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// 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/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());
std::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
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