deno.land / x / replicache@v10.0.0-beta.0 / connection-loop.ts
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export const DEBOUNCE_DELAY_MS = 10;
export const MIN_DELAY_MS = 30;export const MAX_DELAY_MS = 60_000;
type SendRecord = {duration: number; ok: boolean};
export interface ConnectionLoopDelegate extends OptionalLogger { invokeSend(): Promise<boolean>; debounceDelay: number; // If null, no watchdog timer is used. watchdogTimer: number | null; maxConnections: number; maxDelayMs: number; minDelayMs: number;}
export class ConnectionLoop { // ConnectionLoop runs a loop sending network requests (either pushes or // pulls) to the server. Our goal, generally, is to send requests as fast as // we can, but to adjust in case of slowness, network errors, etc. We will // send requests in parallel if the server supports it. We also debounce // pushes since they frequently happen in series very near to one another // (e.g., during drag'n drops). // // The loop flows through the following states forever, until it is closed: // // Pending: Wait for event or watchdog // | // v // Debounce: Wait for more events (we debounce pushes) // | // v // Wait for available connection (we limit number of parallel requests // allowed) // | // v // Wait to send (if requests are taking too long, we will slow down) // | // v // Send (asynchronously, wrt the loop) // | // v // Back to the pending!
// Controls whether the next iteration of the loop will wait at the pending // state. private _pendingResolver = resolver<void>();
private readonly _delegate: ConnectionLoopDelegate; private _closed = false;
constructor(delegate: ConnectionLoopDelegate) { this._delegate = delegate; // eslint-disable-next-line @typescript-eslint/no-floating-promises this.run(); }
close(): void { this._closed = true; }
send(): void { this._delegate.debug?.('send'); this._pendingResolver.resolve(); }
async run(): Promise<void> { const sendRecords: SendRecord[] = [];
let recoverResolver = resolver(); let lastSendTime;
// The number of active connections. let counter = 0; const delegate = this._delegate; const {debug} = delegate; let delay = 0;
debug?.('Starting connection loop');
while (!this._closed) { debug?.( didLastSendRequestFail(sendRecords) ? 'Last request failed. Trying again' : 'Waiting for a send', );
// Wait until send is called or until the watchdog timer fires. const races = [this._pendingResolver.promise]; const t = delegate.watchdogTimer; if (t !== null) { races.push(sleep(t)); } await Promise.race(races); if (this._closed) break;
debug?.('Waiting for debounce'); await sleep(delegate.debounceDelay); if (this._closed) break; debug?.('debounced');
// This resolver is used to wait for incoming push calls. this._pendingResolver = resolver();
if (counter >= delegate.maxConnections) { debug?.('Too many request in flight. Waiting until one finishes...'); await this._waitUntilAvailableConnection(); if (this._closed) break; debug?.('...finished'); }
// We need to delay the next request even if there are no active requests // in case of error. if (counter > 0 || didLastSendRequestFail(sendRecords)) { delay = computeDelayAndUpdateDurations(delay, delegate, sendRecords); debug?.( didLastSendRequestFail(sendRecords) ? 'Last connection errored. Sleeping for' : 'More than one outstanding connection (' + counter + '). Sleeping for', delay, 'ms', ); } else { // We set this to 0 here in case minDelayMs is mutated to a lower value // than the old delay so that we still get minDelayMs. This can happen // if we get an error during a run where minDelayMs is larger than the // current value of minDelayMs. delay = 0; }
const clampedDelay = Math.min( delegate.maxDelayMs, Math.max(delegate.minDelayMs, delay), ); if (lastSendTime !== undefined) { const timeSinceLastSend = Date.now() - lastSendTime; if (clampedDelay > timeSinceLastSend) { await Promise.race([ sleep(clampedDelay - timeSinceLastSend), recoverResolver.promise, ]); if (this._closed) break; } }
counter++; // eslint-disable-next-line @typescript-eslint/no-floating-promises (async () => { const start = Date.now(); let ok: boolean; try { lastSendTime = start; debug?.('Sending request'); ok = await delegate.invokeSend(); debug?.('Send returned', ok); } catch (e) { debug?.('Send failed', e); ok = false; } if (this._closed) { debug?.('Closed after invokeSend'); return; } debug?.('Request done', {duration: Date.now() - start, ok}); sendRecords.push({duration: Date.now() - start, ok}); if (recovered(sendRecords)) { recoverResolver.resolve(); recoverResolver = resolver(); } counter--; this._connectionAvailable(); if (!ok) { // Keep trying this._pendingResolver.resolve(); } })(); } }
private _waitingConnectionResolve: (() => void) | undefined = undefined;
private _connectionAvailable() { if (this._waitingConnectionResolve) { const resolve = this._waitingConnectionResolve; this._waitingConnectionResolve = undefined; resolve(); } }
private _waitUntilAvailableConnection() { const {promise, resolve} = resolver(); this._waitingConnectionResolve = resolve; return promise; }}
// Number of connections to remember when computing the new delay.const CONNECTION_MEMORY_COUNT = 9;
// Computes a new delay based on the previous requests. We use the median of the// previous successfull request divided by `maxConnections`. When we get errors// we do exponential backoff. As soon as we recover from an error we reset back// to delegate.minDelayMs.function computeDelayAndUpdateDurations( delay: number, delegate: ConnectionLoopDelegate, sendRecords: SendRecord[],): number { const {length} = sendRecords; if (length === 0) { return delay; }
const {ok} = sendRecords[sendRecords.length - 1]; const {maxConnections, minDelayMs} = delegate;
if (!ok) { return delay === 0 ? minDelayMs : delay * 2; }
if (length > 1) { // length > 1 const previous: SendRecord = sendRecords[sendRecords.length - 2];
// Prune while (sendRecords.length > CONNECTION_MEMORY_COUNT) { sendRecords.shift(); }
if (ok && !previous.ok) { // Recovered return minDelayMs; } }
const med = median( sendRecords.filter(({ok}) => ok).map(({duration}) => duration), );
return (med / maxConnections) | 0;}
function median(values: number[]) { values.sort(); const {length} = values; const half = length >> 1; if (length % 2 === 1) { return values[half]; } return (values[half - 1] + values[half]) / 2;}
function didLastSendRequestFail(sendRecords: SendRecord[]) { return sendRecords.length > 0 && !sendRecords[sendRecords.length - 1].ok;}
function recovered(sendRecords: SendRecord[]) { return ( sendRecords.length > 1 && !sendRecords[sendRecords.length - 2].ok && sendRecords[sendRecords.length - 1].ok );}
replicache
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2 years ago
