node-epics-ca

EPICS Channel Access client for Node.js

node-epics-ca is lightweight EPICS Channel Access client library for Node.js, it is a FFI (Foreign Function Interface) implementation that talks to the existing EPICS Channel Access shared libraries using a third-party Node.js FFI package called koffi.

This project borrows ideas, implementations and the shared libraries from the following projects,

https://github.com/RobbieClarken/node-epics

https://github.com/onichandame/epics-ioc-connection

https://github.com/pyepics/pyepics

Requirements

A recent Node.js version is required and the following versions have been tested,

• Node.js 12.22.12

• Node.js 14.21.3

• Node.js 15.14.0

• Node.js 16.19.0

• Node.js 17.9.1

• Node.js 18.13.0

Supported platforms

• Windows x86_64

• Linux x86_64

• macOS x86_64

Installation

npm install node-epics-ca

NODE_EPICS_CA_LIBCA, NODE_EPICS_CA_PEND_IO_DELAY or NODE_EPICS_CA_PEND_EVENT_DELAY can be set optionally, for example,

export NODE_EPICS_CA_LIBCA=/home/debian/epics/base-3.15.9/lib/linux-x86_64/libca.so
export NODE_EPICS_CA_PEND_IO_DELAY=1
export NODE_EPICS_CA_PEND_EVENT_DELAY=0.1

If NODE_EPICS_CA_LIBCA is not specified, the os-specific shared libraries in the clibs directory will be used, and which one to use depends on the operating system.

Usage

Approach 1: Simple functions like caget, caput, camonitor and cainfo

get

const CA = require('node-epics-ca');
(async () => {
    try {
        console.log(await CA.get('calcExample'));
    } catch (error) {
        console.error(`get failed due to ${error}`)
    }
})()

put

const CA = require('node-epics-ca');
(async () => {
    try {
        console.log(await CA.get('calcExample'));
        await CA.put("calcExample", 10);
        console.log(await CA.get('calcExample'));
    } catch (error) {
        console.error(`put failed due to ${error}`)
    }
})()

monitor

const CA = require('node-epics-ca');
(async () => {
    let pv = await CA.monitor('calcExample');
    pv.on('value', function(data) {
        console.log('Current:', data);
    });
    // Test purpose only, prevent the node.js main thread from exiting
    setTimeout(function() {
        console.log("Done!!!");
    }, 3600 * 1000);
})()

simpler way for monitor

const CA = require('node-epics-ca');
(async () => {
    CA.monitor('calcExample', function(data) {
        console.log('Current:', data);
    });
    setTimeout(function() {
        console.log("Done!!!");
    }, 3600 * 1000);
})()

info

const CA = require('node-epics-ca');
(async () => {
    try {
        let result = await CA.info('calcExample');
        console.log(`name: ${result.name}`);
        console.log(`state: ${result.state}`);
        console.log(`host: ${result.host}`);
        console.log(`readAccess: ${result.readAccess}`);
        console.log(`writeAccess: ${result.writeAccess}`);
        console.log(`fieldType: ${result.fieldType}`);
        console.log(`elementCount: ${result.elementCount}`);
    } catch (error) {
        console.log(error);
    }
})()

Approach 2: Channel class

get

const CA = require('node-epics-ca');
let pv = new CA.Channel('calcExample');
(async () => {
    try {
        await pv.connect();
        let value = await pv.get();
        console.log(value);
        await pv.disconnect()
    } catch (error) {
        console.log(error);
    }
})()

put

const CA = require('node-epics-ca');
(async () => {
    try {
        let value;
        const pv = new CA.Channel('calcExample');
        await pv.connect();
        value = await pv.get();
        console.log(value);
        await pv.put(10);
        value = await pv.get();
        console.log(value);
        await pv.disconnect()
    } catch (error) {
        console.log(error);
    }
})()

monitor

const CA = require('node-epics-ca');
let pv = new CA.Channel('calcExample');
pv.create();
pv.on('monitor', function() {
    pv.monitor();
});
pv.on('value', function(data) {
    console.log('Current:', data);
});
// Test purpose only, prevent the node.js main thread from exiting
setTimeout(function() {
    console.log("Done!!!");
}, 3600 * 1000);

info

const CA = require('node-epics-ca');
let pv = new CA.Channel('calcExample');
(async () => {
    try {
        await pv.connect();
        let result = pv.info();
        console.log(`name: ${result.name}`);
        console.log(`state: ${result.state}`);
        console.log(`host: ${result.host}`);
        console.log(`readAccess: ${result.readAccess}`);
        console.log(`writeAccess: ${result.writeAccess}`);
        console.log(`fieldType: ${result.fieldType}`);
        console.log(`elementCount: ${result.elementCount}`);
        await pv.disconnect()
    } catch (error) {
        console.log(error);
    }
})()

As string value

get

const CA = require('node-epics-ca');
(async () => {
    try {
        console.log(await CA.get('calcExample', true));
    } catch (error) {
        console.error(`get failed due to ${error}`);
    }
})()

put

const CA = require('node-epics-ca');
(async () => {
    try {
        console.log(await CA.get('calcExample'));
        await CA.put("calcExample", 'One', true);
        console.log(await CA.get('calcExample'));
    } catch (error) {
        console.error(`put failed due to ${error}`);
    }
})()

monitor

const CA = require('node-epics-ca');
(async () => {
    CA.monitor('calcExample', function(data) {
        console.log('Current:', data);
    }, true);
    // Test purpose only, prevent the node.js main thread from exiting
    setTimeout(function() {
        console.log("Done!!!");
    }, 3600 * 1000);
})()

Performance

Performance test for caget, caput, camonitor and cainfo

Number of PVs	caget (seconds)	caput (seconds)	cainfo(seconds)	camonitor (seconds)
1	0.045	0.048	0.037	0.001
10	0.279	0.286	0.282	0.001
50	1.367	1.366	1.363	0.003
100	2.724	2.730	2.719	0.004
200	5.446	5.443	5.439	0.007
500	13.611	13.588	13.582	0.014

Performance test for single caget

Measurement for caget	Time in seconds
create()	0
connect()	0.033
get()	0.005
disconnect()	0.003

The test environment is as follows, the client and IOC are in different virtual machines and different subsets.

• Debian Linux 10 (buster)

• Intel Core Processor (Haswell), 4-core, 2.4GHz

• 8GB memory

Note

Limitation of camonitor

koffi package has limitation for callback count, the maximum is 1024 in version 2.3.20 and increases to 8192 in version 2.3.21-beta.2.

In order to monitor one PV, two callbacks are needed, they are connection state change callback and value change callback, which means only 512 PVs can be monitored at the same if maximum callback is 1024 and 4096 PVs if maximum is 8192.

License

MIT license