cli: replace timer map with red-black tree (#3218)

This avoids a crash when the Deno process has been running for
2**32 ms (about 50 days). Additionaly, time complexity of finding which
timer is due to fire next is reduced from from O(n) to O(log n).

cli/js/rbtree.ts

@@ -0,0 +1,241 @@
+// Derived from https://github.com/vadimg/js_bintrees. MIT Licensed.
+
+class RBNode<T> {
+  public left: this | null;
+  public right: this | null;
+  public red: boolean;
+
+  constructor(public data: T) {
+    this.left = null;
+    this.right = null;
+    this.red = true;
+  }
+
+  getChild(dir: boolean | number): this | null {
+    return dir ? this.right : this.left;
+  }
+
+  setChild(dir: boolean | number, val: this | null): void {
+    if (dir) {
+      this.right = val;
+    } else {
+      this.left = val;
+    }
+  }
+}
+
+class RBTree<T> {
+  private root: RBNode<T> | null;
+
+  constructor(private comparator: (a: T, b: T) => number) {
+    this.root = null;
+  }
+
+  // returns null if tree is empty
+  min(): T | null {
+    let res = this.root;
+    if (res === null) {
+      return null;
+    }
+    while (res.left !== null) {
+      res = res.left;
+    }
+    return res.data;
+  }
+
+  // returns node data if found, null otherwise
+  find(data: T): T | null {
+    let res = this.root;
+    while (res !== null) {
+      const c = this.comparator(data, res.data!);
+      if (c === 0) {
+        return res.data;
+      } else {
+        res = res.getChild(c > 0);
+      }
+    }
+    return null;
+  }
+
+  // returns true if inserted, false if duplicate
+  insert(data: T): boolean {
+    let ret = false;
+
+    if (this.root === null) {
+      // empty tree
+      this.root = new RBNode(data);
+      ret = true;
+    } else {
+      const head = new RBNode((null as unknown) as T); // fake tree root
+
+      let dir = 0;
+      let last = 0;
+
+      // setup
+      let gp = null; // grandparent
+      let ggp = head; // grand-grand-parent
+      let p: RBNode<T> | null = null; // parent
+      let node: RBNode<T> | null = this.root;
+      ggp.right = this.root;
+
+      // search down
+      while (true) {
+        if (node === null) {
+          // insert new node at the bottom
+          node = new RBNode(data);
+          p!.setChild(dir, node);
+          ret = true;
+        } else if (isRed(node.left) && isRed(node.right)) {
+          // color flip
+          node.red = true;
+          node.left!.red = false;
+          node.right!.red = false;
+        }
+
+        // fix red violation
+        if (isRed(node) && isRed(p)) {
+          const dir2 = ggp.right === gp;
+
+          if (node === p!.getChild(last)) {
+            ggp.setChild(dir2, singleRotate(gp!, !last));
+          } else {
+            ggp.setChild(dir2, doubleRotate(gp!, !last));
+          }
+        }
+
+        const cmp = this.comparator(node.data!, data);
+
+        // stop if found
+        if (cmp === 0) {
+          break;
+        }
+
+        last = dir;
+        dir = Number(cmp < 0); // Fix type
+
+        // update helpers
+        if (gp !== null) {
+          ggp = gp;
+        }
+        gp = p;
+        p = node;
+        node = node.getChild(dir);
+      }
+
+      // update root
+      this.root = head.right;
+    }
+
+    // make root black
+    this.root!.red = false;
+
+    return ret;
+  }
+
+  // returns true if removed, false if not found
+  remove(data: T): boolean {
+    if (this.root === null) {
+      return false;
+    }
+
+    const head = new RBNode((null as unknown) as T); // fake tree root
+    let node = head;
+    node.right = this.root;
+    let p = null; // parent
+    let gp = null; // grand parent
+    let found = null; // found item
+    let dir: boolean | number = 1;
+
+    while (node.getChild(dir) !== null) {
+      const last = dir;
+
+      // update helpers
+      gp = p;
+      p = node;
+      node = node.getChild(dir)!;
+
+      const cmp = this.comparator(data, node.data);
+
+      dir = cmp > 0;
+
+      // save found node
+      if (cmp === 0) {
+        found = node;
+      }
+
+      // push the red node down
+      if (!isRed(node) && !isRed(node.getChild(dir))) {
+        if (isRed(node.getChild(!dir))) {
+          const sr = singleRotate(node, dir);
+          p.setChild(last, sr);
+          p = sr;
+        } else if (!isRed(node.getChild(!dir))) {
+          const sibling = p.getChild(!last);
+          if (sibling !== null) {
+            if (
+              !isRed(sibling.getChild(!last)) &&
+              !isRed(sibling.getChild(last))
+            ) {
+              // color flip
+              p.red = false;
+              sibling.red = true;
+              node.red = true;
+            } else {
+              const dir2 = gp!.right === p;
+
+              if (isRed(sibling.getChild(last))) {
+                gp!.setChild(dir2, doubleRotate(p, last));
+              } else if (isRed(sibling.getChild(!last))) {
+                gp!.setChild(dir2, singleRotate(p, last));
+              }
+
+              // ensure correct coloring
+              const gpc = gp!.getChild(dir2)!;
+              gpc.red = true;
+              node.red = true;
+              gpc.left!.red = false;
+              gpc.right!.red = false;
+            }
+          }
+        }
+      }
+    }
+
+    // replace and remove if found
+    if (found !== null) {
+      found.data = node.data;
+      p!.setChild(p!.right === node, node.getChild(node.left === null));
+    }
+
+    // update root and make it black
+    this.root = head.right;
+    if (this.root !== null) {
+      this.root.red = false;
+    }
+
+    return found !== null;
+  }
+}
+
+function isRed<T>(node: RBNode<T> | null): boolean {
+  return node !== null && node.red;
+}
+
+function singleRotate<T>(root: RBNode<T>, dir: boolean | number): RBNode<T> {
+  const save = root.getChild(!dir)!;
+
+  root.setChild(!dir, save.getChild(dir));
+  save.setChild(dir, root);
+
+  root.red = true;
+  save.red = false;
+
+  return save;
+}
+
+function doubleRotate<T>(root: RBNode<T>, dir: boolean | number): RBNode<T> {
+  root.setChild(!dir, singleRotate(root.getChild(!dir)!, !dir));
+  return singleRotate(root, dir);
+}
+
+export { RBTree };

