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// Copyright 2019 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.
#ifndef BASE_THREADING_SCOPED_THREAD_PRIORITY_H_
#define BASE_THREADING_SCOPED_THREAD_PRIORITY_H_
#include <atomic>
#include "base/base_export.h"
#include "base/compiler_specific.h"
#include "base/location.h"
#include "base/memory/raw_ptr.h"
#include "build/build_config.h"
#include "third_party/abseil-cpp/absl/types/optional.h"
namespace base {
class Location;
enum class ThreadType : int;
// INTERNAL_SCOPED_THREAD_PRIORITY_APPEND_LINE(name) produces an identifier by
// appending the current line number to |name|. This is used to avoid name
// collisions from variables defined inside a macro.
#define INTERNAL_SCOPED_THREAD_PRIORITY_CONCAT(a, b) a##b
// CONCAT1 provides extra level of indirection so that __LINE__ macro expands.
#define INTERNAL_SCOPED_THREAD_PRIORITY_CONCAT1(a, b) \
INTERNAL_SCOPED_THREAD_PRIORITY_CONCAT(a, b)
#define INTERNAL_SCOPED_THREAD_PRIORITY_APPEND_LINE(name) \
INTERNAL_SCOPED_THREAD_PRIORITY_CONCAT1(name, __LINE__)
// 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() \
static std::atomic_bool INTERNAL_SCOPED_THREAD_PRIORITY_APPEND_LINE( \
already_loaded){false}; \
base::internal::ScopedMayLoadLibraryAtBackgroundPriority \
INTERNAL_SCOPED_THREAD_PRIORITY_APPEND_LINE( \
scoped_may_load_library_at_background_priority)( \
FROM_HERE, \
&INTERNAL_SCOPED_THREAD_PRIORITY_APPEND_LINE(already_loaded));
// 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() \
base::internal::ScopedMayLoadLibraryAtBackgroundPriority \
INTERNAL_SCOPED_THREAD_PRIORITY_APPEND_LINE( \
scoped_may_load_library_at_background_priority)(FROM_HERE, nullptr);
// Boosts the current thread's priority to match the priority of threads of
// |target_thread_type| in this scope.
class BASE_EXPORT ScopedBoostPriority {
public:
explicit ScopedBoostPriority(ThreadType target_thread_type);
~ScopedBoostPriority();
ScopedBoostPriority(const ScopedBoostPriority&) = delete;
ScopedBoostPriority& operator=(const ScopedBoostPriority&) = delete;
private:
absl::optional<ThreadType> original_thread_type_;
};
namespace internal {
class BASE_EXPORT ScopedMayLoadLibraryAtBackgroundPriority {
public:
// Boosts thread priority to NORMAL within its scope if |already_loaded| is
// nullptr or set to false.
explicit ScopedMayLoadLibraryAtBackgroundPriority(
const Location& from_here,
std::atomic_bool* already_loaded);
ScopedMayLoadLibraryAtBackgroundPriority(
const ScopedMayLoadLibraryAtBackgroundPriority&) = delete;
ScopedMayLoadLibraryAtBackgroundPriority& operator=(
const ScopedMayLoadLibraryAtBackgroundPriority&) = delete;
~ScopedMayLoadLibraryAtBackgroundPriority();
private:
#if BUILDFLAG(IS_WIN)
// The original priority when invoking entering the scope().
absl::optional<ThreadType> original_thread_type_;
const raw_ptr<std::atomic_bool> already_loaded_;
#endif
};
} // namespace internal
} // namespace base
#endif // BASE_THREADING_SCOPED_THREAD_PRIORITY_H_