Gracefully shutdown process on SIGTERM

[doochik]

We should manually shutdown process if SIGTERM/SIGINT listeners are installed

nodejs docs (https://nodejs.org/dist/latest-v12.x/docs/api/process.html#process_signal_events)

'SIGTERM' and 'SIGINT' have default handlers on non-Windows platforms that reset the terminal mode before exiting with code 128 + signal number. If one of these signals has a listener installed, its default behavior will be removed (Node.js will no longer exit).

tiny-worker docs (https://github.com/avoidwork/tiny-worker#faq)

In your core script register a listener for SIGTERM or SIGINT via process.on() which terminates (all) worker process(es) and then gracefully shutdowns via process.exit(0);

Example:
Problem: cluster workers don't shutdown because theads.js has invalid SIGTERM listener.

// cluster.js

const cluster = require('cluster');

if (cluster.isMaster) {
    console.log(`Master ${ process.pid } is running`);

    cluster.fork();

    cluster.on('exit', (worker, code, signal) => {
        console.log(`worker ${ worker.process.pid } died`);
    });
} else {
    const { spawn, Worker } = require('threads');

    spawn(new Worker('./worker.js'));
    console.log(`Worker ${ process.pid } started`);
}

// worker.js

const { expose } = require('threads/worker');

expose(() => 'hello from worker');

Run

$ node --version
v12.14.1
$ node cluster.js
Master 64701 is running
Worker 64702 started

$ kill 64702
# nothing happens... But we should see "worker 64702 died"
# PR fixes this problem

[andywer]

Sorry, have been sick for the last two weeks. Good point and thanks for the PR!

I just changed the name of terminateAll to reflect its broadened purpose.

[doochik]

Thanks!