Diagnostics Channel

Ajouté en: v15.1.0

Code source: lib/diagnostics_channel.js

The node:diagnostics_channel module provides an API to create named channels to report arbitrary message data for diagnostics purposes.

It can be accessed using:

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It is intended that a module writer wanting to report diagnostics messages will create one or many top-level channels to report messages through. Channels may also be acquired at runtime but it is not encouraged due to the additional overhead of doing so. Channels may be exported for convenience, but as long as the name is known it can be acquired anywhere.

If you intend for your module to produce diagnostics data for others to consume it is recommended that you include documentation of what named channels are used along with the shape of the message data. Channel names should generally include the module name to avoid collisions with data from other modules.

Public API

Overview

Following is a simple overview of the public API.

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M diagnostics_channel.hasSubscribers(name)

Ajouté en: v15.1.0, v14.17.0

• name string | symbol The channel name
• Returns: boolean If there are active subscribers

Check if there are active subscribers to the named channel. This is helpful if the message you want to send might be expensive to prepare.

This API is optional but helpful when trying to publish messages from very performance-sensitive code.

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M diagnostics_channel.channel(name)

Ajouté en: v15.1.0, v14.17.0

• name string | symbol The channel name
• Returns: Channel The named channel object

This is the primary entry-point for anyone wanting to publish to a named channel. It produces a channel object which is optimized to reduce overhead at publish time as much as possible.

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M diagnostics_channel.subscribe(name, onMessage)

Ajouté en: v16.17.0

• name string | symbol The channel name
• onMessage Function The handler to receive channel messages
  • message any The message data
  • name string | symbol The name of the channel

Register a message handler to subscribe to this channel. This message handler will be run synchronously whenever a message is published to the channel. Any errors thrown in the message handler will trigger an 'uncaughtException'.

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M diagnostics_channel.unsubscribe(name, onMessage)

Ajouté en: v16.17.0

• name string | symbol The channel name
• onMessage Function The previous subscribed handler to remove
• Returns: boolean true if the handler was found, false otherwise.

Remove a message handler previously registered to this channel with diagnostics_channel.subscribe(name, onMessage).

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C Channel

Ajouté en: v15.1.0, v14.17.0

The class Channel represents an individual named channel within the data pipeline. It is used to track subscribers and to publish messages when there are subscribers present. It exists as a separate object to avoid channel lookups at publish time, enabling very fast publish speeds and allowing for heavy use while incurring very minimal cost. Channels are created with diagnostics_channel.channel(name), constructing a channel directly with new Channel(name) is not supported.

M channel.hasSubscribers

Ajouté en: v15.1.0, v14.17.0

• Returns: boolean If there are active subscribers

Check if there are active subscribers to this channel. This is helpful if the message you want to send might be expensive to prepare.

This API is optional but helpful when trying to publish messages from very performance-sensitive code.

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M channel.publish(message)

Ajouté en: v15.1.0, v14.17.0

• message any The message to send to the channel subscribers

Publish a message to any subscribers to the channel. This will trigger message handlers synchronously so they will execute within the same context.

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M channel.subscribe(onMessage)

Déprécié en: v16.17.0

• onMessage Function The handler to receive channel messages
  • message any The message data
  • name string | symbol The name of the channel

Register a message handler to subscribe to this channel. This message handler will be run synchronously whenever a message is published to the channel. Any errors thrown in the message handler will trigger an 'uncaughtException'.

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M channel.unsubscribe(onMessage)

• onMessage Function The previous subscribed handler to remove
• Returns: boolean true if the handler was found, false otherwise.

Remove a message handler previously registered to this channel with channel.subscribe(onMessage).

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Built-in Channels

HTTP

http.client.request.start

• request http.ClientRequest

Emitted when client starts a request.

http.client.response.finish

• request http.ClientRequest
• response http.IncomingMessage

Emitted when client receives a response.

http.server.request.start

• request http.IncomingMessage
• response http.ServerResponse
• socket net.Socket
• server http.Server

Emitted when server receives a request.

http.server.response.finish

• request http.IncomingMessage
• response http.ServerResponse
• socket net.Socket
• server http.Server

Emitted when server sends a response.

NET

net.client.socket

• socket net.Socket

Emitted when a new TCP or pipe client socket is created.

net.server.socket

• socket net.Socket

Emitted when a new TCP or pipe connection is received.

UDP

udp.socket

• socket dgram.Socket

Emitted when a new UDP socket is created.

Process

Ajouté en: v16.18.0

child_process

• process ChildProcess

Emitted when a new process is created.

Worker Thread

Ajouté en: v16.18.0

worker_threads

• worker Worker

Emitted when a new thread is created.