perf: improve async op santizer speed and accuracy (#20501)

This commit improves async op sanitizer speed by only delaying metrics
collection if there are pending ops. This
results in a speedup of around 30% for small CPU bound unit tests.

It performs this check and possible delay on every collection now,
fixing an issue with parent test leaks into steps.

cli/js/40_testing.js

@@ -40,25 +40,39 @@ let hasSetOpSanitizerDelayMacrotask = false;
 // that resolves when it's (probably) fine to run the op sanitizer.
 //
 // This is implemented by adding a macrotask callback that runs after the
-// timer macrotasks, so we can guarantee that a currently running interval
-// will have an associated op. An additional `setTimeout` of 0 is needed
-// before that, though, in order to give time for worker message ops to finish
-// (since timeouts of 0 don't queue tasks in the timer queue immediately).
-function opSanitizerDelay() {
+// all ready async ops resolve, and the timer macrotask. Using just a macrotask
+// callback without delaying is sufficient, because when the macrotask callback
+// runs after async op dispatch, we know that all async ops that can currently
+// return `Poll::Ready` have done so, and have been dispatched to JS.
+//
+// Worker ops are an exception to this, because there is no way for the user to
+// await shutdown of the worker from the thread calling `worker.terminate()`.
+// Because of this, we give extra leeway for worker ops to complete, by waiting
+// for a whole millisecond if there are pending worker ops.
+function opSanitizerDelay(hasPendingWorkerOps) {
   if (!hasSetOpSanitizerDelayMacrotask) {
     core.setMacrotaskCallback(handleOpSanitizerDelayMacrotask);
     hasSetOpSanitizerDelayMacrotask = true;
   }
-  return new Promise((resolve) => {
+  const p = new Promise((resolve) => {
+    // Schedule an async op to complete immediately to ensure the macrotask is
+    // run. We rely on the fact that enqueueing the resolver callback during the
+    // timeout callback will mean that the resolver gets called in the same
+    // event loop tick as the timeout callback.
     setTimeout(() => {
       ArrayPrototypePush(opSanitizerDelayResolveQueue, resolve);
-    }, 1);
+    }, hasPendingWorkerOps ? 1 : 0);
   });
+  return p;
 }
 
 function handleOpSanitizerDelayMacrotask() {
-  ArrayPrototypeShift(opSanitizerDelayResolveQueue)?.();
-  return opSanitizerDelayResolveQueue.length === 0;
+  const resolve = ArrayPrototypeShift(opSanitizerDelayResolveQueue);
+  if (resolve) {
+    resolve();
+    return opSanitizerDelayResolveQueue.length === 0;
+  }
+  return undefined; // we performed no work, so can skip microtasks checkpoint
 }
 
 // An async operation to $0 was started in this test, but never completed. This is often caused by not $1.
@@ -126,7 +140,8 @@ const OP_DETAILS = {
   "op_tls_start": ["start a TLS connection", "awaiting a `Deno.startTls` call"],
   "op_truncate_async": ["truncate a file", "awaiting the result of a `Deno.truncate` call"],
   "op_utime_async": ["change file timestamps", "awaiting the result of a `Deno.utime` call"],
-  "op_worker_recv_message": ["receive a message from a web worker", "terminating a `Worker`"],
+  "op_host_recv_message": ["receive a message from a web worker", "terminating a `Worker`"],
+  "op_host_recv_ctrl": ["receive a message from a web worker", "terminating a `Worker`"],
   "op_ws_close": ["close a WebSocket", "awaiting until the `close` event is emitted on a `WebSocket`, or the `WebSocketStream#closed` promise resolves"],
   "op_ws_create": ["create a WebSocket", "awaiting until the `open` event is emitted on a `WebSocket`, or the result of a `WebSocketStream#connection` promise"],
   "op_ws_next_event": ["receive the next message on a WebSocket", "closing a `WebSocket` or `WebSocketStream`"],
@@ -136,6 +151,28 @@ const OP_DETAILS = {
   "op_ws_send_pong": ["send a message on a WebSocket", "closing a `WebSocket` or `WebSocketStream`"],
 };
 
