110 lines
4.1 KiB
C
110 lines
4.1 KiB
C
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// Copyright 2019 The Chromium Authors
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef BASE_THREADING_SCOPED_THREAD_PRIORITY_H_
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#define BASE_THREADING_SCOPED_THREAD_PRIORITY_H_
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#include <atomic>
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#include "base/base_export.h"
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#include "base/compiler_specific.h"
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#include "base/location.h"
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#include "base/memory/raw_ptr.h"
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#include "build/build_config.h"
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#include "third_party/abseil-cpp/absl/types/optional.h"
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namespace base {
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class Location;
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enum class ThreadType : int;
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// INTERNAL_SCOPED_THREAD_PRIORITY_APPEND_LINE(name) produces an identifier by
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// appending the current line number to |name|. This is used to avoid name
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// collisions from variables defined inside a macro.
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#define INTERNAL_SCOPED_THREAD_PRIORITY_CONCAT(a, b) a##b
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// CONCAT1 provides extra level of indirection so that __LINE__ macro expands.
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#define INTERNAL_SCOPED_THREAD_PRIORITY_CONCAT1(a, b) \
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INTERNAL_SCOPED_THREAD_PRIORITY_CONCAT(a, b)
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#define INTERNAL_SCOPED_THREAD_PRIORITY_APPEND_LINE(name) \
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INTERNAL_SCOPED_THREAD_PRIORITY_CONCAT1(name, __LINE__)
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// All code that may load a DLL on a background thread must be surrounded by a
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// scope that starts with this macro.
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//
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// Example:
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// Foo();
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// {
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// SCOPED_MAY_LOAD_LIBRARY_AT_BACKGROUND_PRIORITY();
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// LoadMyDll();
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// }
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// Bar();
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//
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// The macro raises the thread priority to NORMAL for the scope if no other
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// thread has completed the current scope already (multiple threads can racily
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// begin the initialization and will all be boosted for it). On Windows, loading
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// a DLL on a background thread can lead to a priority inversion on the loader
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// lock and cause huge janks.
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#define SCOPED_MAY_LOAD_LIBRARY_AT_BACKGROUND_PRIORITY() \
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static std::atomic_bool INTERNAL_SCOPED_THREAD_PRIORITY_APPEND_LINE( \
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already_loaded){false}; \
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base::internal::ScopedMayLoadLibraryAtBackgroundPriority \
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INTERNAL_SCOPED_THREAD_PRIORITY_APPEND_LINE( \
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scoped_may_load_library_at_background_priority)( \
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FROM_HERE, \
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&INTERNAL_SCOPED_THREAD_PRIORITY_APPEND_LINE(already_loaded));
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// Like SCOPED_MAY_LOAD_LIBRARY_AT_BACKGROUND_PRIORITY, but raises the thread
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// priority every time the scope is entered. Use this around code that may
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// conditionally load a DLL each time it is executed, or which repeatedly loads
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// and unloads DLLs.
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#define SCOPED_MAY_LOAD_LIBRARY_AT_BACKGROUND_PRIORITY_REPEATEDLY() \
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base::internal::ScopedMayLoadLibraryAtBackgroundPriority \
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INTERNAL_SCOPED_THREAD_PRIORITY_APPEND_LINE( \
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scoped_may_load_library_at_background_priority)(FROM_HERE, nullptr);
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// Boosts the current thread's priority to match the priority of threads of
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// |target_thread_type| in this scope.
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class BASE_EXPORT ScopedBoostPriority {
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public:
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explicit ScopedBoostPriority(ThreadType target_thread_type);
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~ScopedBoostPriority();
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ScopedBoostPriority(const ScopedBoostPriority&) = delete;
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ScopedBoostPriority& operator=(const ScopedBoostPriority&) = delete;
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private:
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absl::optional<ThreadType> original_thread_type_;
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};
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namespace internal {
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class BASE_EXPORT ScopedMayLoadLibraryAtBackgroundPriority {
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public:
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// Boosts thread priority to NORMAL within its scope if |already_loaded| is
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// nullptr or set to false.
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explicit ScopedMayLoadLibraryAtBackgroundPriority(
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const Location& from_here,
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std::atomic_bool* already_loaded);
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ScopedMayLoadLibraryAtBackgroundPriority(
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const ScopedMayLoadLibraryAtBackgroundPriority&) = delete;
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ScopedMayLoadLibraryAtBackgroundPriority& operator=(
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const ScopedMayLoadLibraryAtBackgroundPriority&) = delete;
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~ScopedMayLoadLibraryAtBackgroundPriority();
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private:
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#if BUILDFLAG(IS_WIN)
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// The original priority when invoking entering the scope().
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absl::optional<ThreadType> original_thread_type_;
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const raw_ptr<std::atomic_bool> already_loaded_;
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#endif
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};
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} // namespace internal
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} // namespace base
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#endif // BASE_THREADING_SCOPED_THREAD_PRIORITY_H_
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