fix: Defer endpoint release while requests are in flight

karma.conf.js

@@ -59,7 +59,7 @@ module.exports = function (config) {
     customLaunchers: {
       DockerChrome: {
         base: "ChromeHeadless",
-        flags: ["--no-sandbox"],
+        flags: ["--no-sandbox", "--js-flags=--expose-gc"],
       },
     },
   };

src/comlink.ts

@@ -234,6 +234,7 @@ type PendingListenersMap = Map<
 type EndpointWithPendingListeners = {
   endpoint: Endpoint;
   pendingListeners: PendingListenersMap;
+  releaseDeferred?: boolean;
 };
 
 /**
@@ -401,6 +402,10 @@ function closeEndPoint(endpoint: Endpoint) {
 
 export function wrap<T>(ep: Endpoint, target?: any): Remote<T> {
   const pendingListeners : PendingListenersMap = new Map();
+  const epWithPendingListeners: EndpointWithPendingListeners = {
+    endpoint: ep,
+    pendingListeners,
+  };
 
   ep.addEventListener("message", function handleMessage(ev: Event) {
     const { data } = ev as MessageEvent;
@@ -416,10 +421,19 @@ export function wrap<T>(ep: Endpoint, target?: any): Remote<T> {
       resolver(data);
     } finally {
       pendingListeners.delete(data.id);
+      if (
+        epWithPendingListeners.releaseDeferred &&
+        pendingListeners.size === 0
+      ) {
+        epWithPendingListeners.releaseDeferred = false;
+        releaseEndpoint(epWithPendingListeners).finally(() => {
+          pendingListeners.clear();
+        });
+      }
     }
   });
 
-  return createProxy<T>({ endpoint: ep, pendingListeners }, [], target) as any;
+  return createProxy<T>(epWithPendingListeners, [], target) as any;
 }
 
 function throwIfProxyReleased(isReleased: boolean) {
@@ -455,6 +469,10 @@ const proxyFinalizers =
       const newCount = (proxyCounter.get(epWithPendingListeners) || 0) - 1;
       proxyCounter.set(epWithPendingListeners, newCount);
       if (newCount === 0) {
+        if (epWithPendingListeners.pendingListeners.size > 0) {
+          epWithPendingListeners.releaseDeferred = true;
+          return;
+        }
         releaseEndpoint(epWithPendingListeners).finally(() => {
           epWithPendingListeners.pendingListeners.clear();
         });

tests/same_window.comlink.test.js

@@ -598,6 +598,42 @@ describe("Comlink in the same realm", function () {
     expect(finalized).to.be.true;
   });
 
+  it("in-flight requests should not be dropped when proxy is GC'd mid-await", async function () {
+    if (typeof globalThis.gc !== "function") this.skip();
+    this.timeout(15000);
+
+    const hammer = setInterval(() => globalThis.gc(), 50);
+    const garbage = [];
+    const pressure = setInterval(() => {
+      garbage.push(new Uint8Array(2_000_000));
+      if (garbage.length > 20) garbage.length = 0;
+    }, 50);
+
+    try {
+      for (let i = 0; i < 20; i++) {
+        const { port1, port2 } = new MessageChannel();
+        port1.start();
+        port2.start();
+        Comlink.expose(
+          {
+            slow: () => new Promise((r) => setTimeout(() => r("ok"), 100)),
+          },
+          port2
+        );
+        const result = await Promise.race([
+          Comlink.wrap(port1).slow(),
+          new Promise((_, reject) =>
+            setTimeout(() => reject(new Error(`call ${i} hung — port closed mid-await`)), 2000)
+          ),
+        ]);
+        expect(result).to.equal("ok");
+      }
+    } finally {
+      clearInterval(hammer);
+      clearInterval(pressure);
+    }
+  });
+
   // commented out this test as it could be unreliable in various browsers as
   // it has to wait for GC to kick in which could happen at any timing
   // this does seem to work when testing locally