+function collectReliableOpMetrics() {
+  let metrics = core.metrics();
+  if (metrics.opsDispatched > metrics.opsCompleted) {
+    // If there are still async ops pending, we drain the event loop to the
+    // point where all ops that can return `Poll::Ready` have done so, to ensure
+    // that any ops are ready because of user cleanup code are completed.
+    const hasPendingWorkerOps = metrics.ops.op_host_recv_message && (
+      metrics.ops.op_host_recv_message.opsDispatched >
+        metrics.ops.op_host_recv_message.opsCompleted ||
+      metrics.ops.op_host_recv_ctrl.opsDispatched >
+        metrics.ops.op_host_recv_ctrl.opsCompleted
+    );
+    return opSanitizerDelay(hasPendingWorkerOps).then(() => {
+      metrics = core.metrics();
+      const traces = new Map(core.opCallTraces);
+      return { metrics, traces };
+    });
+  }
+  const traces = new Map(core.opCallTraces);
+  return { metrics, traces };
+}
+
 // Wrap test function in additional assertion that makes sure
 // the test case does not leak async "ops" - ie. number of async
 // completed ops after the test is the same as number of dispatched
@@ -144,19 +181,26 @@ const OP_DETAILS = {
 function assertOps(fn) {
   /** @param desc {TestDescription | TestStepDescription} */
   return async function asyncOpSanitizer(desc) {
-    const pre = core.metrics();
-    const preTraces = new Map(core.opCallTraces);
+    let metrics = collectReliableOpMetrics();
+    if (metrics.then) {
+      // We're delaying so await to get the result asynchronously.
+      metrics = await metrics;
+    }
+    const { metrics: pre, traces: preTraces } = metrics;
+    let post;
+    let postTraces;
+
     try {
       const innerResult = await fn(desc);
       if (innerResult) return innerResult;
     } finally {
-      // Defer until next event loop turn - that way timeouts and intervals
-      // cleared can actually be removed from resource table, otherwise
-      // false positives may occur (https://github.com/denoland/deno/issues/4591)
-      await opSanitizerDelay();
+      let metrics = collectReliableOpMetrics();
+      if (metrics.then) {
+        // We're delaying so await to get the result asynchronously.
+        metrics = await metrics;
+      }
+      ({ metrics: post, traces: postTraces } = metrics);
     }
-    const post = core.metrics();
-    const postTraces = new Map(core.opCallTraces);
 
     // We're checking diff because one might spawn HTTP server in the background
     // that will be a pending async op before test starts.
@@ -232,6 +276,7 @@ function assertOps(fn) {
         ArrayPrototypePush(details, message);
       }
     }
+
     return { failed: { leakedOps: [details, core.isOpCallTracingEnabled()] } };
   };
 }

cli/tests/testdata/test/ops_sanitizer_step_leak.out

@@ -0,0 +1,10 @@
+Check [WILDCARD]/cli/tests/testdata/test/ops_sanitizer_step_leak.ts
+running 1 test from ./cli/tests/testdata/test/ops_sanitizer_step_leak.ts
+timeout ...
+  step ... ok [WILDCARD]
+------- output -------
+done
+----- output end -----
+timeout ... ok [WILDCARD]
+
+ok | 1 passed (1 step) | 0 failed [WILDCARD]

cli/tests/testdata/test/ops_sanitizer_step_leak.ts

@@ -0,0 +1,10 @@
+Deno.test("timeout", async (t) => {
+  const timer = setTimeout(() => {
+    console.log("timeout");
+  }, 10000);
+  clearTimeout(timer);
+  await t.step("step", async () => {
+    await new Promise<void>((resolve) => setTimeout(() => resolve(), 10));
+  });
+  console.log("done");
+});

cli/tests/unit/fetch_test.ts

@@ -1752,7 +1752,8 @@ Deno.test(
     // if transfer-encoding is sent, content-length is ignored
     // even if it has an invalid value (content-length > totalLength)
     const listener = invalidServer(addr, body);
-    const response = await fetch(`http://${addr}/`);
+    const client = Deno.createHttpClient({});
+    const response = await fetch(`http://${addr}/`, { client });
 
     const res = await response.arrayBuffer();
     const buf = new TextEncoder().encode(data);
@@ -1760,6 +1761,7 @@ Deno.test(
     assertEquals(new Uint8Array(res), buf);
 
     listener.close();
+    client.close();
   },
 );
 
@@ -1781,21 +1783,23 @@ Deno.test(
 
     // It should fail if multiple content-length headers with different values are sent
     const listener = invalidServer(addr, body);
+    const client = Deno.createHttpClient({});
     await assertRejects(
       async () => {
-        await fetch(`http://${addr}/`);
+        await fetch(`http://${addr}/`, { client });
       },
       TypeError,
       "invalid content-length parsed",
     );
 
     listener.close();
+    client.close();
   },
 );
 
