测量经过时间

为了更方便地测量操作耗时，我们为 JavaScript 和 C++ 提供了辅助函数。这些辅助函数将经过时间记录到直方图中，因此您需要首先为其创建合适的 直方图。

从 JavaScript 中

JavaScript 可以使用 TelemetryStopwatch 测量经过时间。

TelemetryStopwatch 是一个简化将经过时间（以毫秒为单位）记录到直方图（普通或键控）中的辅助函数。

API

TelemetryStopwatch = {
  // Start, check if running, cancel & finish recording elapsed time into a
  // histogram.
  // |aObject| is optional. If specified, the timer is associated with this
  // object, so multiple time measurements can be done concurrently.
  start(histogramId, aObject);
  running(histogramId, aObject);
  cancel(histogramId, aObject);
  finish(histogramId, aObject);
  // Start, check if running, cancel & finish recording elapsed time into a
  // keyed histogram.
  // |key| specifies the key to record into.
  // |aObject| is optional and used as above.
  startKeyed(histogramId, key, aObject);
  runningKeyed(histogramId, key, aObject);
  cancelKeyed(histogramId, key, aObject);
  finishKeyed(histogramId, key, aObject);
};

示例

TelemetryStopwatch.start("SAMPLE_FILE_LOAD_TIME_MS");
// ... start loading file.
if (failedToOpenFile) {
  // Cancel this if the operation failed early etc.
  TelemetryStopwatch.cancel("SAMPLE_FILE_LOAD_TIME_MS");
  return;
}
// ... do more work.
TelemetryStopwatch.finish("SAMPLE_FILE_LOAD_TIME_MS");

// Another loading attempt? Start stopwatch again if
// not already running.
if (!TelemetryStopwatch.running("SAMPLE_FILE_LOAD_TIME_MS")) {
  TelemetryStopwatch.start("SAMPLE_FILE_LOAD_TIME_MS");
}

// Periodically, it's necessary to attempt to finish a
// TelemetryStopwatch that's already been canceled or
// finished. Normally, that throws a warning to the
// console. If the TelemetryStopwatch being possibly
// canceled or finished is expected behaviour, the
// warning can be suppressed by passing the optional
// aCanceledOkay argument.

// ... suppress warning on a previously finished
// TelemetryStopwatch
TelemetryStopwatch.finish("SAMPLE_FILE_LOAD_TIME_MS", null,
                          true /* aCanceledOkay */);

从 C++ 中

API

// This helper class is the preferred way to record elapsed time.
template<HistogramID id>
class AutoTimer {
  // Record into a plain histogram.
  explicit AutoTimer(TimeStamp aStart = TimeStamp::Now());
  // Record into a keyed histogram, with key |aKey|.
  explicit AutoTimer(const nsCString& aKey,
                     TimeStamp aStart = TimeStamp::Now());
};

// If the Histogram id is not known at compile time:
class RuntimeAutoTimer {
  // Record into a plain histogram.
  explicit RuntimeAutoTimer(Telemetry::HistogramID aId,
                        TimeStamp aStart = TimeStamp::Now());
  // Record into a keyed histogram, with key |aKey|.
  explicit RuntimeAutoTimer(Telemetry::HistogramID aId,
                        const nsCString& aKey,
                        TimeStamp aStart = TimeStamp::Now());
};

void AccumulateTimeDelta(HistogramID id, TimeStamp start, TimeStamp end = TimeStamp::Now());
void AccumulateTimeDelta(HistogramID id, const nsCString& key, TimeStamp start, TimeStamp end = TimeStamp::Now());

示例

{
  Telemetry::AutoTimer<Telemetry::FIND_PLUGINS> telemetry;
  // ... scan disk for plugins.
}
// When leaving the scope, AutoTimers destructor will record the time that passed.

// If the histogram id is not known at compile time.
{
  Telemetry::RuntimeAutoTimer telemetry(Telemetry::FIND_PLUGINS);
  // ... scan disk for plugins.
}
// When leaving the scope, AutoTimers destructor will record the time that passed.