85 lines
3.3 KiB
C++
85 lines
3.3 KiB
C++
// Copyright 2019 The Chromium Authors. All rights reserved.
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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 "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/macros.h"
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#include "base/optional.h"
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#include "build/build_config.h"
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namespace base {
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class Location;
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enum class ThreadPriority : 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 when first
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// encountered. On Windows, loading a DLL on a background thread can lead to a
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// priority inversion on the loader lock and cause huge janks.
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#define SCOPED_MAY_LOAD_LIBRARY_AT_BACKGROUND_PRIORITY() \
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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); \
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{ \
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/* Thread-safe static local variable initialization ensures that */ \
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/* OnScopeFirstEntered() is only invoked the first time that this is */ \
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/* encountered. */ \
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static bool INTERNAL_SCOPED_THREAD_PRIORITY_APPEND_LINE(invoke_once) = \
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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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.OnScopeFirstEntered(); \
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ALLOW_UNUSED_LOCAL( \
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INTERNAL_SCOPED_THREAD_PRIORITY_APPEND_LINE(invoke_once)); \
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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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explicit ScopedMayLoadLibraryAtBackgroundPriority(const Location& from_here);
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~ScopedMayLoadLibraryAtBackgroundPriority();
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// The SCOPED_MAY_LOAD_LIBRARY_AT_BACKGROUND_PRIORITY() macro invokes this the
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// first time that it is encountered.
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bool OnScopeFirstEntered();
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private:
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#if defined(OS_WIN)
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// The original priority when invoking OnScopeFirstEntered().
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base::Optional<ThreadPriority> original_thread_priority_;
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#endif
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DISALLOW_COPY_AND_ASSIGN(ScopedMayLoadLibraryAtBackgroundPriority);
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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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