base/trace_event/trace_sampling_thread.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 "base/trace_event/trace_sampling_thread.h"
#include "base/trace_event/trace_event_impl.h"
#include "base/trace_event/trace_log.h"

namespace base {
namespace trace_event {

class TraceBucketData {
 public:
  TraceBucketData(base::subtle::AtomicWord* bucket,
                  const char* name,
                  TraceSampleCallback callback);
  ~TraceBucketData();

  TRACE_EVENT_API_ATOMIC_WORD* bucket;
  const char* bucket_name;
  TraceSampleCallback callback;
};

TraceSamplingThread::TraceSamplingThread()
    : thread_running_(false), waitable_event_for_testing_(false, false) {}

TraceSamplingThread::~TraceSamplingThread() {}

void TraceSamplingThread::ThreadMain() {
  PlatformThread::SetName("Sampling Thread");
  thread_running_ = true;
  const int kSamplingFrequencyMicroseconds = 1000;
  while (!cancellation_flag_.IsSet()) {
    PlatformThread::Sleep(
        TimeDelta::FromMicroseconds(kSamplingFrequencyMicroseconds));
    GetSamples();
    waitable_event_for_testing_.Signal();
  }
}

// static
void TraceSamplingThread::DefaultSamplingCallback(
    TraceBucketData* bucket_data) {
  TRACE_EVENT_API_ATOMIC_WORD category_and_name =
      TRACE_EVENT_API_ATOMIC_LOAD(*bucket_data->bucket);
  if (!category_and_name)
    return;
  const char* const combined =
      reinterpret_cast<const char* const>(category_and_name);
  const char* category_group;
  const char* name;
  ExtractCategoryAndName(combined, &category_group, &name);
  TRACE_EVENT_API_ADD_TRACE_EVENT(
      TRACE_EVENT_PHASE_SAMPLE,
      TraceLog::GetCategoryGroupEnabled(category_group), name, 0, 0, NULL, NULL,
      NULL, NULL, 0);
}

void TraceSamplingThread::GetSamples() {
  for (size_t i = 0; i < sample_buckets_.size(); ++i) {
    TraceBucketData* bucket_data = &sample_buckets_[i];
    bucket_data->callback.Run(bucket_data);
  }
}

void TraceSamplingThread::RegisterSampleBucket(
    TRACE_EVENT_API_ATOMIC_WORD* bucket,
    const char* const name,
    TraceSampleCallback callback) {
  // Access to sample_buckets_ doesn't cause races with the sampling thread
  // that uses the sample_buckets_, because it is guaranteed that
  // RegisterSampleBucket is called before the sampling thread is created.
  DCHECK(!thread_running_);
  sample_buckets_.push_back(TraceBucketData(bucket, name, callback));
}

// static
void TraceSamplingThread::ExtractCategoryAndName(const char* combined,
                                                 const char** category,
                                                 const char** name) {
  *category = combined;
  *name = &combined[strlen(combined) + 1];
}

void TraceSamplingThread::Stop() {
  cancellation_flag_.Set();
}

void TraceSamplingThread::WaitSamplingEventForTesting() {
  waitable_event_for_testing_.Wait();
}

TraceBucketData::TraceBucketData(base::subtle::AtomicWord* bucket,
                                 const char* name,
                                 TraceSampleCallback callback)
    : bucket(bucket), bucket_name(name), callback(callback) {}

TraceBucketData::~TraceBucketData() {}

}  // namespace trace_event
}  // namespace base