fix: fast timers and event loop lag (nodejs#1977)

lib/timers.js

@@ -13,13 +13,15 @@ function onTimeout () {
   while (idx < len) {
     const timer = fastTimers[idx]
 
-    if (timer.expires && fastNow >= timer.expires) {
-      timer.expires = 0
+    if (timer.state === 0) {
+      timer.state = fastNow + timer.delay
+    } else if (timer.state > 0 && fastNow >= timer.state) {
+      timer.state = -1
       timer.callback(timer.opaque)
     }
 
-    if (timer.expires === 0) {
-      timer.active = false
+    if (timer.state === -1) {
+      timer.state = -2
       if (idx !== len - 1) {
         fastTimers[idx] = fastTimers.pop()
       } else {
@@ -53,27 +55,29 @@ class Timeout {
     this.callback = callback
     this.delay = delay
     this.opaque = opaque
-    this.expires = 0
-    this.active = false
+
+    //  -2 not in timer list
+    //  -1 in timer list but inactive
+    //   0 in timer list waiting for time
+    // > 0 in timer list waiting for time to expire
+    this.state = -2
 
     this.refresh()
   }
 
   refresh () {
-    if (!this.active) {
-      this.active = true
+    if (this.state === -2) {
       fastTimers.push(this)
       if (!fastNowTimeout || fastTimers.length === 1) {
         refreshTimeout()
-        fastNow = Date.now()
       }
     }
 
-    this.expires = fastNow + this.delay
+    this.state = 0
   }
 
   clear () {
-    this.expires = 0
+    this.state = -1
   }
 }