157 lines
5.1 KiB
Markdown
157 lines
5.1 KiB
Markdown
# contentTracing
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The `content-tracing` module is used to collect tracing data generated by the
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underlying Chromium content module. This module does not include a web interface
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so you need to open `chrome://tracing/` in a Chrome browser and load the
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generated file to view the result.
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```javascript
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var contentTracing = require('content-tracing');
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contentTracing.startRecording('*', contentTracing.DEFAULT_OPTIONS, function() {
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console.log('Tracing started');
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setTimeout(function() {
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contentTracing.stopRecording('', function(path) {
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console.log('Tracing data recorded to ' + path);
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});
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}, 5000);
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});
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```
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## Methods
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The `content-tracing` module has the following methods:
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### `contentTracing.getCategories(callback)`
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* `callback` Function
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Get a set of category groups. The category groups can change as new code paths
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are reached.
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Once all child processes have acknowledged the `getCategories` request the
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`callback` is invoked with an array of category groups.
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### `contentTracing.startRecording(categoryFilter, traceOptions, callback)`
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* `categoryFilter` String
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* `traceOptions` String
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* `callback` Function
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Start recording on all processes.
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Recording begins immediately locally and asynchronously on child processes
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as soon as they receive the EnableRecording request. The `callback` will be
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called once all child processes have acknowledged the `startRecording` request.
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`categoryFilter` is a filter to control what category groups should be
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traced. A filter can have an optional `-` prefix to exclude category groups
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that contain a matching category. Having both included and excluded
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category patterns in the same list is not supported.
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Examples:
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* `test_MyTest*`,
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* `test_MyTest*,test_OtherStuff`,
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* `"-excluded_category1,-excluded_category2`
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`traceOptions` controls what kind of tracing is enabled, it is a comma-delimited
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list. Possible options are:
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* `record-until-full`
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* `record-continuously`
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* `trace-to-console`
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* `enable-sampling`
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* `enable-systrace`
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The first 3 options are trace recoding modes and hence mutually exclusive.
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If more than one trace recording modes appear in the `traceOptions` string,
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the last one takes precedence. If none of the trace recording modes are
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specified, recording mode is `record-until-full`.
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The trace option will first be reset to the default option (`record_mode` set to
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`record-until-full`, `enable_sampling` and `enable_systrace` set to `false`)
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before options parsed from `traceOptions` are applied on it.
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### `contentTracing.stopRecording(resultFilePath, callback)`
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* `resultFilePath` String
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* `callback` Function
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Stop recording on all processes.
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Child processes typically cache trace data and only rarely flush and send
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trace data back to the main process. This helps to minimize the runtime overhead
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of tracing since sending trace data over IPC can be an expensive operation. So,
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to end tracing, we must asynchronously ask all child processes to flush any
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pending trace data.
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Once all child processes have acknowledged the `stopRecording` request,
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`callback` will be called with a file that contains the traced data.
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Trace data will be written into `resultFilePath` if it is not empty or into a
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temporary file. The actual file path will be passed to `callback` if it's not
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`null`.
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### `contentTracing.startMonitoring(categoryFilter, traceOptions, callback)`
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* `categoryFilter` String
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* `traceOptions` String
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* `callback` Function
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Start monitoring on all processes.
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Monitoring begins immediately locally and asynchronously on child processes as
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soon as they receive the `startMonitoring` request.
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Once all child processes have acknowledged the `startMonitoring` request the
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`callback` will be called.
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### `contentTracing.stopMonitoring(callback)`
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* `callback` Function
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Stop monitoring on all processes.
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Once all child processes have acknowledged the `stopMonitoring` request the
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`callback` is called.
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### `contentTracing.captureMonitoringSnapshot(resultFilePath, callback)`
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* `resultFilePath` String
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* `callback` Function
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Get the current monitoring traced data.
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Child processes typically cache trace data and only rarely flush and send
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trace data back to the main process. This is because it may be an expensive
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operation to send the trace data over IPC and we would like to avoid unneeded
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runtime overhead from tracing. So, to end tracing, we must asynchronously ask
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all child processes to flush any pending trace data.
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Once all child processes have acknowledged the `captureMonitoringSnapshot`
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request the `callback` will be called with a file that contains the traced data.
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### `contentTracing.getTraceBufferUsage(callback)`
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* `callback` Function
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Get the maximum usage across processes of trace buffer as a percentage of the
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full state. When the TraceBufferUsage value is determined the `callback` is
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called.
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### `contentTracing.setWatchEvent(categoryName, eventName, callback)`
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* `categoryName` String
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* `eventName` String
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* `callback` Function
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`callback` will will be called every time the given event occurs on any
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process.
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### `contentTracing.cancelWatchEvent()`
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Cancel the watch event. This may lead to a race condition with the watch event
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callback if tracing is enabled.
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