 Deno.test(
   { permissions: { net: true } },
-  async function fetchWithInvalidContentLength(): Promise<
+  async function fetchWithInvalidContentLength2(): Promise<
     void
   > {
     const addr = `127.0.0.1:${listenPort}`;
@@ -1807,7 +1811,8 @@ Deno.test(
     );
 
     const listener = invalidServer(addr, body);
-    const response = await fetch(`http://${addr}/`);
+    const client = Deno.createHttpClient({});
+    const response = await fetch(`http://${addr}/`, { client });
 
     // If content-length < totalLength, a maximum of content-length bytes
     // should be returned.
@@ -1817,12 +1822,13 @@ Deno.test(
     assertEquals(new Uint8Array(res), buf.subarray(contentLength));
 
     listener.close();
+    client.close();
   },
 );
 
 Deno.test(
   { permissions: { net: true } },
-  async function fetchWithInvalidContentLength(): Promise<
+  async function fetchWithInvalidContentLength3(): Promise<
     void
   > {
     const addr = `127.0.0.1:${listenPort}`;
@@ -1834,7 +1840,8 @@ Deno.test(
     );
 
     const listener = invalidServer(addr, body);
-    const response = await fetch(`http://${addr}/`);
+    const client = Deno.createHttpClient({});
+    const response = await fetch(`http://${addr}/`, { client });
     // If content-length > totalLength, a maximum of content-length bytes
     // should be returned.
     await assertRejects(
@@ -1846,6 +1853,7 @@ Deno.test(
     );
 
     listener.close();
+    client.close();
   },
 );
 
@@ -1935,10 +1943,12 @@ Deno.test(
       },
     });
 
+    const client = Deno.createHttpClient({});
     const err = await assertRejects(() =>
       fetch(`http://localhost:${listenPort}/`, {
         body: stream,
         method: "POST",
+        client,
       })
     );
 
@@ -1948,6 +1958,7 @@ Deno.test(
     assertEquals(err.cause.message, "foo");
 
     await server;
+    client.close();
   },
 );
 

cli/tests/unit/http_test.ts

@@ -198,12 +198,14 @@ Deno.test(
       await respondWith(new Response(stream.readable));
     })();
 
-    const resp = await fetch(`http://127.0.0.1:${listenPort}/`);
+    const client = Deno.createHttpClient({});
+    const resp = await fetch(`http://127.0.0.1:${listenPort}/`, { client });
     const respBody = await resp.text();
     assertEquals("hello world", respBody);
     await promise;
     httpConn!.close();
     listener.close();
+    client.close();
   },
 );
 
@@ -216,8 +218,8 @@ Deno.test(
     writer.write(new TextEncoder().encode("world"));
     writer.close();
 
+    const listener = Deno.listen({ port: listenPort });
     const promise = (async () => {
-      const listener = Deno.listen({ port: listenPort });
       const conn = await listener.accept();
       const httpConn = Deno.serveHttp(conn);
       const evt = await httpConn.nextRequest();
@@ -235,14 +237,17 @@ Deno.test(
       listener.close();
     })();
 
+    const client = Deno.createHttpClient({});
     const resp = await fetch(`http://127.0.0.1:${listenPort}/`, {
       body: stream.readable,
       method: "POST",
       headers: { "connection": "close" },
+      client,
     });
 
     await resp.arrayBuffer();
     await promise;
+    client.close();
   },
 );
 
@@ -375,9 +380,11 @@ Deno.test(
       await respondWith(new Response("response"));
     })();
 
+    const client = Deno.createHttpClient({});
     const resp = await fetch(`http://127.0.0.1:${listenPort}/`, {
       method: "POST",
       body: "request",
+      client,
     });
     const respBody = await resp.text();
     assertEquals("response", respBody);
@@ -385,6 +392,7 @@ Deno.test(
 
     httpConn!.close();
     listener.close();
+    client.close();
   },
 );
 
@@ -427,9 +435,11 @@ Deno.test(
       listener.close();
     })();
 
+    const client = Deno.createHttpClient({});
     const resp = await fetch(`http://127.0.0.1:${listenPort}/`);
     await resp.body!.cancel();
     await promise;
+    client.close();
   },
 );
 
