add support for global graph listeners

src/graph.test.ts

@@ -1209,6 +1209,31 @@ describe('Components', () => {
     })
 })
 
+describe('Listeners', () => {
+    test('smoke', () => {
+        let listenCallbackCounter = 0
+        const creator = new Graferse()
+        creator.addListener(() => { listenCallbackCounter++ })
+
+        // no one has been called yet
+        expect(listenCallbackCounter).toEqual(0)
+
+        // clearAllLocks invokes listeners
+        creator.clearAllLocks("test")
+        expect(listenCallbackCounter).toEqual(1)
+
+        // notifyWaiters invokes listeners
+        creator.notifyWaiters(new Set())
+        expect(listenCallbackCounter).toEqual(2)
+
+        // recursive calling of notifyWaiters
+        creator.lastCallCache.set("agent1", () => creator.notifyWaiters(new Set()))
+        creator.notifyWaiters(new Set(["agent1"]))
+        // listener is invoked once for each agent
+        expect(listenCallbackCounter).toEqual(4)
+    })
+})
+
 describe('Exceptions', () => {
     test('node not on path', () => {
         const getLockForLink = (from: Lock, to: Lock) => {

src/graph.ts

@@ -131,6 +131,7 @@ class Graferse
     linkLocks: LinkLock[] = []
     lockGroups: Lock[][] = []
     lastCallCache = new Map<string,() => void>()
+    listeners: Array<() => void> = []
 
     makeLock() {
         const lock = new Lock()
@@ -144,6 +145,16 @@ class Graferse
         return linkLock
     }
 
+    addListener(listener: () => void) {
+        this.listeners.push(listener)
+    }
+
+    notifyListeners() {
+        for (const listener of this.listeners) {
+            listener()
+        }
+    }
+
     notifyWaiters(whoCanMoveNow: Set<string>) {
         for (const waiter of whoCanMoveNow) {
             const lastCall = this.lastCallCache.get(waiter)
@@ -152,6 +163,7 @@ class Graferse
             }
             lastCall()
         }
+        this.notifyListeners()
     }
 
     clearAllLocks(byWhom: string) {