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// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include "base/memory/ref_counted.h"
#include <limits>
#include <type_traits>
#include "base/threading/thread_collision_warner.h"
namespace base {
namespace {
#if DCHECK_IS_ON()
std::atomic_int g_cross_thread_ref_count_access_allow_count(0);
#endif
} // namespace
namespace subtle {
bool RefCountedThreadSafeBase::HasOneRef() const {
return ref_count_.IsOne();
}
bool RefCountedThreadSafeBase::HasAtLeastOneRef() const {
return !ref_count_.IsZero();
}
#if DCHECK_IS_ON()
RefCountedThreadSafeBase::~RefCountedThreadSafeBase() {
DCHECK(in_dtor_) << "RefCountedThreadSafe object deleted without "
"calling Release()";
}
#endif
// For security and correctness, we check the arithmetic on ref counts.
//
// In an attempt to avoid binary bloat (from inlining the `CHECK`), we define
// these functions out-of-line. However, compilers are wily. Further testing may
// show that `NOINLINE` helps or hurts.
//
#if defined(ARCH_CPU_64_BITS)
void RefCountedBase::AddRefImpl() const {
// An attacker could induce use-after-free bugs, and potentially exploit them,
// by creating so many references to a ref-counted object that the reference
// count overflows. On 32-bit architectures, there is not enough address space
// to succeed. But on 64-bit architectures, it might indeed be possible.
// Therefore, we can elide the check for arithmetic overflow on 32-bit, but we
// must check on 64-bit.
//
// Make sure the addition didn't wrap back around to 0. This form of check
// works because we assert that `ref_count_` is an unsigned integer type.
CHECK(++ref_count_ != 0);
}
void RefCountedBase::ReleaseImpl() const {
// Make sure the subtraction didn't wrap back around from 0 to the max value.
// That could cause memory leaks, and may induce application-semantic
// correctness or safety bugs. (E.g. what if we really needed that object to
// be destroyed at the right time?)
//
// Note that unlike with overflow, underflow could also happen on 32-bit
// architectures. Arguably, we should do this check on32-bit machines too.
CHECK(--ref_count_ != std::numeric_limits<decltype(ref_count_)>::max());
}
#endif
#if !defined(ARCH_CPU_X86_FAMILY)
bool RefCountedThreadSafeBase::Release() const {
return ReleaseImpl();
}
void RefCountedThreadSafeBase::AddRef() const {
AddRefImpl();
}
void RefCountedThreadSafeBase::AddRefWithCheck() const {
AddRefWithCheckImpl();
}
#endif
#if DCHECK_IS_ON()
bool RefCountedBase::CalledOnValidSequence() const {
#if defined(MOZ_SANDBOX)
return true;
#else
return sequence_checker_.CalledOnValidSequence() ||
g_cross_thread_ref_count_access_allow_count.load() != 0;
#endif
}
#endif
} // namespace subtle
#if DCHECK_IS_ON()
ScopedAllowCrossThreadRefCountAccess::ScopedAllowCrossThreadRefCountAccess() {
++g_cross_thread_ref_count_access_allow_count;
}
ScopedAllowCrossThreadRefCountAccess::~ScopedAllowCrossThreadRefCountAccess() {
--g_cross_thread_ref_count_access_allow_count;
}
#endif
} // namespace base