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

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

Co-authored-by: Daria Pardue <daria.pardue@mongodb.com>

src/utils.ts

@@ -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 ?? {};
@@ -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;
     }
   }
 
@@ -1004,7 +1004,7 @@ export function makeInterruptibleAsyncInterval(
     }
 
     lastCallTime = 0;
-    lastWakeTime = 0;
+    cannotBeExpedited = false;
   }
 
   function reschedule(ms?: number) {
@@ -1017,7 +1017,7 @@ export function makeInterruptibleAsyncInterval(
   }
 
   function executeAndReschedule() {
-    lastWakeTime = 0;
+    cannotBeExpedited = false;
     lastCallTime = clock();
 
     fn(err => {