gc_info

Gives you information about V8 GC after its execution. Based on gc-stats.

Since version 1.0.0 the module supports all existing Node.js versions since 0.8 to the current release and binaries for Node.js 5+ are provided together; for prior versions module must be compiled.

Since version 1.2.0 the module supports all existing Electron versions since 0.3.1 to the current release and binaries for Electron 0.36.0+ are provided together; for prior versions module must be compiled.

Since version 2.0.0 the module provides binaries only for Node 17+ and Electron 23+; for prior versions module must be compiled.

It is a C++ addon written using the module nan and following the Google C++ Style Guide except for the lint. If you find something not compliant with, please provide a pull request.

In general every pull request that will:

• Let the code be compliant to Google C++ Style Guide
• Improve performances
• Save memory
• Add features

are well accepted.

Usage

Require the module and subscribe the data event.

Basic

const gcInfo = require('@matteodisabatino/gc_info')

gcInfo.on('data', info => {
  console.log('GC information: ', info)
})

Unsubscribe specific listener

const gcInfo = require('@matteodisabatino/gc_info')

const listener1 = info => {
  console.log('listener1 - GC information: ', info)
}

const listener2 = info => {
  console.log('listener2 - GC information: ', info)
}

gcInfo.on('data', listener1)
gcInfo.on('data', listener2)

gcInfo.off('data', listener1) // listener1 is no longer active but
                              // you will still receive data via
                              // listener2.

Unsubscribe all listeners

const gcInfo = require('@matteodisabatino/gc_info')

const listener1 = info => {
  console.log('listener1 - GC information: ', info)
}

const listener2 = info => {
  console.log('listener2 - GC information: ', info)
}

gcInfo.on('data', listener1)
gcInfo.on('data', listener2)

gcInfo.off('data') // Both listener1 and listener2 are no longer
                   // active. You will not receive any data until you
                   // will subscribe the `data` event again.

Information

{
  startedAt: Number,
  endedAt: Number,
  duration: Number,
  gctype: Number,
  pre: {
    totalHeapSize: Number,
    totalHeapSizeExecutable: Number,
    usedHeapSize: Number,
    heapSizeLimit: Number,
    totalPhysicalSize: Number,
    totalAvailableSize: Number,
    mallocedMemory: Number,
    peakMallocedMemory: Number,
    numberOfNativeContexts: Number,
    numberOfDetachedContexts: Number,
    externalMemory: Number,
    totalGlobalHandlesSize: Number,
    usedGlobalHandlesSize: Number
  },
  post: {
    totalHeapSize: Number,
    totalHeapSizeExecutable: Number,
    usedHeapSize: Number,
    heapSizeLimit: Number,
    totalPhysicalSize: Number,
    totalAvailableSize: Number,
    mallocedMemory: Number,
    peakMallocedMemory: Number,
    numberOfNativeContexts: Number,
    numberOfDetachedContexts: Number,
    externalMemory: Number,
    totalGlobalHandlesSize: Number,
    usedGlobalHandlesSize: Number
  },
  diff: {
    totalHeapSize: Number,
    totalHeapSizeExecutable: Number,
    usedHeapSize: Number,
    heapSizeLimit: Number,
    totalPhysicalSize: Number,
    totalAvailableSize: Number,
    mallocedMemory: Number,
    peakMallocedMemory: Number,
    numberOfNativeContexts: Number,
    numberOfDetachedContexts: Number,
    externalMemory: Number,
    totalGlobalHandlesSize: Number,
    usedGlobalHandlesSize: Number
  }
}

Property meaning

• startedAt: The moment the GC started (Unix timestamp in milliseconds).

• endedAt: The moment the GC ended (Unix timestamp in milliseconds).

• duration: The time the GC has been active (difference between endedAt and startedAt).

• gctype: Memory allocation type. According to v8 source code possible values are:

  • 1: Scavenge
  • 2: Mark/Sweep/Compact
  • 4: Incremental marking
  • 8: Weak/Phantom callback processing
  • 15: All

• totalHeapSize: Number of bytes V8 has allocated for the heap. This can grow if usedHeap needs more.

• totalHeapSizeExecutable: Number of bytes for compiled bytecode and JITed code.

• usedHeapSize: Number of bytes in use by application data.

• heapSizeLimit: The absolute limit the heap cannot exceed.

• totalPhysicalSize: Committed size. (Node.js 0.12+)

• totalAvailableSize: Available heap size. (Node.js 4+)

• mallocedMemory: Current amount of memory, obtained via malloc. (Node.js 7+)

• peakMallocedMemory: Peak amount of memory, obtained via malloc. (Node.js 7+)

• numberOfNativeContexts: Number of the top-level contexts currently active. Increase of this number over time indicates a memory leak. (Node.js 10+)

• numberOfDetachedContexts: Number of contexts that were detached and not yet garbage collected. This number being non-zero indicates a potential memory leak. (Node.js 10+)

• externalMemory: Number of bytes of memory allocated outside of v8's heap. (Node.js 12+)

• totalGlobalHandlesSize: Size of all global handles in the heap. (Node.js 14+)

• usedGlobalHandlesSize: Size of all allocated/used global handles in the heap. (Node.js 14+)