Class AsyncLock

Not providing a key to the methods makes this function as if it were a normal Semaphore.

example

const lock = new AsyncLock();

async function write(text: string, key: string, delay?: number): Promise<void> {
     await lock.withLock(async () => {
         // wait 500ms
         await new Promise(res => setTimeout(res, 500 + (delay || 0)));
         console.info(text);
     }, key);
}

// these operations will practically start at the same time!
// but there will be a 500ms delay between write calls of the same key

write("this", "a");
write("is", "a");
write("me", "a", 10);

write("cute", "b");
write("not", "b");
write("loyal", "b");

write("dog", "c");
write("very", "c");
write("to", "c");

// Output:
// *500ms pass*
// this cute dog
// *500ms pass*
// is not very
// *500ms pass*
// loyal to me