHandle(const base::WeakPtr<T>& ptr) {
return WeakHandle<T>(ptr);
}
} // namespace syncer
#endif // COMPONENTS_SYNC_BASE_WEAK_HANDLE_H_
|
