前言
最近两天的 web 前端开发中,早前的锁实现 (自旋锁) 出现了一些不合理的现象,所以有了这片随笔
什么是协程锁?能点进这个博客的的你肯定是明白的,不明白的人根本搜不到我这随笔,不多做赘述。
一些个人认识和实现经验
暂时想到这么多,欢迎补充。
设计
实现
// Synchronized async function const NEXT = Symbol(); const PREV = Symbol(); type LevelsNode = { [NEXT]?: LevelsMap; pendings?: PendingPromise<any>[]; [PREV]?: LevelsNode; key: string }; type LevelsMap = Map<any, LevelsNode>; function findSyncNode(syncMap: LevelsMap, keys: any[], creation: false): [LevelsMap | undefined, LevelsNode | undefined, PendingPromise<any>[] | undefined]; function findSyncNode(syncMap: LevelsMap, keys: any[], creation: true): [LevelsMap, LevelsNode, PendingPromise<any>[]]; function findSyncNode(syncMap: LevelsMap, keys: any[], creation: boolean) { let prntNode: LevelsNode | undefined; let map: LevelsMap | undefined = syncMap; for (let i = 0; !!map && i < keys.length - 1; i++) { let lastNode = prntNode; prntNode = map.get(keys[i]); if (!prntNode) { if (creation) { prntNode = { [NEXT]: new Map(), [PREV]: lastNode, key: keys[i] }; map.set(keys[i], prntNode); map = prntNode[NEXT]; } else { map = undefined; } } else if (!(map = prntNode[NEXT])) { if (creation) { prntNode[NEXT] = new Map(); map = prntNode[NEXT]; } else { if (i < keys.length - 2) prntNode = undefined; } } } let mapNode = map?.get(keys[keys.length - 1]); if (creation) { if (!map) { Throwable("Impossible Error: No Prev Map."); } else if (!mapNode) { map.set(keys[keys.length - 1], (mapNode = { pendings: [], [PREV]: prntNode, key: keys[keys.length - 1] })); } else if (!mapNode.pendings) { mapNode.pendings = []; } } return [map, mapNode, mapNode?.pendings]; } const getPendings = (syncMap: LevelsMap, keys: any[]) => findSyncNode(syncMap, keys, false)[2]; const addPendings = (syncMap: LevelsMap, keys: any[]) => findSyncNode(syncMap, keys, true)[2]; const delPendings = (syncMap: LevelsMap, keys: any[]) => { const [finalMap, finalVal] = findSyncNode(syncMap, keys, false); if (!!finalMap && !!finalVal) { // delete pending delete finalVal.pendings; // delete above including self tryDeleteNodeAndAbove(syncMap, finalVal); } }; const tryDeleteNodeAndAbove = (syncMap: LevelsMap, node?: LevelsNode) => { while (!!node) { const nextMap = node[NEXT]; if (!node.pendings && (!nextMap || nextMap.size === 0)) { const nodeKey = node.key; node = node[PREV]; const map = node?.[NEXT] || syncMap; map.delete(nodeKey); } else { break; } } };
const asyncOneMap: LevelsMap = new Map<any, LevelsNode>(); export const asyncOne = async <T>(call: () => Promise<T>, ...keys: any[]): Promise<T> => { let pendings = getPendings(asyncOneMap, keys); if (!!pendings) { return (pendings[pendings.length] = pendingResolve<T>()); } else { pendings = addPendings(asyncOneMap, keys); try { const result = await call.call(null); pendings.forEach(p => setTimeout(() => p.resolve(result))); return result; } catch (e) { pendings.forEach(p => setTimeout(() => p.reject(e))); throw e; } finally { delPendings(asyncOneMap, keys); } } };
const asyncWaitMap: LevelsMap = new Map<any, LevelsNode>(); export const asyncWait = async <T>(call: () => Promise<T>, ...keys: any[]) => { let pendings = getPendings(asyncWaitMap, keys); /*sleep*/ if (!!pendings) await (pendings[pendings.length] = pendingResolve<void>()); /*continue-------------*/ else pendings = addPendings(asyncWaitMap, keys); try { return await call.call(null); } finally { const next4awaken = pendings.shift(); /*awaken the next*/ if (next4awaken !== undefined) next4awaken.resolve(); /*unlock-----------------------------------*/ else delPendings(asyncWaitMap, keys); } };