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
199
200
201
202
203
204
base / sequence_checker_impl.cc [blame]
// 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.
#include "base/sequence_checker_impl.h"
#include <algorithm>
#include <utility>
#include "base/check.h"
#include "base/compiler_specific.h"
#include "base/containers/contains.h"
#include "base/debug/stack_trace.h"
#include "base/ranges/algorithm.h"
#include "base/sequence_token.h"
#include "base/synchronization/lock_subtle.h"
#include "base/threading/platform_thread.h"
#include "base/threading/platform_thread_ref.h"
#include "base/threading/thread_checker.h"
#include "base/threading/thread_checker_impl.h"
#include "base/threading/thread_local_storage.h"
namespace base {
namespace {
bool g_log_stack = false;
}
// static
void SequenceCheckerImpl::EnableStackLogging() {
g_log_stack = true;
ThreadChecker::EnableStackLogging();
}
SequenceCheckerImpl::SequenceCheckerImpl() {
AutoLock auto_lock(lock_);
EnsureAssigned();
}
SequenceCheckerImpl::~SequenceCheckerImpl() = default;
SequenceCheckerImpl::SequenceCheckerImpl(SequenceCheckerImpl&& other) {
// Verify that `other` is called on the correct thread.
// Note: This binds `other` if not already bound.
CHECK(other.CalledOnValidSequence());
bound_at_ = std::move(other.bound_at_);
sequence_token_ = other.sequence_token_;
#if DCHECK_IS_ON()
locks_ = std::move(other.locks_);
#endif // DCHECK_IS_ON()
thread_ref_ = other.thread_ref_;
// `other.bound_at_` and `other.locks_` were moved so they're null.
DCHECK(!other.bound_at_);
#if DCHECK_IS_ON()
DCHECK(other.locks_.empty());
#endif // DCHECK_IS_ON()
other.sequence_token_ = internal::SequenceToken();
other.thread_ref_ = PlatformThreadRef();
}
SequenceCheckerImpl& SequenceCheckerImpl::operator=(
SequenceCheckerImpl&& other) {
// Verify that `other` is called on the correct thread.
// Note: This binds `other` if not already bound.
CHECK(other.CalledOnValidSequence());
TS_UNCHECKED_READ(bound_at_) = std::move(TS_UNCHECKED_READ(other.bound_at_));
TS_UNCHECKED_READ(sequence_token_) = TS_UNCHECKED_READ(other.sequence_token_);
#if DCHECK_IS_ON()
TS_UNCHECKED_READ(locks_) = std::move(TS_UNCHECKED_READ(other.locks_));
#endif // DCHECK_IS_ON()
TS_UNCHECKED_READ(thread_ref_) = TS_UNCHECKED_READ(other.thread_ref_);
// `other.bound_at_` and `other.locks_` were moved so they're null.
DCHECK(!TS_UNCHECKED_READ(other.bound_at_));
#if DCHECK_IS_ON()
DCHECK(TS_UNCHECKED_READ(other.locks_).empty());
#endif // DCHECK_IS_ON()
TS_UNCHECKED_READ(other.sequence_token_) = internal::SequenceToken();
TS_UNCHECKED_READ(other.thread_ref_) = PlatformThreadRef();
return *this;
}
bool SequenceCheckerImpl::CalledOnValidSequence(
std::unique_ptr<debug::StackTrace>* out_bound_at) const {
AutoLock auto_lock(lock_);
EnsureAssigned();
CHECK(!thread_ref_.is_null());
// Valid if current sequence is the bound sequence.
bool is_valid =
(sequence_token_ == internal::SequenceToken::GetForCurrentThread());
// Valid if holding a bound lock.
if (!is_valid) {
#if DCHECK_IS_ON()
for (uintptr_t lock : subtle::GetTrackedLocksHeldByCurrentThread()) {
if (Contains(locks_, lock)) {
is_valid = true;
break;
}
}
#endif // DCHECK_IS_ON()
}
// Valid if called from the bound thread after TLS destruction.
//
// TODO(pbos): This preserves existing behavior that `sequence_token_` is
// ignored after TLS shutdown. It should either be documented here why that is
// necessary (shouldn't this destroy on sequence?) or
// SequenceCheckerTest.FromThreadDestruction should be updated to reflect the
// expected behavior.
//
// crrev.com/682023 added this TLS-check to solve an edge case but that edge
// case was probably only a problem before TLS-destruction order was fixed in
// crrev.com/1119244. crrev.com/1117059 further improved TLS-destruction order
// of tokens by using `thread_local` and making it deterministic.
//
// See https://timsong-cpp.github.io/cppwp/n4140/basic.start.term: "If the
// completion of the constructor or dynamic initialization of an object with
// thread storage duration is sequenced before that of another, the completion
// of the destructor of the second is sequenced before the initiation of the
// destructor of the first."
if (!is_valid) {
is_valid = ThreadLocalStorage::HasBeenDestroyed() &&
thread_ref_ == PlatformThread::CurrentRef();
}
if (!is_valid) {
// Return false without modifying the state if this call is not guaranteed
// to be mutually exclusive with others that returned true. Not modifying
// the state allows future calls to return true if they are mutually
// exclusive with other calls that returned true.
// On failure, set the `out_bound_at` argument.
if (out_bound_at && bound_at_) {
*out_bound_at = std::make_unique<debug::StackTrace>(*bound_at_);
}
return false;
}
// Before returning true, modify the state so future calls only return true if
// they are guaranteed to be mutually exclusive with this one.
#if DCHECK_IS_ON()
// `locks_` must contain locks held at binding time and for all calls to
// `CalledOnValidSequence` that returned true afterwards.
std::erase_if(locks_, [](uintptr_t lock_ptr) {
return !Contains(subtle::GetTrackedLocksHeldByCurrentThread(), lock_ptr);
});
#endif // DCHECK_IS_ON()
// `sequence_token_` is reset if this returns true from a different sequence.
if (sequence_token_ != internal::SequenceToken::GetForCurrentThread()) {
sequence_token_ = internal::SequenceToken();
}
return true;
}
void SequenceCheckerImpl::DetachFromSequence() {
AutoLock auto_lock(lock_);
bound_at_.reset();
sequence_token_ = internal::SequenceToken();
#if DCHECK_IS_ON()
locks_.clear();
#endif // DCHECK_IS_ON()
thread_ref_ = PlatformThreadRef();
}
void SequenceCheckerImpl::EnsureAssigned() const {
// Use `thread_ref_` to determine if this checker is already bound, as it is
// always set when bound (unlike `sequence_token_` and `locks_` which may be
// cleared by `CalledOnValidSequence()` while this checker is still bound).
if (!thread_ref_.is_null()) {
return;
}
if (g_log_stack) {
bound_at_ = std::make_unique<debug::StackTrace>(size_t{10});
}
sequence_token_ = internal::SequenceToken::GetForCurrentThread();
#if DCHECK_IS_ON()
// Copy all held locks to `locks_`, except `&lock_` (this is an implementation
// detail of `SequenceCheckerImpl` and doesn't provide mutual exclusion
// guarantees to the caller).
DCHECK(locks_.empty());
ranges::remove_copy(subtle::GetTrackedLocksHeldByCurrentThread(),
std::back_inserter(locks_),
reinterpret_cast<uintptr_t>(&lock_));
#endif // DCHECK_IS_ON()
DCHECK(sequence_token_.IsValid());
thread_ref_ = PlatformThread::CurrentRef();
DCHECK(!thread_ref_.is_null());
}
} // namespace base