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|
import { Mutex, type MutexInterface } from './async-mutex';
export interface RWLockInterface {
readonly readerCount: number;
readonly writerCount: number;
acquireRead(priority?: number): Promise<() => void>;
acquireWrite(priority?: number): Promise<() => void>;
withRead<T>(f: () => Promise<T>): Promise<T>;
withWrite<T>(f: () => Promise<T>): Promise<T>;
isLocked(): boolean;
waitForUnlock(priority?: number): Promise<void>;
}
/** RWLock Helper Methods + Base Interface */
export abstract class RWLockAbstract implements RWLockInterface {
protected abstract _readerCount: number;
protected abstract _writerCount: number;
public get readerCount(): number {
return this._readerCount;
}
public get writerCount(): number {
return this._writerCount;
}
public abstract acquireRead(priority?: number): Promise<() => void>;
public abstract acquireWrite(priority?: number): Promise<() => void>;
public async withRead<T>(f: () => Promise<T>): Promise<T> {
const release = await this.acquireRead();
try {
return await f();
} finally {
release();
}
}
public async withWrite<T>(f: () => Promise<T>): Promise<T> {
const release = await this.acquireWrite();
try {
return await f();
} finally {
release();
}
}
public abstract isLocked(): boolean;
public abstract waitForUnlock(priority?: number): Promise<void>;
}
/**
* Single threaded read write lock
*
* Based on https://gist.github.com/CMCDragonkai/4de5c1526fc58dac259e321db8cf5331
*/
export class RWLockImpl extends RWLockAbstract {
protected _readerCount: number = 0;
protected _writerCount: number = 0;
protected lock: Mutex = new Mutex();
protected release?: MutexInterface.Releaser;
public async acquireRead(priority?: number): Promise<() => void> {
const readerCount = ++this._readerCount;
// The first reader locks
if (readerCount === 1) {
this.release = await this.lock.acquire(priority);
}
return () => {
const readerCount = --this._readerCount;
// The last reader unlocks
if (readerCount === 0) {
if (!this.release)
throw new ReferenceError('this.release is undefined');
this.release();
}
};
}
public async acquireWrite(priority?: number): Promise<() => void> {
++this._writerCount;
this.release = await this.lock.acquire(priority);
return () => {
--this._writerCount;
if (!this.release) throw new ReferenceError('this.release is undefined');
this.release();
};
}
public isLocked(): boolean {
return this.lock.isLocked();
}
public async waitForUnlock(priority?: number): Promise<void> {
return this.lock.waitForUnlock(priority);
}
}
export type RWLock = RWLockAbstract;
export const RWLock = RWLockImpl;
/**
* Joined RWLock - Joins multiple {@link RWLock}s, allowing them to be used as one; read locking will read lock all children, write locking will write lock all children.
* Note: Locking increments readerCount and writerCount by however many locks are in the join
*/
export class JoinedRWLock extends RWLockAbstract {
public constructor(...childLocks: RWLockAbstract[]) {
super();
this._children = childLocks;
}
protected _children: RWLockAbstract[];
protected get _readerCount() {
return this._children
.map((v) => v['_readerCount'])
.reduce((pv, cv) => pv + cv, 0);
}
protected get _writerCount() {
return this._children
.map((v) => v['_writerCount'])
.reduce((pv, cv) => pv + cv, 0);
}
/**
* Helper for acquireRead and acquireWrite
* @param priority Priority passed to acquire
* @param greedy If we should attempt to get the underlying locks whilst waiting on others. This gives us priority, but may make other operations take forever. `-1`=Never be greedy, `0`=Immediately be greedy, `>0`=Wait `greedyAfter` seconds before being greedy (leaks a Promise if timeout reached)
*/
private async acquireGeneric(
acquire: (lock: RWLock, priority?: number) => Promise<() => void>,
priority?: number,
greedyAfter = -1
) {
if (greedyAfter === -1) await this.waitForUnlock(priority);
else if (greedyAfter !== 0)
await Promise.race([
this.waitForUnlock(priority),
new Promise((rs) => setTimeout(rs, greedyAfter * 1000)),
]);
else {
// being greedy immediately, just aquire locks now
}
const _locks = await Promise.allSettled(
this._children.map((v) => acquire(v))
);
const errs = [] as unknown[];
const locks = _locks.map((v) => {
if (v.status === 'rejected') {
errs.push(v.reason);
return null as never;
} else {
return v.value;
}
});
if (errs.length) {
let unlockErrs: unknown[] =
|