cli/js/timers.ts

@@ -3,6 +3,7 @@ import { assert } from "./util.ts";
 import { window } from "./window.ts";
 import * as dispatch from "./dispatch.ts";
 import { sendSync, sendAsync } from "./dispatch_json.ts";
+import { RBTree } from "./rbtree.ts";
 
 const { console } = window;
 
@@ -15,14 +16,6 @@ interface Timer {
   scheduled: boolean;
 }
 
-// We'll subtract EPOCH every time we retrieve the time with Date.now(). This
-// ensures that absolute time values stay below UINT32_MAX - 2, which is the
-// maximum object key that EcmaScript considers "numerical". After running for
-// about a month, this is no longer true, and Deno explodes.
-// TODO(piscisaureus): fix that ^.
-const EPOCH = Date.now();
-const APOCALYPSE = 2 ** 32 - 2;
-
 // Timeout values > TIMEOUT_MAX are set to 1.
 const TIMEOUT_MAX = 2 ** 31 - 1;
 
@@ -30,14 +23,8 @@ let globalTimeoutDue: number | null = null;
 
 let nextTimerId = 1;
 const idMap = new Map<number, Timer>();
-const dueMap: { [due: number]: Timer[] } = Object.create(null);
-
-function getTime(): number {
-  // TODO: use a monotonic clock.
-  const now = Date.now() - EPOCH;
-  assert(now >= 0 && now < APOCALYPSE);
-  return now;
-}
+type DueNode = { due: number; timers: Timer[] };
+const dueTree = new RBTree<DueNode>((a, b) => a.due - b.due);
 
