IPC shared memory for Node.js
Use as Buffer or TypedArray
Supports System V and POSIX shared memory

Install

1$ npm install shm-typed-array

Windows is not supported.

System V vs POSIX

Versions 0.0.* support only System V memory segments.
Starting from version 0.1.0 POSIX memory objects are also supported.

System V is the classic way to use shared memory, stores IPC objects internally in the kernel.
POSIX is newer, but not fully supported in MacOS, uses the file system interface.

To create POSIX memory objects, use string parameter key in API.
Eg. shm.create(100, 'Buffer', '/test') will create virtual file /dev/shm/test in tmpfs for Linix.

To create System V memory segment, use numeric parameter key in API.
Eg. shm.create(100, 'Buffer', 1234) or shm.create(100) to autogenerate key.

API

shm.create (count, typeKey, key?, perm?)

Create shared memory segment/object.
count - number of elements (not bytes),
typeKey - type of elements ('Buffer' by default, see list below),
key - integer/null to create System V memory segment, or string to create POSIX memory object,
perm - permissions flag (default is 660).
Returns shared memory Buffer or descendant of TypedArray object, class depends on param typeKey.
Or returns null if shm already exists with provided key.
For System V: returned object has property key - integer key of created System V shared memory segment, to use in shm.get(key).
For POSIX: shared memory objects are not automatically destroyed. You should call shm.destroy(key) manually on process cleanup or if you don't need the object anymore.

shm.get (key, typeKey)

Get created shared memory segment/object by key.
Returns null if shm not exists with provided key.

shm.detach (key, forceDestroy?)

Detach shared memory segment/object.
For System V: If there are no other attaches for a segment, it will be destroyed automatically (even if forceDestroy is not true).
For POSIX: Unlike System V segments, POSIX object will not be destroyed automatically. You need to destroy it manually by providing true to forceDestroy argument or using shm.destroy(key).

shm.destroy (key)

Destroy shared memory segment/object.
Same as shm.detach(key, true)

shm.detachAll ()

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

shm.getTotalSize()

Get total size of all used (mapped) shared memory in bytes.

shm.getTotalCreatedSize()

Get total size of all created shared memory in bytes.

shm.LengthMax

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

Types:

1shm.BufferType = {
2	'Buffer': shm.SHMBT_BUFFER,
3	'Int8Array': shm.SHMBT_INT8,
4	'Uint8Array': shm.SHMBT_UINT8,
5	'Uint8ClampedArray': shm.SHMBT_UINT8CLAMPED,
6	'Int16Array': shm.SHMBT_INT16,
7	'Uint16Array': shm.SHMBT_UINT16,
8	'Int32Array': shm.SHMBT_INT32,
9	'Uint32Array': shm.SHMBT_UINT32,
10	'Float32Array': shm.SHMBT_FLOAT32,
11	'Float64Array': shm.SHMBT_FLOAT64,
12};

Cleanup

This library does cleanup of created SHM segments/objects 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:

1shm.detachAll();

Also note that POSIX shared memory objects are not automatically destroyed. You should call shm.destroy('/your_name') manually if you don't need it anymore.

Usage

See example.js

Usage of memory segments:

1const cluster = require('cluster');
2const shm = require('shm-typed-array');
3
4var buf, arr;
5if (cluster.isMaster) {
6	buf = shm.create(4096); //4KB
7	arr = shm.create(1000000*100, 'Float32Array'); //100M floats
8	buf[0] = 1;
9	arr[0] = 10.0;
10	console.log('[Master] Typeof buf:', buf.constructor.name,
11		'Typeof arr:', arr.constructor.name);
12	
13	var worker = cluster.fork();
14	worker.on('online', function() {
15		this.send({ msg: 'shm', bufKey: buf.key, arrKey: arr.key });
16		var i = 0;
17		setInterval(function() {
18			buf[0] += 1;
19			arr[0] /= 2;
20			console.log(i + ' [Master] Set buf[0]=', buf[0],
21				' arr[0]=', arr ? arr[0] : null);
22			i++;
23			if (i == 5) {
24				groupSuicide();
25			}
26		}, 500);
27	});
28} else {
29	process.on('message', function(data) {
30		var msg = data.msg;
31		if (msg == 'shm') {
32			buf = shm.get(data.bufKey);
33			arr = shm.get(data.arrKey, 'Float32Array');
34			console.log('[Worker] Typeof buf:', buf.constructor.name,
35				'Typeof arr:', arr.constructor.name);
36			var i = 0;
37			setInterval(function() {
38				console.log(i + ' [Worker] Get buf[0]=', buf[0],
39					' arr[0]=', arr ? arr[0] : null);
40				i++;
41				if (i == 2) {
42					shm.detach(data.arrKey);
43					arr = null; //otherwise process will drop
44				}
45			}, 500);
46		} else if (msg == 'exit') {
47			process.exit();
48		}
49	});
50}
51
52function groupSuicide() {
53	if (cluster.isMaster) {
54		for (var id in cluster.workers) {
55		    cluster.workers[id].send({ msg: 'exit'});
56		    cluster.workers[id].destroy();
57		}
58		process.exit();
59	}
60}

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