@@ -788,7 +798,11 @@ Deno.test({ permissions: { net: true } }, async function httpServerWebSocket() {
       socket.send(m.data);
       socket.close(1001);
     };
+    const close = new Promise<void>((resolve) => {
+      socket.onclose = () => resolve();
+    });
     await respondWith(response);
+    await close;
   })();
 
   const def = deferred();
@@ -1228,11 +1242,15 @@ Deno.test(
     async function client() {
       const socket = new WebSocket(`ws://${hostname}:${port}/`);
       socket.onopen = () => socket.send("bla bla");
+      const closed = new Promise<void>((resolve) => {
+        socket.onclose = () => resolve();
+      });
       const { data } = await new Promise<MessageEvent<string>>((res) =>
         socket.onmessage = res
       );
       assertStrictEquals(data, "bla bla");
       socket.close();
+      await closed;
     }
 
     await Promise.all([server(), client()]);

cli/tests/unit/net_test.ts

@@ -901,7 +901,7 @@ Deno.test(
 );
 
 Deno.test({ permissions: { net: true } }, async function whatwgStreams() {
-  (async () => {
+  const server = (async () => {
     const listener = Deno.listen({ hostname: "127.0.0.1", port: listenPort });
     const conn = await listener.accept();
     await conn.readable.pipeTo(conn.writable);
@@ -920,6 +920,7 @@ Deno.test({ permissions: { net: true } }, async function whatwgStreams() {
   assert(!done);
   assertEquals(decoder.decode(value), "Hello World");
   await reader.cancel();
+  await server;
 });
 
 Deno.test(
@@ -973,7 +974,7 @@ Deno.test(
 
 Deno.test(
   { permissions: { read: true, run: true } },
-  async function netListenUnref() {
+  async function netListenUnref2() {
     const [statusCode, _output] = await execCode(`
       async function main() {
         const listener = Deno.listen({ port: ${listenPort} });

cli/tests/unit/serve_test.ts

@@ -965,7 +965,8 @@ function createStreamTest(count: number, delay: number, action: string) {
 
     try {
       await listeningPromise;
-      const resp = await fetch(`http://127.0.0.1:${servePort}/`);
+      const client = Deno.createHttpClient({});
+      const resp = await fetch(`http://127.0.0.1:${servePort}/`, { client });
       if (action == "Throw") {
         await assertRejects(async () => {
           await resp.text();
@@ -980,6 +981,7 @@ function createStreamTest(count: number, delay: number, action: string) {
 
         assertEquals(text, expected);
       }
+      client.close();
     } finally {
       ac.abort();
       await server.shutdown();
@@ -1096,12 +1098,14 @@ Deno.test(
     });
 
     await listeningPromise;
-    const resp = await fetch(`http://127.0.0.1:${servePort}/`);
+    const client = Deno.createHttpClient({});
+    const resp = await fetch(`http://127.0.0.1:${servePort}/`, { client });
     const respBody = await resp.text();
 
     assertEquals("", respBody);
     ac.abort();
     await server.finished;
+    client.close();
   },
 );
 
@@ -1138,12 +1142,14 @@ Deno.test(
     });
 
     await listeningPromise;
-    const resp = await fetch(`http://127.0.0.1:${servePort}/`);
+    const client = Deno.createHttpClient({});
+    const resp = await fetch(`http://127.0.0.1:${servePort}/`, { client });
     // Incorrectly implemented reader ReadableStream should reject.
     assertStringIncludes(await resp.text(), "Failed to execute 'enqueue'");
     await errorPromise;
     ac.abort();
     await server.finished;
+    client.close();
   },
 );
 
@@ -1187,6 +1193,7 @@ Deno.test(
 Deno.test({ permissions: { net: true } }, async function httpServerWebSocket() {
   const ac = new AbortController();
   const listeningPromise = deferred();
+  const done = deferred();
   const server = Deno.serve({
     handler: (request) => {
       const {
@@ -1201,6 +1208,7 @@ Deno.test({ permissions: { net: true } }, async function httpServerWebSocket() {
         socket.send(m.data);
         socket.close(1001);
       };
+      socket.onclose = () => done.resolve();
       return response;
     },
     port: servePort,
@@ -1221,6 +1229,7 @@ Deno.test({ permissions: { net: true } }, async function httpServerWebSocket() {
   ws.onopen = () => ws.send("foo");
 
