Fix clearTimer bug (#3143)

cli/js/timers.ts

@@ -44,16 +44,19 @@ function clearGlobalTimeout(): void {
   sendSync(dispatch.OP_GLOBAL_TIMER_STOP);
 }
 
+let pendingEvents = 0;
+
 async function setGlobalTimeout(due: number, now: number): Promise<void> {
   // Since JS and Rust don't use the same clock, pass the time to rust as a
   // relative time value. On the Rust side we'll turn that into an absolute
   // value again.
   const timeout = due - now;
   assert(timeout >= 0);
-
   // Send message to the backend.
   globalTimeoutDue = due;
+  pendingEvents++;
   await sendAsync(dispatch.OP_GLOBAL_TIMER, { timeout });
+  pendingEvents--;
   // eslint-disable-next-line @typescript-eslint/no-use-before-define
   fireTimers();
 }
@@ -139,7 +142,7 @@ function fire(timer: Timer): void {
 function fireTimers(): void {
   const now = getTime();
   // Bail out if we're not expecting the global timer to fire.
-  if (globalTimeoutDue === null) {
+  if (globalTimeoutDue === null || pendingEvents > 0) {
     return;
   }
   // After firing the timers that are due now, this will hold the due time of

cli/js/timers_test.ts

@@ -289,3 +289,15 @@ test(function testFunctionParamsLength(): void {
 test(function clearTimeoutAndClearIntervalNotBeEquals(): void {
   assertNotEquals(clearTimeout, clearInterval);
 });
+
+test(async function timerMaxCpuBug(): Promise<void> {
+  // There was a bug where clearing a timeout would cause Deno to use 100% CPU.
+  clearTimeout(setTimeout(() => {}, 1000));
+  // We can check this by counting how many ops have triggered in the interim.
+  // Certainly less than 10 ops should have been dispatched in next 100 ms.
+  const { opsDispatched } = Deno.metrics();
+  await waitForMs(100);
+  const opsDispatched_ = Deno.metrics().opsDispatched;
+  console.log("opsDispatched", opsDispatched, "opsDispatched_", opsDispatched_);
+  assert(opsDispatched_ - opsDispatched < 10);
+});