shm-typed-array

IPC shared memory for NodeJs. Use as Buffer or TypedArray.

Usage no npm install needed!

<script type="module">
  import shmTypedArray from 'https://cdn.skypack.dev/shm-typed-array';
</script>

README

IPC shared memory for Node.js
Use as Buffer or TypedArray
npm travis

Install

$ npm install shm-typed-array

Windows is not supported.

API

shm.create (count, typeKey [, key] [, perm])

Create shared memory segment.
count - number of elements (not bytes), typeKey - type of elements ('Buffer' by default, see list below), key - optional integer to create shm with specific key, perm - optional permissions flag (default is 660). Returns shared memory Buffer or descendant of TypedArray object, class depends on param typeKey.
Or returns null if shm can't be created.
Returned object has property key - integer key of created shared memory segment, to use in shm.get().

shm.get (key, typeKey)

Get created shared memory segment. Returns null if shm can't be opened.

shm.detach (key [, forceDestroy])

Detach shared memory segment.
If there are no other attaches for this segment (or forceDestroy is true), it will be destroyed.

shm.detachAll ()

Detach all created shared memory segments.
Will be automatically called on process exit, see Cleanup.

Types:

shm.BufferType = {
    'Buffer': shm.SHMBT_BUFFER,
    'Int8Array': shm.SHMBT_INT8,
    'Uint8Array': shm.SHMBT_UINT8,
    'Uint8ClampedArray': shm.SHMBT_UINT8CLAMPED,
    'Int16Array': shm.SHMBT_INT16,
    'Uint16Array': shm.SHMBT_UINT16,
    'Int32Array': shm.SHMBT_INT32,
    'Uint32Array': shm.SHMBT_UINT32,
    'Float32Array': shm.SHMBT_FLOAT32,
    'Float64Array': shm.SHMBT_FLOAT64,
};

shm.getTotalSize()

Get total size of all shared segments in bytes.

shm.LengthMax

Max length of shared memory segment (count of elements, not bytes)
2^31 for 64bit, 2^30 for 32bit

Cleanup

This library does cleanup of created SHM segments only on normal exit of process, see exit event.
If you want to do cleanup on terminate signals like SIGINT, SIGTERM, please use node-cleanup / node-death and add code to exit handlers:

shm.detachAll();

Usage

See example.js

const cluster = require('cluster');
const shm = require('shm-typed-array');

var buf, arr;
if (cluster.isMaster) {
    buf = shm.create(4096); //4KB
    arr = shm.create(1000000*100, 'Float32Array'); //100M floats
    buf[0] = 1;
    arr[0] = 10.0;
    console.log('[Master] Typeof buf:', buf.constructor.name,
        'Typeof arr:', arr.constructor.name);
    
    var worker = cluster.fork();
    worker.on('online', function() {
        this.send({ msg: 'shm', bufKey: buf.key, arrKey: arr.key });
        var i = 0;
        setInterval(function() {
            buf[0] += 1;
            arr[0] /= 2;
            console.log(i + ' [Master] Set buf[0]=', buf[0],
                ' arr[0]=', arr ? arr[0] : null);
            i++;
            if (i == 5) {
                groupSuicide();
            }
        }, 500);
    });
} else {
    process.on('message', function(data) {
        var msg = data.msg;
        if (msg == 'shm') {
            buf = shm.get(data.bufKey);
            arr = shm.get(data.arrKey, 'Float32Array');
            console.log('[Worker] Typeof buf:', buf.constructor.name,
                'Typeof arr:', arr.constructor.name);
            var i = 0;
            setInterval(function() {
                console.log(i + ' [Worker] Get buf[0]=', buf[0],
                    ' arr[0]=', arr ? arr[0] : null);
                i++;
                if (i == 2) {
                    shm.detach(data.arrKey);
                    arr = null; //otherwise process will drop
                }
            }, 500);
        } else if (msg == 'exit') {
            process.exit();
        }
    });
}

function groupSuicide() {
    if (cluster.isMaster) {
        for (var id in cluster.workers) {
            cluster.workers[id].send({ msg: 'exit'});
            cluster.workers[id].destroy();
        }
        process.exit();
    }
}

Output:

[Master] Typeof buf: Buffer Typeof arr: Float32Array
[Worker] Typeof buf: Buffer Typeof arr: Float32Array
0 [Master] Set buf[0]= 2  arr[0]= 5
0 [Worker] Get buf[0]= 2  arr[0]= 5
1 [Master] Set buf[0]= 3  arr[0]= 2.5
1 [Worker] Get buf[0]= 3  arr[0]= 2.5
2 [Master] Set buf[0]= 4  arr[0]= 1.25
2 [Worker] Get buf[0]= 4  arr[0]= null
3 [Master] Set buf[0]= 5  arr[0]= 0.625
3 [Worker] Get buf[0]= 5  arr[0]= null
4 [Master] Set buf[0]= 6  arr[0]= 0.3125
shm segments destroyed: 2