semaphore.ts
| 1 | type PromiseResolver = () => void; |
| 2 | |
| 3 | export class AsyncSemaphore { |
| 4 | private maxConcurrency: number; |
| 5 | private running: number; |
| 6 | private waitQueue: PromiseResolver[]; |
| 7 | |
| 8 | /** |
| 9 | * Creates a new AsyncSemaphore. |
| 10 | * @param maxConcurrency The maximum number of concurrent executions allowed. Must be a positive integer. |
| 11 | */ |
| 12 | constructor(maxConcurrency: number) { |
| 13 | if (typeof maxConcurrency !== "number" || !Number.isInteger(maxConcurrency) || maxConcurrency <= 0) { |
| 14 | throw new Error("AsyncSemaphore: maxConcurrency must be a positive integer."); |
| 15 | } |
| 16 | this.maxConcurrency = maxConcurrency; |
| 17 | this.running = 0; |
| 18 | this.waitQueue = []; |
| 19 | } |
| 20 | |
| 21 | setMaxConcurrency(newMax: number): void { |
| 22 | this.maxConcurrency = newMax; |
| 23 | } |
| 24 | |
| 25 | async acquire(): Promise<void> { |
| 26 | if (this.running < this.maxConcurrency) { |
| 27 | // slot acquired immediately |
| 28 | this.running++; |
| 29 | return Promise.resolve(); |
| 30 | } |
| 31 | |
| 32 | // No slots available, wait in the queue |
| 33 | return new Promise<void>((resolve) => { |
| 34 | this.waitQueue.push(resolve); |
| 35 | }); |
| 36 | } |
| 37 | |
| 38 | release(): void { |
| 39 | // If there are waiters, and we still have concurrency left (might have changed), wake one up |
| 40 | if (this.waitQueue.length > 0 && this.running <= this.maxConcurrency) { |
| 41 | const nextResolver = this.waitQueue.shift(); |
| 42 | if (nextResolver) { |
| 43 | // Defer resolution to avoid potential deep stacks |
| 44 | // and allow the current execution context to complete. |
| 45 | queueMicrotask(nextResolver); |
| 46 | } |
| 47 | } else if (this.running > 0) { |
| 48 | this.running--; |
| 49 | } |
| 50 | } |
| 51 | } |
| 52 |