Rewrite the scheduler: more efficient and always finite

lib/collector.js

@@ -7,14 +7,16 @@ const pathlib = require('path');
 const extractors = require('./extractors');
 const Command = require('./commands');
 const {Scope, Module} = require('./scope');
+const CircularList = require('./list');
 
 class Collector {
     constructor(parser, root = '.') {
         this.root = root;
         this.parser = parser;
         this.schemas = [];
-        this.tasks = [];
+        this.tasks = new CircularList;
         this.taskCount = 0;
+        this.active = true;
         this.modules = new Map;
         this.global = Scope.global([]);
         this.running = false;
@@ -82,7 +84,7 @@ class Collector {
                 if (type && type in extractors) {
                     const task = this._collect(node, scope);
 
-                    this.tasks.push(task);
+                    this.tasks.add(task);
                     ++this.taskCount;
 
                     continue;
@@ -109,6 +111,8 @@ class Collector {
         let result = null;
 
         while (true) {
+            this.active = true;
+
             const {done, value} = iter.next(result);
 
             if (done) {
@@ -199,17 +203,28 @@ class Collector {
     }
 
     _schedule() {
-        // TODO: prevent infinite loop.
-
         const {tasks} = this;
 
-        for (let i = 0; tasks.length > 0; i = ++i % tasks.length) {
-            const {done} = tasks[i].next();
+        let marker = null;
+
+        while (!tasks.isEmpty) {
+            const task = tasks.remove();
+
+            const {done} = task.next();
 
             if (done) {
-                // TODO: use linked list instead.
-                tasks.splice(i, 1);
-                --i;
+                marker = null;
+                continue;
+            }
+
+            tasks.add(task);
+
+            if (this.active) {
+                marker = task;
+                this.active = false;
+            } else if (task === marker) {
+                // TODO: warning.
+                return;
             }
         }
     }

lib/list.js

@@ -0,0 +1,51 @@
+'use strict';
+
+const assert = require('assert');
+
+class CircularList {
+    constructor() {
+        this.mark = Symbol();
+        this.prev = null;
+        this.walk = null;
+    }
+
+    get isEmpty() {
+        return !this.walk;
+    }
+
+    add(entry) {
+        assert(!entry[this.mark]);
+
+        if (this.prev) {
+            assert(this.walk);
+
+            this.prev = this.prev[this.mark] = entry;
+        } else {
+            assert(!this.walk);
+
+            this.walk = this.prev = entry;
+        }
+
+        entry[this.mark] = this.walk;
+
+        assert(!this.prev || this.prev[this.mark] === this.walk);
+    }
+
+    remove() {
+        assert(this.walk);
+
+        const removed = this.walk;
+
+        if (removed === this.prev) {
+            this.walk = this.prev = null;
+        } else {
+            this.walk = this.prev[this.mark] = removed[this.mark];
+        }
+
+        removed[this.mark] = null;
+
+        return removed;
+    }
+}
+
+module.exports = CircularList;

tests/externals.json

@@ -24,6 +24,17 @@
             "namespace": "externals.first",
             "fields": [{"name": "d", "type": "double"}]
         },
+        {
+            "type": "record",
+            "name": "X",
+            "namespace": "externals",
+            "fields": [
+                {"name": "a", "type": "externals.first.A"},
+                {"name": "b", "type": "externals.first.B"},
+                {"name": "c", "type": "externals.first.CC"},
+                {"name": "d", "type": "externals.first.D"}
+            ]
+        },
         {
             "type": "record",
             "name": "N",
@@ -48,17 +59,6 @@
             "namespace": "externals.second",
             "fields": [{"name": "p", "type": "double"}]
         },
-        {
-            "type": "record",
-            "name": "X",
-            "namespace": "externals",
-            "fields": [
-                {"name": "a", "type": "externals.first.A"},
-                {"name": "b", "type": "externals.first.B"},
-                {"name": "c", "type": "externals.first.CC"},
-                {"name": "d", "type": "externals.first.D"}
-            ]
-        },
         {
             "type": "record",
             "name": "Y",