chromium/third_party/abseil-cpp/absl/base/internal/low_level_scheduling.h

// Copyright 2017 The Abseil Authors.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//      https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//
// Core interfaces and definitions used by by low-level interfaces such as
// SpinLock.

#ifndef ABSL_BASE_INTERNAL_LOW_LEVEL_SCHEDULING_H_
#define ABSL_BASE_INTERNAL_LOW_LEVEL_SCHEDULING_H_

#include "absl/base/internal/raw_logging.h"
#include "absl/base/internal/scheduling_mode.h"
#include "absl/base/macros.h"

// The following two declarations exist so SchedulingGuard may friend them with
// the appropriate language linkage.  These callbacks allow libc internals, such
// as function level statics, to schedule cooperatively when locking.
extern "C" bool __google_disable_rescheduling(void);
extern "C" void __google_enable_rescheduling(bool disable_result);

namespace absl {
ABSL_NAMESPACE_BEGIN
class CondVar;
class Mutex;

namespace synchronization_internal {
int MutexDelay(int32_t c, int mode);
}  // namespace synchronization_internal

namespace base_internal {

class SchedulingHelper;  // To allow use of SchedulingGuard.
class SpinLock;          // To allow use of SchedulingGuard.

// SchedulingGuard
// Provides guard semantics that may be used to disable cooperative rescheduling
// of the calling thread within specific program blocks.  This is used to
// protect resources (e.g. low-level SpinLocks or Domain code) that cooperative
// scheduling depends on.
//
// Domain implementations capable of rescheduling in reaction to involuntary
// kernel thread actions (e.g blocking due to a pagefault or syscall) must
// guarantee that an annotated thread is not allowed to (cooperatively)
// reschedule until the annotated region is complete.
//
// It is an error to attempt to use a cooperatively scheduled resource (e.g.
// Mutex) within a rescheduling-disabled region.
//
// All methods are async-signal safe.
class SchedulingGuard { … };

//------------------------------------------------------------------------------
// End of public interfaces.
//------------------------------------------------------------------------------

inline bool SchedulingGuard::ReschedulingIsAllowed() { … }

inline bool SchedulingGuard::DisableRescheduling() { … }

inline void SchedulingGuard::EnableRescheduling(bool /* disable_result */) { … }

inline SchedulingGuard::ScopedEnable::ScopedEnable()
    : … { … }
inline SchedulingGuard::ScopedEnable::~ScopedEnable() { … }

}  // namespace base_internal
ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_BASE_INTERNAL_LOW_LEVEL_SCHEDULING_H_