bug: Throat causes a halt in execution under certain conditions

[bjornua]

Describe the bug

Throat causes a halt in execution under certain conditions

To Reproduce

const _ = require('lodash');
const throat = require('throat');

async function main() {
  const worker = throat(4, async function (page) {});
  const pagesChunks = _.range(10).map((n) => _.range(100));

  let awaitCount = 0;
  for (const pagesChunk of pagesChunks) {
    console.log(`Await ${awaitCount++}`);
    await Promise.all(pagesChunk.map(worker));
  }

  console.log('Done');
}

main();

This outputs:

Await 0
Await 1
Await 2

Expected behaviour

Expected output:

Await 0
Await 1
Await 2
Await 3
Await 4
Await 5
Await 6
Await 7
Await 8
Await 9
Done

Versions

• node version: v14.17.5
• npm/yarn version: 6.14.14
• package version: throat-6.0.1

Additional context

Messing around with the length of pagesChunk or size can make the script complete normally, or halt earlier or later in the iterations.

[andriimaryskevych]

We faced the same issue with this library. @ForbesLindesay please take a look at this - the library has a critical bug and it has 18m+ weekly downloads

[peterlundberg]

Can confirm and isolate this a bit more also without the chunking above.

And yes the blocksize is the magic number 64 https://github.com/ForbesLindesay/throat/blob/master/index.js#L105

async function demoExitBug() {
  const limitedConcurrency = throat(1);
  for (let i = 0; i < 100; i += 1) {
    console.log('working on', i);
    await Promise.all([
      limitedConcurrency(async () => true), // with just one it would complete
      limitedConcurrency(async () => true), // concurrency + 1 = only 64 ok
      // limitedConcurrency(async () => true), // concurrency + 2 = only 32 ok
    ]);
  }
  console.log('Done!'); // This will not be reached in 6.0.1
}
demoExitBug();

Looks like this was introduced in 6.0.1 8fd7a02#diff-e727e4bdf3657fd1d798edcd6b099d6e092f8573cba266154583a746bba0f346R123

[ForbesLindesay]

Sorry, didn't notice the issue. Pinging me on twitter is often good for super high priority issues like this. I'll push out a fix shortly.

[ForbesLindesay]

This is resolved in v6.0.2