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initial attempt at pulling retries into qdone
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,111 @@ | ||
| /** | ||
| * Exponential backoff controller. | ||
| * usage: | ||
| * const exp = new ExponentialBackoff() | ||
| * const result = await exp.run( | ||
| * function action (attemptNumber) { | ||
| * console.log(attemptNumber) // 1, 2, 3, ... | ||
| * return axios.post(...) | ||
| * }, | ||
| * function shouldRetry (returnValue, error) { | ||
| * if (returnValue && return value.code = 500) return true | ||
| * if (error && error.message === 'Internal Server Error') return true | ||
| * } | ||
| * ) | ||
| */ | ||
|
|
||
| export class ExponentialBackoff { | ||
| /** | ||
| * Creates various behaviors for backoff. | ||
| * @param {number} maxRetries - Number of times to attempt the action before | ||
| * throwing an error. Defaults to 3. | ||
| * @param {number} maxJitterPercent - Jitter as a percentage of the delay. | ||
| * For example, if the exponential delay is 2 seconds, then a jitter of | ||
| * 0.5 could lead to a delay as low as 1 second and as high as 3 seconds, | ||
| * since 0.5 * 2 = 1. Defaults to 0.5. | ||
| * @param {number} exponentBase - The base for the exponent. Defaults to 2, | ||
| * which means the delay doubles every attempt. | ||
| */ | ||
| constructor (maxRetries = 3, maxJitterPercent = 0.5, exponentBase = 2) { | ||
| if (maxRetries < 1) throw new Error('maxRetries must be >= 1') | ||
| if (maxJitterPercent < 0.1 || maxJitterPercent > 1) throw new Error('maxJitterPercent must be in the interval [0.1, 1]') | ||
| if (exponentBase < 1 || exponentBase > 10) throw new Error('exponentBase must be in the range [1, 10]') | ||
| this.maxRetries = parseInt(maxRetries) | ||
| this.maxJitterPercent = parseFloat(maxJitterPercent) | ||
| this.exponentBase = parseFloat(exponentBase) | ||
| this.attemptNumber = 0 | ||
| } | ||
|
|
||
| /** | ||
| * Calculates how many ms to delay based on the current attempt number. | ||
| */ | ||
| calculateDelayMs (attemptNumber) { | ||
| const secondsRaw = this.exponentBase ** attemptNumber // 2, 4, 8, 16, .... | ||
| const jitter = this.maxJitterPercent * (Math.random() - 0.5) // [-0.5, 0.5] | ||
| const delayMs = Math.round(secondsRaw * (1 + jitter) * 1000) | ||
| // console.log({ secondsRaw, jitter, delayMs }) | ||
| return delayMs | ||
| } | ||
|
|
||
| /** | ||
| * Resolves after a delay set by the current attempt. | ||
| */ | ||
| async delay (attemptNumber) { | ||
| // console.log(attemptNumber) | ||
| const delay = this.calculateDelayMs(attemptNumber) | ||
| // console.log({ function: 'delay', attemptNumber, delay }) | ||
| return new Promise((resolve, reject) => setTimeout(resolve, delay)) | ||
| } | ||
|
|
||
| /** | ||
| * Call another function repeatedly, retrying with exponential backoff and | ||
| * jitter if not successful. | ||
| * @param {ExponentialBackoff~action} action - Callback that does the action | ||
| * to be attempted (web request, rpc, database call, etc). Will be called | ||
| * again after the exponential dealy if shouldRetry() returns true. | ||
| * @param {ExponentialBackoff~shouldRetry} shouldRetry - Callback that gets | ||
| * to look at the return value of action() and any potential exception. If | ||
| * this returns true then the action will be retried with the appropriate | ||
| * backoff delay. Defaults to a function that returns true if an exception | ||
| * is thrown. | ||
| */ | ||
| async run ( | ||
| action = async (attemptNumber) => undefined, | ||
| shouldRetry = async (returnValue, error) => !!error | ||
| ) { | ||
| let attemptNumber = 0 | ||
| while (attemptNumber++ < this.maxRetries) { | ||
| try { | ||
| const result = await action(attemptNumber) | ||
| if (await shouldRetry(result, undefined)) { | ||
| if (attemptNumber >= this.maxRetries) throw new Error('Maximum number of attempts reached') | ||
| await this.delay(attemptNumber) | ||
| } else { | ||
| return result | ||
| } | ||
| } catch (e) { | ||
| if (await shouldRetry(undefined, e)) { | ||
| if (attemptNumber >= this.maxRetries) throw e | ||
| await this.delay(attemptNumber) | ||
| } else { | ||
| throw e | ||
| } | ||
| } | ||
| } | ||
| } | ||
|
|
||
| /** | ||
| * Callback used by run(). | ||
| * @callback ExponentialBackoff~action | ||
| * @param {number} attemptNumber - Which attempt this is, i.e. 1, 2, 3, ... | ||
| */ | ||
|
|
||
| /** | ||
| * Callback used by run(). | ||
| * @callback ExponentialBackoff~shouldRetry | ||
| * @param returnValue - The value returned by your action. If an exception | ||
| * was thrown by the action then this is undefined. | ||
| * @param error - The exception thrown by your action. If there was no | ||
| * exception, this is undefined. | ||
| */ | ||
| } |
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