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fix(NODE-3116): reschedule unreliable async interval first #3006

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merged 3 commits into from
Nov 5, 2021
Merged

fix(NODE-3116): reschedule unreliable async interval first #3006

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a82228b
fix(NODE-3116): reschedule unreliable async interval first
durran Oct 18, 2021
b9d3dca
test: refactor unit tests to be more clear
durran Nov 4, 2021
e425b7e
refactor: simplify async timer logic (#3028)
dariakp Nov 5, 2021
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32 changes: 16 additions & 16 deletions src/utils.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -954,7 +954,7 @@ export function makeInterruptibleAsyncInterval(
): InterruptibleAsyncInterval {
let timerId: NodeJS.Timeout | undefined;
let lastCallTime: number;
let lastWakeTime: number;
let cannotBeExpedited = false;
let stopped = false;

options = options ?? {};
Expand All @@ -965,34 +965,34 @@ export function makeInterruptibleAsyncInterval(

function wake() {
const currentTime = clock();
const timeSinceLastWake = currentTime - lastWakeTime;
const timeSinceLastCall = currentTime - lastCallTime;
const timeUntilNextCall = interval - timeSinceLastCall;
lastWakeTime = currentTime;
const nextScheduledCallTime = lastCallTime + interval;
const timeUntilNextCall = nextScheduledCallTime - currentTime;

// For the streaming protocol: there is nothing obviously stopping this
// interval from being woken up again while we are waiting "infinitely"
// for `fn` to be called again`. Since the function effectively
// never completes, the `timeUntilNextCall` will continue to grow
// negatively unbounded, so it will never trigger a reschedule here.

// This is possible in virtualized environments like AWS Lambda where our
// clock is unreliable. In these cases the timer is "running" but never
// actually completes, so we want to execute immediately and then attempt
// to reschedule.
if (timeUntilNextCall < 0) {
executeAndReschedule();
return;
}

// debounce multiple calls to wake within the `minInterval`
if (timeSinceLastWake < minInterval) {
if (cannotBeExpedited) {
return;
}

// reschedule a call as soon as possible, ensuring the call never happens
// faster than the `minInterval`
if (timeUntilNextCall > minInterval) {
reschedule(minInterval);
}

// This is possible in virtualized environments like AWS Lambda where our
// clock is unreliable. In these cases the timer is "running" but never
// actually completes, so we want to execute immediately and then attempt
// to reschedule.
if (timeUntilNextCall < 0) {
executeAndReschedule();
cannotBeExpedited = true;
}
}

Expand All @@ -1004,7 +1004,7 @@ export function makeInterruptibleAsyncInterval(
}

lastCallTime = 0;
lastWakeTime = 0;
cannotBeExpedited = false;
}

function reschedule(ms?: number) {
Expand All @@ -1017,7 +1017,7 @@ export function makeInterruptibleAsyncInterval(
}

function executeAndReschedule() {
lastWakeTime = 0;
cannotBeExpedited = false;
lastCallTime = clock();

fn(err => {
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