 function clearGlobalTimeout(): void {
   globalTimeoutDue = null;
@@ -73,12 +60,14 @@ function schedule(timer: Timer, now: number): void {
   assert(!timer.scheduled);
   assert(now <= timer.due);
   // Find or create the list of timers that will fire at point-in-time `due`.
-  let list = dueMap[timer.due];
-  if (list === undefined) {
-    list = dueMap[timer.due] = [];
+  const maybeNewDueNode = { due: timer.due, timers: [] };
+  let dueNode = dueTree.find(maybeNewDueNode);
+  if (dueNode === null) {
+    dueTree.insert(maybeNewDueNode);
+    dueNode = maybeNewDueNode;
   }
   // Append the newly scheduled timer to the list and mark it as scheduled.
-  list.push(timer);
+  dueNode!.timers.push(timer);
   timer.scheduled = true;
   // If the new timer is scheduled to fire before any timer that existed before,
   // update the global timeout to reflect this.
@@ -91,21 +80,18 @@ function unschedule(timer: Timer): void {
   if (!timer.scheduled) {
     return;
   }
+  const searchKey = { due: timer.due, timers: [] };
   // Find the list of timers that will fire at point-in-time `due`.
-  const list = dueMap[timer.due];
+  const list = dueTree.find(searchKey)!.timers;
   if (list.length === 1) {
     // Time timer is the only one in the list. Remove the entire list.
     assert(list[0] === timer);
-    delete dueMap[timer.due];
+    dueTree.remove(searchKey);
     // If the unscheduled timer was 'next up', find when the next timer that
     // still exists is due, and update the global alarm accordingly.
     if (timer.due === globalTimeoutDue) {
-      let nextTimerDue: number | null = null;
-      for (const key in dueMap) {
-        nextTimerDue = Number(key);
-        break;
-      }
-      setOrClearGlobalTimeout(nextTimerDue, getTime());
+      const nextDueNode: DueNode | null = dueTree.min();
+      setOrClearGlobalTimeout(nextDueNode && nextDueNode.due, Date.now());
     }
   } else {
     // Multiple timers that are due at the same point in time.
@@ -129,7 +115,7 @@ function fire(timer: Timer): void {
   } else {
     // Interval timer: compute when timer was supposed to fire next.
     // However make sure to never schedule the next interval in the past.
-    const now = getTime();
+    const now = Date.now();
     timer.due = Math.max(now, timer.due + timer.delay);
     schedule(timer, now);
   }
@@ -140,40 +126,27 @@ function fire(timer: Timer): void {
 }
 
 function fireTimers(): void {
-  const now = getTime();
+  const now = Date.now();
   // Bail out if we're not expecting the global timer to fire.
   if (globalTimeoutDue === null || pendingEvents > 0) {
     return;
   }
-  // After firing the timers that are due now, this will hold the due time of
-  // the first timer that hasn't fired yet.
-  let nextTimerDue: number | null = null;
-  // Walk over the keys of the 'due' map. Since dueMap is actually a regular
-  // object and its keys are numerical and smaller than UINT32_MAX - 2,
-  // keys are iterated in ascending order.
-  for (const key in dueMap) {
-    // Convert the object key (a string) to a number.
-    const due = Number(key);
-    // Break out of the loop if the next timer isn't due to fire yet.
-    if (Number(due) > now) {
-      nextTimerDue = due;
-      break;
-    }
-    // Get the list of timers that have this due time, then drop it.
-    const list = dueMap[key];
-    delete dueMap[key];
+  // After firing the timers that are due now, this will hold the first timer
+  // list that hasn't fired yet.
+  let nextDueNode: DueNode | null;
+  while ((nextDueNode = dueTree.min()) !== null && nextDueNode.due <= now) {
+    dueTree.remove(nextDueNode);
     // Fire all the timers in the list.
-    for (const timer of list) {
+    for (const timer of nextDueNode.timers) {
       // With the list dropped, the timer is no longer scheduled.
       timer.scheduled = false;
       // Place the callback on the microtask queue.
       Promise.resolve(timer).then(fire);
     }
   }
-
   // Update the global alarm to go off when the first-up timer that hasn't fired
   // yet is due.
-  setOrClearGlobalTimeout(nextTimerDue, now);
+  setOrClearGlobalTimeout(nextDueNode && nextDueNode.due, now);
 }
 
 export type Args = unknown[];
@@ -201,7 +174,7 @@ function setTimer(
   // In the browser, the delay value must be coercible to an integer between 0
   // and INT32_MAX. Any other value will cause the timer to fire immediately.
   // We emulate this behavior.
-  const now = getTime();
+  const now = Date.now();
   if (delay > TIMEOUT_MAX) {
     console.warn(
       `${delay} does not fit into` +