base/threading/scoped_thread_priority.cc

// 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.

#include "base/threading/scoped_thread_priority.h"

#include "base/containers/flat_set.h"
#include "base/location.h"
#include "base/no_destructor.h"
#include "base/synchronization/lock.h"
#include "base/threading/platform_thread.h"
#include "base/trace_event/trace_event.h"

namespace base {

namespace {

#if defined(OS_WIN)
// Flags the location |from_here| as executed. Returns true if the location
// was not previously executed.
bool ShouldBoostThreadPriorityForLocation(const Location& from_here) {
  using ExecutedProgramCounterSet = base::flat_set<const void*>;
  static base::NoDestructor<base::Lock> lock;
  static base::NoDestructor<ExecutedProgramCounterSet> cache;

  base::AutoLock auto_lock(*lock);
  return cache.get()->insert(from_here.program_counter()).second;
}
#endif  // OS_WIN

}  // namespace

#if defined(OS_WIN)
// Enable the boost of thread priority when the code may load a library. The
// thread priority boost is required to avoid priority inversion on the loader
// lock.
constexpr base::Feature kBoostThreadPriorityOnLibraryLoading{
    "BoostThreadPriorityOnLibraryLoading", base::FEATURE_DISABLED_BY_DEFAULT};
#endif  // OS_WIN

ScopedThreadMayLoadLibraryOnBackgroundThread::
    ScopedThreadMayLoadLibraryOnBackgroundThread(const Location& from_here) {
  TRACE_EVENT_BEGIN2("base", "ScopedThreadMayLoadLibraryOnBackgroundThread",
                     "file_name", from_here.file_name(), "function_name",
                     from_here.function_name());

#if defined(OS_WIN)
  if (!base::FeatureList::IsEnabled(kBoostThreadPriorityOnLibraryLoading))
    return;

  // If the code at |from_here| has already been executed, do not boost the
  // thread priority.
  if (!ShouldBoostThreadPriorityForLocation(from_here))
    return;

  base::ThreadPriority priority = PlatformThread::GetCurrentThreadPriority();
  if (priority == base::ThreadPriority::BACKGROUND) {
    original_thread_priority_ = priority;
    PlatformThread::SetCurrentThreadPriority(base::ThreadPriority::NORMAL);
  }
#endif  // OS_WIN
}

ScopedThreadMayLoadLibraryOnBackgroundThread::
    ~ScopedThreadMayLoadLibraryOnBackgroundThread() {
  TRACE_EVENT_END0("base", "ScopedThreadMayLoadLibraryOnBackgroundThread");
#if defined(OS_WIN)
  if (original_thread_priority_)
    PlatformThread::SetCurrentThreadPriority(original_thread_priority_.value());
#endif  // OS_WIN
}

}  // namespace base