   await def;
+  await done;
   ac.abort();
   await server.finished;
 });
@@ -1308,6 +1317,7 @@ Deno.test(
   { permissions: { net: true } },
   async function httpServerWebSocketUpgradeTwice() {
     const ac = new AbortController();
+    const done = deferred();
     const listeningPromise = deferred();
     const server = Deno.serve({
       handler: (request) => {
@@ -1330,6 +1340,7 @@ Deno.test(
           socket.send(m.data);
           socket.close(1001);
         };
+        socket.onclose = () => done.resolve();
         return response;
       },
       port: servePort,
@@ -1350,6 +1361,7 @@ Deno.test(
     ws.onopen = () => ws.send("foo");
 
     await def;
+    await done;
     ac.abort();
     await server.finished;
   },
@@ -1359,6 +1371,7 @@ Deno.test(
   { permissions: { net: true } },
   async function httpServerWebSocketCloseFast() {
     const ac = new AbortController();
+    const done = deferred();
     const listeningPromise = deferred();
     const server = Deno.serve({
       handler: (request) => {
@@ -1367,6 +1380,7 @@ Deno.test(
           socket,
         } = Deno.upgradeWebSocket(request);
         socket.onopen = () => socket.close();
+        socket.onclose = () => done.resolve();
         return response;
       },
       port: servePort,
@@ -1385,6 +1399,7 @@ Deno.test(
     ws.onclose = () => def.resolve();
 
     await def;
+    await done;
     ac.abort();
     await server.finished;
   },
@@ -1394,6 +1409,7 @@ Deno.test(
   { permissions: { net: true } },
   async function httpServerWebSocketCanAccessRequest() {
     const ac = new AbortController();
+    const done = deferred();
     const listeningPromise = deferred();
     const server = Deno.serve({
       handler: (request) => {
@@ -1409,6 +1425,7 @@ Deno.test(
           socket.send(request.url.toString());
           socket.close(1001);
         };
+        socket.onclose = () => done.resolve();
         return response;
       },
       port: servePort,
@@ -1430,6 +1447,7 @@ Deno.test(
     ws.onopen = () => ws.send("foo");
 
     await def;
+    await done;
     ac.abort();
     await server.finished;
   },
@@ -1588,9 +1606,11 @@ Deno.test(
     );
 
     const { readable, writable } = new TransformStream();
+    const client = Deno.createHttpClient({});
     const resp = await fetch(`http://127.0.0.1:${servePort}/`, {
       method: "POST",
       body: readable,
+      client,
     });
 
     await promise;
@@ -1598,6 +1618,7 @@ Deno.test(
     await testDuplex(resp.body.getReader(), writable.getWriter());
     ac.abort();
     await server.finished;
+    client.close();
   },
 );
 
@@ -1632,9 +1653,11 @@ Deno.test(
     );
 
     const { readable, writable } = new TransformStream();
+    const client = Deno.createHttpClient({});
     const resp = await fetch(`http://127.0.0.1:${servePort}/`, {
       method: "POST",
       body: readable,
+      client,
     });
 
     await promise;
@@ -1642,6 +1665,7 @@ Deno.test(
     await testDuplex(resp.body.getReader(), writable.getWriter());
     ac.abort();
     await server.finished;
+    client.close();
   },
 );
 
@@ -2600,9 +2624,12 @@ for (const testCase of compressionTestCases) {
         });
         try {
           await listeningPromise;
+          const client = Deno.createHttpClient({});
           const resp = await fetch(`http://127.0.0.1:${servePort}/`, {
             headers: testCase.in as HeadersInit,
+            client,
           });
+          client.close();
           await promise;
           const body = await resp.arrayBuffer();
           if (testCase.expect == null) {
@@ -3192,14 +3219,16 @@ Deno.test(
     let count = 0;
     const server = Deno.serve({
       async onListen({ port }: { port: number }) {
-        const res1 = await fetch(`http://localhost:${port}/`);
+        const client = Deno.createHttpClient({});
+        const res1 = await fetch(`http://localhost:${port}/`, { client });
         assertEquals(await res1.text(), "hello world 1");
 
