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.

$3

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

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

$3

`js
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gcInfo.off('data', listener1) // listener1 is no longer active but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.
`

$3

`js
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

`js
{
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
}
}
``

$3

- 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+)