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// Copyright 2022 The Pigweed Authors
//
// Licensed under the Apache License, Version 2.0 (the "License"); you may not
// use this file except in compliance with the License. You may obtain a copy of
// the License at
//
// https://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
// License for the specific language governing permissions and limitations under
// the License.
/**
* Provides a simple array-based queue that will block caller on await
* queue.shift() if the queue is empty, until a new item is pushed to the
* queue. */
export default class Queue<T> {
queue = Array<T>();
elementListeners = Array<() => void>();
get length(): number {
return this.queue.length;
}
push(...items: T[]): number {
this.queue.push(...items);
this._checkListeners();
return this.length;
}
shift(): Promise<T> {
return new Promise(resolve => {
if (this.length > 0) {
return resolve(this.queue.shift()!);
} else {
this.elementListeners.push(() => {
return resolve(this.queue.shift()!);
});
}
});
}
_checkListeners() {
if (this.length > 0 && this.elementListeners.length > 0) {
const listener = this.elementListeners.shift()!;
listener.call(this);
this._checkListeners();
}
}
unshift(...items: T[]): number {
this.queue.unshift(...items);
this._checkListeners();
return this.length;
}
}
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