DevTools: Initial implementation of slow CPU emulation.

content/renderer/devtools/devtools_cpu_throttler.cc

+// Copyright 2015 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 "content/renderer/devtools/devtools_cpu_throttler.h"
+
+#if defined(OS_POSIX)
+#include <signal.h>
+#define USE_SIGNALS
+#endif
+
+#include "base/atomicops.h"
+#include "base/synchronization/cancellation_flag.h"
+#include "base/threading/platform_thread.h"
+
+using base::subtle::Atomic32;
+using base::subtle::Acquire_Load;
+using base::subtle::Release_Store;
+
+namespace content {
+
+class CPUThrottlingThread final : public base::PlatformThread::Delegate {
+ public:
+  CPUThrottlingThread(double rate);

[pfeldman, 2015/12/12 00:33:18]

explicit

+  ~CPUThrottlingThread() override;
+
+  void SetThrottlingRate(double rate);
+
+  void ThreadMain() override;
+
+ private:
+  void Start();
+  void Stop();
+  void Throttle();
+
+  static void SuspendThread(base::PlatformThreadHandle thread_handle);
+  static void ResumeThread(base::PlatformThreadHandle thread_handle);
+
+#ifdef USE_SIGNALS
+  void InstallSignalHandler();
+  void RestoreSignalHandler();
+  static void HandleSignal(int signal);
+
+  static bool signal_handler_installed_;
+  static struct sigaction old_signal_handler_;
+  static Atomic32 suspended_;
+#endif
+  static Atomic32 thread_exists_;
+
+  base::PlatformThreadHandle throttled_thread_handle_;
+  base::PlatformThreadHandle throttling_thread_handle_;
+  base::CancellationFlag cancellation_flag_;
+  Atomic32 throttling_rate_percent_;
+
+  DISALLOW_COPY_AND_ASSIGN(CPUThrottlingThread);
+};
+
+#ifdef USE_SIGNALS
+bool CPUThrottlingThread::signal_handler_installed_;
+struct sigaction CPUThrottlingThread::old_signal_handler_;
+Atomic32 CPUThrottlingThread::suspended_;
+#endif
+Atomic32 CPUThrottlingThread::thread_exists_;
+
+CPUThrottlingThread::CPUThrottlingThread(double rate)
+    : throttled_thread_handle_(base::PlatformThread::CurrentHandle()),
+      throttling_rate_percent_(static_cast<Atomic32>(rate * 100)) {
+  CHECK(base::subtle::NoBarrier_AtomicExchange(&thread_exists_, 1) == 0);
+  Start();
+}
+
+CPUThrottlingThread::~CPUThrottlingThread() {
+  Stop();
+  CHECK(base::subtle::NoBarrier_AtomicExchange(&thread_exists_, 0) == 1);
+}
+
+void CPUThrottlingThread::SetThrottlingRate(double rate) {
+  Release_Store(&throttling_rate_percent_, static_cast<Atomic32>(rate * 100));
+}
+
+void CPUThrottlingThread::ThreadMain() {
+  base::PlatformThread::SetName("DevToolsCPUThrottlingThread");
+  while (!cancellation_flag_.IsSet()) {
+    Throttle();
+  }
+}
+
+#ifdef USE_SIGNALS
+
+// static
+void CPUThrottlingThread::InstallSignalHandler() {
+  // There must be the only one!
+  DCHECK(!signal_handler_installed_);
+  struct sigaction sa;
+  sa.sa_handler = &HandleSignal;
+  sigemptyset(&sa.sa_mask);
+  sa.sa_flags = SA_RESTART;
+  signal_handler_installed_ =
+      (sigaction(SIGUSR2, &sa, &old_signal_handler_) == 0);
+}
+
+// static
+void CPUThrottlingThread::RestoreSignalHandler() {
+  if (!signal_handler_installed_)
+    return;
+  sigaction(SIGUSR2, &old_signal_handler_, 0);
+  signal_handler_installed_ = false;
+}
+
+// static
+void CPUThrottlingThread::HandleSignal(int signal) {
+  if (signal != SIGUSR2)
+    return;
+  while (Acquire_Load(&suspended_)) {
+  }
+}
+
+#endif  // USE_SIGNALS
+
+// static
+void CPUThrottlingThread::SuspendThread(
+    base::PlatformThreadHandle thread_handle) {
+#ifdef USE_SIGNALS
+  Release_Store(&suspended_, 1);
+  pthread_kill(thread_handle.platform_handle(), SIGUSR2);
+#endif
+}
+
+// static
+void CPUThrottlingThread::ResumeThread(
+    base::PlatformThreadHandle thread_handle) {
+#ifdef USE_SIGNALS
+  Release_Store(&suspended_, 0);
+#endif
+}
+
+void CPUThrottlingThread::Start() {
+#ifdef USE_SIGNALS
+  InstallSignalHandler();
+#endif
+  if (!base::PlatformThread::Create(0, this, &throttling_thread_handle_)) {
+    LOG(ERROR) << "Failed to create throttling thread.";
+  }
+}
+
+void CPUThrottlingThread::Stop() {
+  cancellation_flag_.Set();
+  base::PlatformThread::Join(throttling_thread_handle_);
+#ifdef USE_SIGNALS
+  RestoreSignalHandler();
+#endif
+}
+
+void CPUThrottlingThread::Throttle() {
+  const int quant_time_us = 200;
+  double rate = Acquire_Load(&throttling_rate_percent_) / 100.;
+  base::TimeDelta run_duration =
+      base::TimeDelta::FromMicroseconds(static_cast<int>(quant_time_us / rate));
+  base::TimeDelta sleep_duration =
+      base::TimeDelta::FromMicroseconds(quant_time_us) - run_duration;
+  base::PlatformThread::Sleep(run_duration);
+  SuspendThread(throttled_thread_handle_);
+  base::PlatformThread::Sleep(sleep_duration);
+  ResumeThread(throttled_thread_handle_);
+}
+
+DevToolsCPUThrottler::DevToolsCPUThrottler() {}
+
+DevToolsCPUThrottler::~DevToolsCPUThrottler() {}
+
+void DevToolsCPUThrottler::SetThrottlingRate(double rate) {
+  if (rate <= 1) {
+    if (throttling_thread_) {
+      throttling_thread_.reset();
+    }
+    return;
+  }
+  if (throttling_thread_) {
+    throttling_thread_->SetThrottlingRate(rate);
+  } else {
+    throttling_thread_.reset(new CPUThrottlingThread(rate));
+  }
+}
+
+}  // namespace content