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Viewing / Editing File: trace_events.d.ts

/**
 * The `trace_events` module provides a mechanism to centralize tracing information
 * generated by V8, Node.js core, and userspace code.
 *
 * Tracing can be enabled with the `--trace-event-categories` command-line flag
 * or by using the `trace_events` module. The `--trace-event-categories` flag
 * accepts a list of comma-separated category names.
 *
 * The available categories are:
 *
 * * `node`: An empty placeholder.
 * * `node.async_hooks`: Enables capture of detailed `async_hooks` trace data.
 * The `async_hooks` events have a unique `asyncId` and a special `triggerId` `triggerAsyncId` property.
 * * `node.bootstrap`: Enables capture of Node.js bootstrap milestones.
 * * `node.console`: Enables capture of `console.time()` and `console.count()`output.
 * * `node.dns.native`: Enables capture of trace data for DNS queries.
 * * `node.environment`: Enables capture of Node.js Environment milestones.
 * * `node.fs.sync`: Enables capture of trace data for file system sync methods.
 * * `node.perf`: Enables capture of `Performance API` measurements.
 *    * `node.perf.usertiming`: Enables capture of only Performance API User Timing
 *    measures and marks.
 *    * `node.perf.timerify`: Enables capture of only Performance API timerify
 *    measurements.
 * * `node.promises.rejections`: Enables capture of trace data tracking the number
 * of unhandled Promise rejections and handled-after-rejections.
 * * `node.vm.script`: Enables capture of trace data for the `vm` module's`runInNewContext()`, `runInContext()`, and `runInThisContext()` methods.
 * * `v8`: The `V8` events are GC, compiling, and execution related.
 *
 * By default the `node`, `node.async_hooks`, and `v8` categories are enabled.
 *
 * ```bash
 * node --trace-event-categories v8,node,node.async_hooks server.js
 * ```
 *
 * Prior versions of Node.js required the use of the `--trace-events-enabled`flag to enable trace events. This requirement has been removed. However, the`--trace-events-enabled` flag _may_ still be
 * used and will enable the`node`, `node.async_hooks`, and `v8` trace event categories by default.
 *
 * ```bash
 * node --trace-events-enabled
 *
 * # is equivalent to
 *
 * node --trace-event-categories v8,node,node.async_hooks
 * ```
 *
 * Alternatively, trace events may be enabled using the `trace_events` module:
 *
 * ```js
 * const trace_events = require('trace_events');
 * const tracing = trace_events.createTracing({ categories: ['node.perf'] });
 * tracing.enable();  // Enable trace event capture for the 'node.perf' category
 *
 * // do work
 *
 * tracing.disable();  // Disable trace event capture for the 'node.perf' category
 * ```
 *
 * Running Node.js with tracing enabled will produce log files that can be opened
 * in the [`chrome://tracing`](https://www.chromium.org/developers/how-tos/trace-event-profiling-tool) tab of Chrome.
 *
 * The logging file is by default called `node_trace.${rotation}.log`, where`${rotation}` is an incrementing log-rotation id. The filepath pattern can
 * be specified with `--trace-event-file-pattern` that accepts a template
 * string that supports `${rotation}` and `${pid}`:
 *
 * ```bash
 * node --trace-event-categories v8 --trace-event-file-pattern '${pid}-${rotation}.log' server.js
 * ```
 *
 * The tracing system uses the same time source
 * as the one used by `process.hrtime()`.
 * However the trace-event timestamps are expressed in microseconds,
 * unlike `process.hrtime()` which returns nanoseconds.
 *
 * The features from this module are not available in `Worker` threads.
 * @experimental
 * @see [source](https://github.com/nodejs/node/blob/v17.0.0/lib/trace_events.js)
 */
declare module 'trace_events' {
    /**
     * The `Tracing` object is used to enable or disable tracing for sets of
     * categories. Instances are created using the
     * `trace_events.createTracing()` method.
     *
     * When created, the `Tracing` object is disabled. Calling the
     * `tracing.enable()` method adds the categories to the set of enabled trace
     * event categories. Calling `tracing.disable()` will remove the categories
     * from the set of enabled trace event categories.
     */
    interface Tracing {
        /**
         * A comma-separated list of the trace event categories covered by this
         * `Tracing` object.
         */
        readonly categories: string;
        /**
         * Disables this `Tracing` object.
         *
         * Only trace event categories _not_ covered by other enabled `Tracing`
         * objects and _not_ specified by the `--trace-event-categories` flag
         * will be disabled.
         */
        disable(): void;
        /**
         * Enables this `Tracing` object for the set of categories covered by
         * the `Tracing` object.
         */
        enable(): void;
        /**
         * `true` only if the `Tracing` object has been enabled.
         */
        readonly enabled: boolean;
    }
    interface CreateTracingOptions {
        /**
         * An array of trace category names. Values included in the array are
         * coerced to a string when possible. An error will be thrown if the
         * value cannot be coerced.
         */
        categories: string[];
    }
    /**
     * Creates and returns a `Tracing` object for the given set of `categories`.
     *
     * ```js
     * const trace_events = require('trace_events');
     * const categories = ['node.perf', 'node.async_hooks'];
     * const tracing = trace_events.createTracing({ categories });
     * tracing.enable();
     * // do stuff
     * tracing.disable();
     * ```
     * @since v10.0.0
     * @return .
     */
    function createTracing(options: CreateTracingOptions): Tracing;
    /**
     * Returns a comma-separated list of all currently-enabled trace event
     * categories. The current set of enabled trace event categories is determined
     * by the _union_ of all currently-enabled `Tracing` objects and any categories
     * enabled using the `--trace-event-categories` flag.
     *
     * Given the file `test.js` below, the command`node --trace-event-categories node.perf test.js` will print`'node.async_hooks,node.perf'` to the console.
     *
     * ```js
     * const trace_events = require('trace_events');
     * const t1 = trace_events.createTracing({ categories: ['node.async_hooks'] });
     * const t2 = trace_events.createTracing({ categories: ['node.perf'] });
     * const t3 = trace_events.createTracing({ categories: ['v8'] });
     *
     * t1.enable();
     * t2.enable();
     *
     * console.log(trace_events.getEnabledCategories());
     * ```
     * @since v10.0.0
     */
    function getEnabledCategories(): string | undefined;
}
declare module 'node:trace_events' {
    export * from 'trace_events';
}

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