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pool.ts
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pool.ts
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/*!
* Copyright 2018 Google Inc. All Rights Reserved.
*
* 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
*
* http://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.
*/
import * as assert from 'assert';
import {logger} from './logger';
/**
* An auto-resizing pool that distributes concurrent operations over multiple
* clients of type `T`.
*
* ClientPool is used within Firestore to manage a pool of GAPIC clients and
* automatically initializes multiple clients if we issue more than 100
* concurrent operations.
*
* @private
*/
export class ClientPool<T> {
/**
* Stores each active clients and how many operations it has outstanding.
* @private
*/
private activeClients: Map<T, number> = new Map();
/**
* @param concurrentOperationLimit The number of operations that each client
* can handle.
* @param clientFactory A factory function called as needed when new clients
* are required.
*/
constructor(
private readonly concurrentOperationLimit: number,
private readonly clientFactory: () => T
) {}
/**
* Returns an already existing client if it has less than the maximum number
* of concurrent operations or initializes and returns a new client.
*
* @private
*/
private acquire(requestTag: string): T {
let selectedClient: T | null = null;
let selectedRequestCount = 0;
this.activeClients.forEach((requestCount, client) => {
if (!selectedClient && requestCount < this.concurrentOperationLimit) {
logger(
'ClientPool.acquire',
requestTag,
'Re-using existing client with %s remaining operations',
this.concurrentOperationLimit - requestCount
);
selectedClient = client;
selectedRequestCount = requestCount;
}
});
if (!selectedClient) {
logger('ClientPool.acquire', requestTag, 'Creating a new client');
selectedClient = this.clientFactory();
assert(
!this.activeClients.has(selectedClient),
'The provided client factory returned an existing instance'
);
}
this.activeClients.set(selectedClient, selectedRequestCount + 1);
return selectedClient!;
}
/**
* Reduces the number of operations for the provided client, potentially
* removing it from the pool of active clients.
* @private
*/
private release(requestTag: string, client: T): void {
let requestCount = this.activeClients.get(client) || 0;
assert(requestCount > 0, 'No active request');
requestCount = requestCount! - 1;
this.activeClients.set(client, requestCount);
if (requestCount === 0) {
const deletedCount = this.garbageCollect();
if (deletedCount) {
logger(
'ClientPool.release',
requestTag,
'Garbage collected %s clients',
deletedCount
);
}
}
}
/**
* The number of currently registered clients.
*
* @return Number of currently registered clients.
* @private
*/
// Visible for testing.
get size(): number {
return this.activeClients.size;
}
/**
* The number of currently active operations.
*
* @return Number of currently active operations.
* @private
*/
// Visible for testing.
get opCount(): number {
let activeOperationCount = 0;
this.activeClients.forEach(count => (activeOperationCount += count));
return activeOperationCount;
}
/**
* Runs the provided operation in this pool. This function may create an
* additional client if all existing clients already operate at the concurrent
* operation limit.
*
* @param requestTag A unique client-assigned identifier for this operation.
* @param op A callback function that returns a Promise. The client T will
* be returned to the pool when callback finishes.
* @return A Promise that resolves with the result of `op`.
* @private
*/
run<V>(requestTag: string, op: (client: T) => Promise<V>): Promise<V> {
const client = this.acquire(requestTag);
return op(client)
.catch(err => {
this.release(requestTag, client);
return Promise.reject(err);
})
.then(res => {
this.release(requestTag, client);
return res;
});
}
/**
* Deletes clients that are no longer executing operations. Keeps up to one
* idle client to reduce future initialization costs.
*
* @return Number of clients deleted.
* @private
*/
private garbageCollect(): number {
let idleClients = 0;
this.activeClients.forEach((requestCount, client) => {
if (requestCount === 0) {
++idleClients;
if (idleClients > 1) {
this.activeClients.delete(client);
}
}
});
return idleClients - 1;
}
}