Process hangs after Listener closed

[keroxp]

At first, this is very complicated situation.

Problem occurred

• Server process (with Deno.listen()) won't exit even after listener.close() called.
• There are no active resources except rid=0-2

Code

These are very simple request-response type TCP server and client.

server.ts

async function server() {
  const l = Deno.listen({ port: 4444 });
  let buf = new Uint8Array(4);
  const conn = await l.accept();
  const process = async function* () {
    while (true) {
      console.log("[server] reading");
      // Read request with timeout
      const nr = await Promise.race([
        conn.read(buf),
        new Promise((resolve) => {
          setTimeout(resolve, 100);
        })
      ]);
      if (!nr) {
        console.log("[server] read timeout");    
        conn.close();
        return 
      } else {
        console.log("[server] read done", nr);
        console.log("[server] writing");
        const nw = await conn.write(new Uint8Array([0,1,2,3]));
        console.log("[server] written", nw);
      }
    }
  }
  for await (const _ of process());
  l.close();
  console.log("[server] close", Deno.resources());
}
server();

client.ts

const conn = await Deno.connect({ port: 4444 });
async function reqRes() {
  console.log("[cli] writing");
  const nw = await conn.write(new Uint8Array([0,1,2,3]));
  console.log("[cli] written", nw);
  const buf = new Uint8Array(4);
  console.log("[cli] reading");
  const nr = await conn.read(buf);
  console.log("[cli] read done", nr);  
}
// First request-response: 
await reqRes();
// Second request-response: expect error as conn is closed by server
setTimeout(async () => {
  try {
    await reqRes(); 
  } catch (e) {
    console.error(e);    
  } finally {
    conn.close();
  }
  console.log("[cli] close", Deno.resources());
}, 200);

Logs

server.ts

[server] reading
[server] read done 4
[server] writing
[server] written 4
[server] reading
[server] read timeout
[server] close { 0: "stdin", 1: "stdout", 2: "stderr" }
<- hangs

client.ts

[cli] writing
[cli] written 4
[cli] reading
[cli] read done 4
[cli] writing
[cli] written 4
[cli] reading
ConnectionReset: Connection reset by peer (os error 54)
    at Object.constructError ($deno$/errors.ts:43:13)
    at unwrapResponse ($deno$/dispatch_minimal.ts:59:12)
    at Object.sendAsyncMinimal ($deno$/dispatch_minimal.ts:102:10)
    at async Object.read ($deno$/files.ts:154:17)
    at async reqRes (file:///Users/keroxp/src/deno-pg/conn/client.ts:8:14)
    at async file:///Users/keroxp/src/deno-pg/conn/client.ts:16:5
[cli] close { 0: "stdin", 1: "stdout", 2: "stderr" }
<- exit

Guess

Some async handle by conn.read(buf) won't be released after conn.close() or listener.close() called if it hasn't be resolved. I think Closer should cleanup unresolved IO handle.

[bartlomieju]

Most likely the same cause as in #3390

[jsouto18]

This happens because the poll_read is stuck on Poll::Pending. This task needs to be woken on StreamResource drop else it will hang forever.

[ry]

Assigning to @piscisaureus just to keep track of this. We've discussed this in some detail and came to the conclusion that this will require some work to fix.
First thing is we need a smaller test that involves just listen, accept, read.

[bartlomieju]

Fixed in #4293