c83f836faf
* docs: add references to app.whenReady() in isReady
* refactor: prefer app.whenReady()
In the docs, specs, and lib, replace instances of `app.once('ready')`
(seen occasionally) and `app.on('ready')` (extremely common) with
`app.whenReady()`.
It's better to encourage users to use whenReady():
1. it handles the edge case of registering for 'ready' after it's fired
2. it avoids the minor wart of leaving an active listener alive for
an event that wll never fire again
86 lines
3.1 KiB
Markdown
86 lines
3.1 KiB
Markdown
# contentTracing
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> Collect tracing data from Chromium to find performance bottlenecks and slow operations.
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Process: [Main](../glossary.md#main-process)
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This module does not include a web interface. To view recorded traces, use
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[trace viewer][], available at `chrome://tracing` in Chrome.
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**Note:** You should not use this module until the `ready` event of the app
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module is emitted.
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```javascript
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const { app, contentTracing } = require('electron')
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app.whenReady().then(() => {
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(async () => {
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await contentTracing.startRecording({
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include_categories: ['*']
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})
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console.log('Tracing started')
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await new Promise(resolve => setTimeout(resolve, 5000))
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const path = await contentTracing.stopRecording()
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console.log('Tracing data recorded to ' + path)
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})()
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})
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```
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## Methods
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The `contentTracing` module has the following methods:
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### `contentTracing.getCategories()`
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Returns `Promise<String[]>` - resolves with an array of category groups once all child processes have acknowledged the `getCategories` request
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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. See also the [list of built-in tracing
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categories](https://chromium.googlesource.com/chromium/src/+/master/base/trace_event/builtin_categories.h).
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> **NOTE:** Electron adds a non-default tracing category called `"electron"`.
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> This category can be used to capture Electron-specific tracing events.
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### `contentTracing.startRecording(options)`
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* `options` ([TraceConfig](structures/trace-config.md) | [TraceCategoriesAndOptions](structures/trace-categories-and-options.md))
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Returns `Promise<void>` - resolved once all child processes have acknowledged the `startRecording` request.
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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.
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If a recording is already running, the promise will be immediately resolved, as
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only one trace operation can be in progress at a time.
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### `contentTracing.stopRecording([resultFilePath])`
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* `resultFilePath` String (optional)
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Returns `Promise<String>` - resolves with a path to a file that contains the traced data once all child processes have acknowledged the `stopRecording` request
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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, Chromium asynchronously asks all child processes to flush any
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pending trace data.
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Trace data will be written into `resultFilePath`. If `resultFilePath` is empty
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or not provided, trace data will be written to a temporary file, and the path
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will be returned in the promise.
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### `contentTracing.getTraceBufferUsage()`
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Returns `Promise<Object>` - Resolves with an object containing the `value` and `percentage` of trace buffer maximum usage
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* `value` Number
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* `percentage` Number
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Get the maximum usage across processes of trace buffer as a percentage of the
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full state.
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[trace viewer]: https://github.com/catapult-project/catapult/blob/master/tracing
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