promise-critical-section

Allows only one asynchronous operation to run every time.

Although JavaScript is single-threaded, there are times you may want to limit number of asynchronous operation to enter a block simultaneously. For example,

• Pooling a single resource
• Running a series of asynchronous steps one-by-one

How to use

In the code below, Step 1A and Step 1B will be run serially regardless of race condition from Step 2.

import CriticalSection from 'promise-critical-section';

const section = new CriticalSection();

Promise.race([
  section.enter()
    .then(() => {
      // do something that is limited to one asynchoronous operation
      console.log('Step 1A');
    })
    .then(() => {
      // do another thing
      console.log('Step 1B');
    })
    .then(() => section.leave()),
  section.enter()
    .then(() => {
      // do something in the critical section
      console.log('Step 2');
    })
    .then(() => section.leave())
])

You can also write it with ES7 async/await. The following example maybe a bit exaggerated.

return Promise.all([
  (async () => {
    await section.enter();
    console.log('Step 1A');
    console.log('Step 1B');
    await section.leave();
  })(),
  (async () => {
    await section.enter();
    console.log('Step 2');
    await section.leave();
  })()
]);

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