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import { E_CANCELED } from './errors';
import type { SemaphoreInterface } from './semaphoreinterface';
interface Priority {
priority: number;
}
interface QueueEntry {
resolve(result: [number, SemaphoreInterface.Releaser]): void;
reject(error: unknown): void;
weight: number;
priority: number;
}
interface Waiter {
resolve(): void;
priority: number;
}
class Semaphore implements SemaphoreInterface {
constructor(
private _value: number,
private _cancelError: Error = E_CANCELED
) {}
acquire(
weight = 1,
priority = 0
): Promise<[number, SemaphoreInterface.Releaser]> {
if (weight <= 0)
throw new Error(`invalid weight ${weight}: must be positive`);
return new Promise((resolve, reject) => {
const task: QueueEntry = { resolve, reject, weight, priority };
const i = findIndexFromEnd(
this._queue,
(other) => priority <= other.priority
);
if (i === -1 && weight <= this._value) {
// Needs immediate dispatch, skip the queue
this._dispatchItem(task);
} else {
this._queue.splice(i + 1, 0, task);
}
});
}
async runExclusive<T>(
callback: SemaphoreInterface.Worker<T>,
weight = 1,
priority = 0
): Promise<T> {
const [value, release] = await this.acquire(weight, priority);
try {
return await callback(value);
} finally {
release();
}
}
waitForUnlock(weight = 1, priority = 0): Promise<void> {
if (weight <= 0)
throw new Error(`invalid weight ${weight}: must be positive`);
if (this._couldLockImmediately(weight, priority)) {
return Promise.resolve();
} else {
return new Promise((resolve) => {
if (!this._weightedWaiters[weight - 1])
this._weightedWaiters[weight - 1] = [];
insertSorted(this._weightedWaiters[weight - 1], { resolve, priority });
});
}
}
isLocked(): boolean {
return this._value <= 0;
}
getValue(): number {
return this._value;
}
setValue(value: number): void {
this._value = value;
this._dispatchQueue();
}
release(weight = 1): void {
if (weight <= 0)
throw new Error(`invalid weight ${weight}: must be positive`);
this._value += weight;
this._dispatchQueue();
}
cancel(): void {
this._queue.forEach((entry) => entry.reject(this._cancelError));
this._queue = [];
}
private _dispatchQueue(): void {
this._drainUnlockWaiters();
while (this._queue.length > 0 && this._queue[0].weight <= this._value) {
this._dispatchItem(this._queue.shift()!);
this._drainUnlockWaiters();
}
}
private _dispatchItem(item: QueueEntry): void {
const previousValue = this._value;
this._value -= item.weight;
item.resolve([previousValue, this._newReleaser(item.weight)]);
}
private _newReleaser(weight: number): () => void {
let called = false;
return () => {
if (called) return;
called = true;
this.release(weight);
};
}
private _drainUnlockWaiters(): void {
if (this._queue.length === 0) {
for (let weight = this._value; weight > 0; weight--) {
const waiters = this._weightedWaiters[weight - 1];
if (!waiters) continue;
waiters.forEach((waiter) => waiter.resolve());
this._weightedWaiters[weight - 1] = [];
}
} else {
const queuedPriority = this._queue[0].priority;
for (let weight = this._value; weight > 0; weight--) {
const waiters = this._weightedWaiters[weight - 1];
if (!waiters) continue;
const i = waiters.findIndex(
(waiter) => waiter.priority <= queuedPriority
);
(i === -1 ? waiters : waiters.splice(0, i)).forEach((waiter) =>
waiter.resolve()
);
}
}
}
private _couldLockImmediately(weight: number, priority: number) {
return (
(this._queue.length === 0 || this._queue[0].priority < priority) &&
weight <= this._value
);
}
private _queue: Array<QueueEntry> = [];
private _weightedWaiters: Array<Array<Waiter>> = [];
}
function insertSorted<T extends Priority>(a: T[], v: T) {
const i = findIndexFromEnd(a, (other) => v.priority <= other.priority);
a.splice(i + 1, 0, v);
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