# content-tracing

`content-trace` 모듈은 Chromium 컨텐츠 모듈단에서 생성된 데이터를 수집하고 추적하는데 사용됩니다.
이 모듈은 웹 인터페이스를 포함하고 있지 않으며 크롬 브라우저에서 `chrome://tracing/` 페이지를 열어 생성된 파일을 로드하면 결과를 볼 수 있습니다.

```javascript
var tracing = require('content-tracing');
tracing.startRecording('*', tracing.DEFAULT_OPTIONS, function() {
  console.log('Tracing started');

  setTimeout(function() {
    tracing.stopRecording('', function(path) {
      console.log('Tracing data recorded to ' + path);
    });
  }, 5000);
});
```

## tracing.getCategories(callback)

* `callback` Function

Get a set of category groups. The category groups can change as new code paths
are reached.

Once all child processes have acked to the `getCategories` request, `callback`
is invoked with an array of category groups.

## tracing.startRecording(categoryFilter, options, callback)

* `categoryFilter` String
* `options` Integer
* `callback` Function

Start recording on all processes.

Recording begins immediately locally, and asynchronously on child processes
as soon as they receive the EnableRecording request. Once all child processes
have acked to the `startRecording` request, `callback` will be called back.

`categoryFilter` is a filter to control what category groups should be
traced. A filter can have an optional `-` prefix to exclude category groups
that contain a matching category. Having both included and excluded
category patterns in the same list is not supported.

Examples:

* `test_MyTest*`,
* `test_MyTest*,test_OtherStuff`,
* `"-excluded_category1,-excluded_category2`

`options` controls what kind of tracing is enabled, it could be a OR-ed
combination of `tracing.DEFAULT_OPTIONS`, `tracing.ENABLE_SYSTRACE`,
`tracing.ENABLE_SAMPLING` and `tracing.RECORD_CONTINUOUSLY`.

## tracing.stopRecording(resultFilePath, callback)

* `resultFilePath` String
* `callback` Function

Stop recording on all processes.

Child processes typically are caching trace data and only rarely flush and send
trace data back to the main process. That is because it may be an expensive
operation to send the trace data over IPC, and we would like to avoid much
runtime overhead of tracing. So, to end tracing, we must asynchronously ask all
child processes to flush any pending trace data.

Once all child processes have acked to the `stopRecording` request, `callback`
will be called back with a file that contains the traced data.

Trace data will be written into `resultFilePath` if it is not empty, or into a
temporary file. The actual file path will be passed to `callback` if it's not
null.

## tracing.startMonitoring(categoryFilter, options, callback)

* `categoryFilter` String
* `options` Integer
* `callback` Function

Start monitoring on all processes.

Monitoring begins immediately locally, and asynchronously on child processes as
soon as they receive the `startMonitoring` request.

Once all child processes have acked to the `startMonitoring` request,
`callback` will be called back.

## tracing.stopMonitoring(callback);

* `callback` Function

Stop monitoring on all processes.

Once all child processes have acked to the `stopMonitoring` request, `callback`
is called back.

## tracing.captureMonitoringSnapshot(resultFilePath, callback)

* `resultFilePath` String
* `callback` Function

Get the current monitoring traced data.

Child processes typically are caching trace data and only rarely flush and send
trace data back to the main process. That is because it may be an expensive
operation to send the trace data over IPC, and we would like to avoid unneeded 
runtime overhead of tracing. So, to end tracing, we must asynchronously ask all
child processes to flush any pending trace data.

Once all child processes have acked to the `captureMonitoringSnapshot` request,
the `callback` will be invoked with a file that contains the traced data.


## tracing.getTraceBufferUsage(callback)

* `callback` Function

Get the maximum across processes of trace buffer percent full state. When the
TraceBufferUsage value is determined, the `callback` is called.

## tracing.setWatchEvent(categoryName, eventName, callback)

* `categoryName` String
* `eventName` String
* `callback` Function

`callback` will will be called every time the given event occurs on any
process.

## tracing.cancelWatchEvent()

Cancel the watch event. If tracing is enabled, this may race with the watch
event callback.