1 files changed, 176 insertions, 0 deletions
diff --git a/src/lib/vendor/async-mutex/semaphore.ts b/src/lib/vendor/async-mutex/semaphore.ts
new file mode 100644
index 0000000..385e814
--- /dev/null
+++ b/src/lib/vendor/async-mutex/semaphore.ts
@@ -0,0 +1,176 @@
+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);
+}
+
+function findIndexFromEnd<T>(a: T[], predicate: (e: T) => boolean): number {
+  for (let i = a.length - 1; i >= 0; i--) {
+    if (predicate(a[i])) {
+      return i;
+    }
+  }
+  return -1;
+}
+
+export default Semaphore;