-        const res2 = await fetch(`http://localhost:${port}/`);
+        const res2 = await fetch(`http://localhost:${port}/`, { client });
         assertEquals(await res2.text(), "hello world 2");
 
         promise.resolve();
         ac.abort();
+        client.close();
       },
       signal: ac.signal,
     }, () => {
@@ -3252,13 +3281,16 @@ Deno.test(
 
     try {
       const port = await listeningPromise;
+      const client = Deno.createHttpClient({});
       const resp = await fetch(`http://localhost:${port}/`, {
         headers: { connection: "close" },
         method: "POST",
         body: '{"sus":true}',
+        client,
       });
       const text = await resp.text();
       assertEquals(text, "ok");
+      client.close();
     } finally {
       ac.abort();
       await server.finished;

cli/tests/unit/streams_test.ts

@@ -1,6 +1,5 @@
 // Copyright 2018-2023 the Deno authors. All rights reserved. MIT license.
-import { fail } from "https://deno.land/std@v0.42.0/testing/asserts.ts";
-import { assertEquals, Deferred, deferred } from "./test_util.ts";
+import { assertEquals, Deferred, deferred, fail } from "./test_util.ts";
 
 const {
   core,

cli/tests/unit_node/child_process_test.ts

@@ -497,9 +497,15 @@ Deno.test({
     );
     const childProcess = spawn(Deno.execPath(), ["run", script]);
     const p = withTimeout();
+    const pStdout = withTimeout();
+    const pStderr = withTimeout();
     childProcess.on("exit", () => p.resolve());
+    childProcess.stdout.on("close", () => pStdout.resolve());
+    childProcess.stderr.on("close", () => pStderr.resolve());
     childProcess.kill("SIGKILL");
     await p;
+    await pStdout;
+    await pStderr;
     assert(childProcess.killed);
     assertEquals(childProcess.signalCode, "SIGKILL");
     assertExists(childProcess.exitCode);
@@ -633,9 +639,15 @@ Deno.test({
     // Spawn an infinite cat
     const cp = spawn("cat", ["-"]);
     const p = withTimeout();
+    const pStdout = withTimeout();
+    const pStderr = withTimeout();
     cp.on("exit", () => p.resolve());
+    cp.stdout.on("close", () => pStdout.resolve());
+    cp.stderr.on("close", () => pStderr.resolve());
     cp.kill("SIGIOT");
     await p;
+    await pStdout;
+    await pStderr;
     assert(cp.killed);
     assertEquals(cp.signalCode, "SIGIOT");
   },

cli/tests/unit_node/net_test.ts

@@ -143,12 +143,17 @@ Deno.test("[node/net] multiple Sockets should get correct server data", async ()
   }
 
   const finished = deferred();
+  const serverSocketsClosed: Deferred<undefined>[] = [];
   const server = net.createServer();
   server.on("connection", (socket) => {
     assert(socket !== undefined);
+    const i = serverSocketsClosed.push(deferred());
     socket.on("data", (data) => {
       socket.write(new TextDecoder().decode(data));
     });
+    socket.on("close", () => {
+      serverSocketsClosed[i - 1].resolve();
+    });
   });
 
   const sockets: TestSocket[] = [];
@@ -190,6 +195,7 @@ Deno.test("[node/net] multiple Sockets should get correct server data", async ()
   });
 
   await finished;
+  await Promise.all(serverSocketsClosed);
 
   for (let i = 0; i < socketCount; i++) {
     assertEquals(sockets[i].events, [`${i}`.repeat(3), `${i}`.repeat(3)]);

ext/broadcast_channel/01_broadcast_channel.js

@@ -15,8 +15,9 @@ import DOMException from "ext:deno_web/01_dom_exception.js";
 const primordials = globalThis.__bootstrap.primordials;
 const {
   ArrayPrototypeIndexOf,
-  ArrayPrototypeSplice,
   ArrayPrototypePush,
+  ArrayPrototypeSplice,
+  PromisePrototypeThen,
   Symbol,
   Uint8Array,
 } = primordials;
@@ -70,7 +71,7 @@ function dispatch(source, name, data) {
 // for that reason: it lets promises make forward progress but can
 // still starve other parts of the event loop.
 function defer(go) {
-  setTimeout(go, 1);
+  PromisePrototypeThen(core.ops.op_void_async_deferred(), () => go());
 }
 
 class BroadcastChannel extends EventTarget {

ext/fetch/26_fetch.js

@@ -284,6 +284,9 @@ async function mainFetch(req, recursive, terminator) {
         cause: requestSendError,
       });
     }
+    if (requestBodyRid !== null) {
+      core.tryClose(requestBodyRid);
+    }
     throw err;
   } finally {
     if (cancelHandleRid !== null) {