p-lock
v3.0.0
Published
Simple promise lock
Downloads
27,100
Readme
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About
This package provides a simple promise lock, which is useful for preventing race conditions between multiple promises.
Installation
yarn add p-lock
npm install p-lock
pnpm install p-lock
Overview
First, we get a lock function:
import { getLock } from "p-lock";
const lock = getLock();
Calling the lock function returns a promise that resolves when the lock is acquired.
The promise resolves with a release function, which must be called to release the lock:
lock("example-key").then((release) => {
// Now I have the lock for "example-key"
// do something...
release();
});
Full Example
In this example, we have two promises writing to the same file. However, we want to ensure that the first one finishes before the second one starts.
import { writeFile } from "fs";
import { getLock } from "p-lock";
const lock = getLock();
lock("file").then((release) => {
setTimeout(() => {
writeFile("test.txt", "hello", () => {
release();
});
}, 1000);
});
lock("file").then((release) => {
writeFile("test.txt", "world", () => {
release();
});
});
// Contents of test.txt will be "world"
Replace
In some cases, we may want to replace an existing promise waiting for a lock, rather than waiting for it to finish.
The replace
option allows us to do this:
import { writeFile } from "fs";
import { getLock } from "p-lock";
const lock = getLock({ replace: true });
let writeCounter = 0;
lock("file").then((release) => {
setTimeout(() => {
writeCounter += 1;
writeFile("test.txt", `update #${writeCounter}`, () => {
release();
});
}, 1000);
});
lock("file").then((release) => {
writeCounter += 1;
writeFile("test.txt", `update #${writeCounter}`, () => {
release();
});
}).catch(() => {
// This promise will reject, since the next one replaces.
});
lock("file").then((release) => {
writeCounter += 1;
writeFile("test.txt", `update #${writeCounter}`, () => {
release();
});
});
// Contents of test.txt will be "update #2"
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MIT - MIT License