Memory not released for WASI resources

[teebee64]

I'm experiencing continuous memory growth when running a long-lived Python WebAssembly component compiled using componentize-py and executed via wasmtime.

Any time a wasi resource is created (e.g. a Fields resource from wasi-http or any other wasi resource), the resource appears to stay in memory after it goes out of scope. This is in contrast to typical Python objects (like lists or dictionaries) which are correctly garbage-collected.

In my application i have implemented a Server-Sent Events (SSE) client that continuously reads data from an InputStream resource from wasi-io. Each time the read function is executed, the data that has been read also stays in memory. So over time, as the SSE client keeps receiving data, the memory keeps increasing until a MemoryError is received.

Here's the relevant code snippet:

incomingBody: wasi_http_types.IncomingBody = self._response.consume()
with incomingBody:
    inputStream: streams.InputStream = incomingBody.stream()
    with inputStream:
        while True:
            try:
                pollable: poll.Pollable = inputStream.subscribe()
                with pollable: 
                    pollable.block()
                    chunk: bytes = inputStream.read(chunk_size) # All data read here is kept in memory and does not get released
                    yield chunk
            except ...

Is this a bug, or am I missing something in how these resources should be managed?

Thanks in advance for any help!

[dicej]

Thanks for reporting this, @teebee64. It looks like you're doing the right thing using with blocks to manage the resource lifetimes, so it's not immediately obvious what's wrong.

I'll admit I haven't tested componentize-py-generated components much in long-lived scenarios; it ought to work, though. I'll do some profiling to identify the leak(s) and let you know what I find. That might need to wait until later this week; I'm just back from vacation and need to catch up on a few things.

[dicej]

This should be fixed as of version 0.17.1. Let me know if you still have issues.

[teebee64]

Thanks for the fix, the memory issue when reading from a stream looks resolved in 0.17.1.

However, I'm still seeing memory growth when creating OutgoingRequest instances. For example:

with OutgoingRequest(Fields.from_list([])) as outgoingRequest:
    outgoingRequest.set_method(Method_Get())
    outgoingRequest.set_scheme(Scheme_Https())
    ...

It seems memory for these resources isn't being released.

[dicej]

Would be able to provide a test case that reproduces the problem?

[teebee64]

from wit_world import exports
from wit_world.imports.wasi_http_types import Fields, OutgoingRequest, Method_Get, Scheme_Https

class Run(exports.Run):
    def run(self) -> None:
        while True:
            with OutgoingRequest(Fields.from_list([])) as outgoingRequest:
                outgoingRequest.set_method(Method_Get())
                outgoingRequest.set_scheme(Scheme_Https())

This is obviously a tight loop, but it mirrors what happens in my pipeline where I create many OutgoingRequest instances over time. Memory usage keeps increasing steadily, suggesting the resources aren't being fully cleaned up.

[dicej]

Thanks; I'll investigate when I get a chance.