# A Slot class for passing a result to a different coroutine

**URL:** <https://trio.discourse.group/t/a-slot-class-for-passing-a-result-to-a-different-coroutine/515>\
**Category:** Show off your work\
**Created:** [May 21, 2024, 12:59am UTC](https://trio.discourse.group/t/a-slot-class-for-passing-a-result-to-a-different-coroutine/515 "2024-05-21T00:59:02Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![merlinz01](https://yyz2.discourse-cdn.com/free1/user_avatar/trio.discourse.group/merlinz01/32/370_2.png) [@merlinz01](https://trio.discourse.group/u/merlinz01)\
**Post date:** [May 21, 2024, 12:59am UTC](https://trio.discourse.group/t/a-slot-class-for-passing-a-result-to-a-different-coroutine/515/1 "2024-05-21T00:59:02Z")

</div>

I just put the class below together for use in a request/response flow. A memory channel seemed overkill for waiting on a single result to be dispatched from a coroutine that reads messages from the connection. I wanted to be able to do this:

```python
    async def connect(self):

        [make the connection]

        hello_slot = Slot()
        self.conn.message_handlers[MessageType.SERVERHELLO] = hello_slot.set
        hello = Message()
        hello.type = MessageType.CLIENTHELLO
        hello.client_hello.clientID = self.config["machine_id"]
        hello.client_hello.auth = self.config["auth_secret"]
        logger.debug("Sending client hello message to server")
        await self.conn.send_message(hello)
        # Might raise a TooSlowError here (timeout)
        server_hello = await self.hello_slot.get(self.config["hello_timeout"])
        del self.conn.message_handlers[MessageType.SERVERHELLO]

        [verify server hello]

```

So I made this little wrapper:

```python
import trio

class Slot:
    def __init__ (self, value=None):
        self.value = value
        self.event = trio.Event()

    async def set(self, value):
        self.value = value
        self.event.set()

    async def get(self, timeout=None):
        if self.event.is_set():
            return self.value
        if timeout is None:
            await self.event.wait()
            return self.value
        async with trio.fail_after(timeout):
            await self.event.wait()
        return self.value

    def get_threadsafe(self, timeout=None):
        return trio.from_thread.run_sync(self.get, timeout)

```

---

<div class="post-metadata">

**Author:** ![merlinz01](https://yyz2.discourse-cdn.com/free1/user_avatar/trio.discourse.group/merlinz01/32/370_2.png) [@merlinz01](https://trio.discourse.group/u/merlinz01)\
**Post date:** [May 21, 2024, 6:54pm UTC](https://trio.discourse.group/t/a-slot-class-for-passing-a-result-to-a-different-coroutine/515/4 "2024-05-21T18:54:28Z")

</div>

Here’s an improved version:

```python
import threading
import trio

class Slot:
    def __init__ (self, value=None, type=None):
        self.value = value
        self.event = trio.Event()
        self.threading_event = threading.Event()

    async def set(self, value):
        self.value = value
        self.event.set()
        self.threading_event.set()

    async def get(self, timeout=None):
        if self.event.is_set():
            return self.value
        if timeout is None:
            await self.event.wait()
            return self.value
        with trio.fail_after(timeout):
            await self.event.wait()
        return self.value

    def get_threadsafe(self, timeout=None):
        if not self.threading_event.wait(timeout):
            raise trio.TooSlowError("Timeout awaiting slot value")
        return self.value

```