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export type SemElement = [string, (value: any | PromiseLike<any>) => void];
/**
* A semaphore implementation that limits the number of concurrent operations.
* <p>
* The semaphore maintains an internal queue of pending requests and a set of
* active tokens. When the number of active tokens is below the configured
* maximum, the next request in the queue is granted immediately. Each granted
* request receives a release callback; calling this callback frees a token
* and triggers the next pending request.
* <p>
* Internally the semaphore tracks active tokens in a {@link Map} and pending
* requests in an array. The {@link request} method returns a {@link Promise}
* that resolves to a release function. The release function removes the
* token from the active set and potentially starts the next pending request.
* <p>
* The semaphore is thread‑safe with respect to the event loop, as all state
* mutations occur synchronously within the call stack of the {@link request}
* and {@link release} methods.
*
* @param {number} [max=1] - The maximum number of concurrent operations allowed.
*/
export class CoreSemaphor {
private curQueue: Map<string, SemElement>;
private readonly max: number;
private callbackQueue: SemElement[];
constructor(max = 1) {
this.curQueue = new Map();
this.callbackQueue = [];
this.max = max;
this.release = this.release.bind(this);
}
hasFree() {
return this.curQueue.size < this.max;
}
async request(): Promise<() => void> {
const uuid = crypto.randomUUID();
return new Promise((resolve) => {
this.callbackQueue.push([uuid, resolve]);
this.startNext();
});
}
private startNext() {
if (this.hasFree()) {
const el = this.callbackQueue.shift();
if (el) {
const [uuid, resolve] = el;
this.curQueue.set(uuid, el);
resolve(() => {
this.release(uuid);
});
this.startNext();
}
}
}
private release(uuid: string) {
Eif (this.curQueue.has(uuid)) {
this.curQueue.delete(uuid);
}
this.startNext();
}
}
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