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joplin/packages/lib/InMemoryCache.ts

85 lines
2.1 KiB
TypeScript

// There are plenty of packages for in-memory caching but each have their
// own gotchas and often have extra complexity which makes it work in one
// platform but not in another (for example, the use of long timeouts would
// be fine in Node but not in React Native).
//
// So this class implements a simple in-memory cache with support for TTL.
// Checking for expired keys is a bit inefficient since it doesn't rely on
// timers, so it's checking every time a value is set or retrieved. But it
// should be fine in most cases, as long as the class is not used at a massive
// scale.
interface Record {
value: any;
expiredTime: number;
}
interface Records {
[key: string]: Record;
}
interface ExpirableKeys {
[key: string]: boolean;
}
export default class Cache {
private maxRecords_: number;
private records_: Records = {};
private expirableKeys_: ExpirableKeys = {};
private recordKeyHistory_: string[] = [];
constructor(maxRecords: number = 50) {
this.maxRecords_ = maxRecords;
}
private checkExpiredRecords() {
const now = Date.now();
for (const key in this.expirableKeys_) {
if (!this.records_[key]) {
delete this.expirableKeys_[key];
} else {
if (this.records_[key].expiredTime <= now) {
delete this.records_[key];
delete this.expirableKeys_[key];
}
}
}
while (this.recordKeyHistory_.length > this.maxRecords_) {
const key = this.recordKeyHistory_[0];
delete this.records_[key];
delete this.expirableKeys_[key];
this.recordKeyHistory_.splice(0, 1);
}
}
public value(key: string, defaultValue: any = undefined): any {
this.checkExpiredRecords();
if (key in this.records_) return this.records_[key].value;
return defaultValue;
}
public setValue(key: string, value: any, ttl: number = 0) {
this.checkExpiredRecords();
this.records_[key] = {
value: value,
expiredTime: ttl ? Date.now() + ttl : 0,
};
const idx = this.recordKeyHistory_.indexOf(key);
if (idx >= 0) this.recordKeyHistory_.splice(idx, 1);
this.recordKeyHistory_.push(key);
if (ttl) {
this.expirableKeys_[key] = true;
} else {
delete this.expirableKeys_[key];
}
}
}