chromium/base/threading/scoped_thread_priority.h

// Copyright 2019 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef BASE_THREADING_SCOPED_THREAD_PRIORITY_H_
#define BASE_THREADING_SCOPED_THREAD_PRIORITY_H_

#include <atomic>
#include <optional>

#include "base/base_export.h"
#include "base/compiler_specific.h"
#include "base/location.h"
#include "base/macros/uniquify.h"
#include "base/memory/raw_ptr.h"
#include "build/build_config.h"

namespace base {

class Location;
enum class ThreadType : int;

// All code that may load a DLL on a background thread must be surrounded by a
// scope that starts with this macro.
//
// Example:
//   Foo();
//   {
//     SCOPED_MAY_LOAD_LIBRARY_AT_BACKGROUND_PRIORITY();
//     LoadMyDll();
//   }
//   Bar();
//
// The macro raises the thread priority to NORMAL for the scope if no other
// thread has completed the current scope already (multiple threads can racily
// begin the initialization and will all be boosted for it). On Windows, loading
// a DLL on a background thread can lead to a priority inversion on the loader
// lock and cause huge janks.
#define SCOPED_MAY_LOAD_LIBRARY_AT_BACKGROUND_PRIORITY() …

// Like SCOPED_MAY_LOAD_LIBRARY_AT_BACKGROUND_PRIORITY, but raises the thread
// priority every time the scope is entered. Use this around code that may
// conditionally load a DLL each time it is executed, or which repeatedly loads
// and unloads DLLs.
#define SCOPED_MAY_LOAD_LIBRARY_AT_BACKGROUND_PRIORITY_REPEATEDLY() …

// Boosts the current thread's priority to match the priority of threads of
// |target_thread_type| in this scope.
class BASE_EXPORT ScopedBoostPriority { … };

namespace internal {

class BASE_EXPORT ScopedMayLoadLibraryAtBackgroundPriority { … };

}  // namespace internal

}  // namespace base

#endif  // BASE_THREADING_SCOPED_THREAD_PRIORITY_H_