A reader-writer lock implementation that allows multiple concurrent reads but only one write at a time. Readers can acquire the lock simultaneously as long as there are no writers holding the lock. Writers block all other readers and writers until the write operation completes.

import { AsyncValue } from "https://deno.land/x/async@v2.1.0/testutil.ts";
import { RwLock } from "https://deno.land/x/async@v2.1.0/rw_lock.ts";

const count = new RwLock(new AsyncValue(0));

// rlock should allow multiple readers at a time
await Promise.all([...Array(10)].map(() => {
  return count.rlock(async (count) => {
    console.log(await count.get());
  });
}));

// lock should allow only one writer at a time
await Promise.all([...Array(10)].map(() => {
  return count.lock(async (count) => {
    const v = await count.get();
    console.log(v);
    count.set(v + 1);
  });
}));