Keep a hold's release behind MessageHold, and require its listener count

src/held-messages.ts

@@ -25,26 +25,29 @@ type Held = {
 	pduObjs: PduObject[];
 };
 
+type HoldEntry = {
+	isHeld: () => boolean;
+	release: () => void;
+};
+
 /** One message offered to the application, held until it is answered or every listener gives up. */
 export class MessageHold {
-	private readonly held: HeldMessages;
-	private readonly pduObjs: PduObject[];
+	private readonly entry: HoldEntry;
 	private working: number;
 
-	constructor(held: HeldMessages, pduObjs: PduObject[], listeners: number) {
-		this.held = held;
-		this.pduObjs = pduObjs;
+	constructor(entry: HoldEntry, listeners: number) {
+		this.entry = entry;
 		this.working = listeners;
 	}
 
 	/** Whether a drain is still waiting for this message to be answered. */
 	isHeld(): boolean {
-		return this.held.has(this.pduObjs);
+		return this.entry.isHeld();
 	}
 
 	/** A turn later, so a listener sending its receipt straight after the response still holds. */
 	answered(): void {
-		setImmediate(() => { this.held.release(this.pduObjs); });
+		setImmediate(() => { this.entry.release(); });
 	}
 
 	/** A rejection leaves the other listeners running, so only the last one to fail gives the message up. */
@@ -54,9 +57,9 @@ export class MessageHold {
 		if (this.working <= 0) this.answered();
 	}
 
-	/** A message nobody took is not work a shutdown can wait for. */
-	untaken(): void {
-		this.held.release(this.pduObjs);
+	/** At once, for a message nobody took: that is not work a shutdown can wait for. */
+	release(): void {
+		this.entry.release();
 	}
 }
 
@@ -94,9 +97,11 @@ export class HeldMessages {
 		return this.held.full || this.octets >= this.maxOctets;
 	}
 
-	/** Holds a message about to be offered to `listeners` listeners. */
-	hold(pduObjs: PduObject[], listeners = 1): MessageHold {
-		const hold = new MessageHold(this, pduObjs, listeners);
+	hold(pduObjs: PduObject[], listeners: number): MessageHold {
+		const hold = new MessageHold({
+			isHeld: () => this.has(pduObjs),
+			release: () => { this.release(pduObjs); },
+		}, listeners);
 		const key = keyOf(pduObjs);
 
 		if (key === undefined) return hold;
@@ -118,14 +123,13 @@ export class HeldMessages {
 		return hold;
 	}
 
-	/** Whether a drain is still waiting for this message to be answered. */
-	has(pduObjs: PduObject[]): boolean {
+	private has(pduObjs: PduObject[]): boolean {
 		const key = keyOf(pduObjs);
 
 		return key !== undefined && this.held.get(key)?.pduObjs === pduObjs;
 	}
 
-	release(pduObjs: PduObject[]): void {
+	private release(pduObjs: PduObject[]): void {
 		const key = keyOf(pduObjs);
 
 		// Identity, not the key: a wrapped sequence number must not release someone else's message.