StreamReader.read(-1) deadlocks while reading from a pipe

[Akira Li]

Hi,

stream.read() blocks forever when reading from a pipe with data that is larger than 2 * limit.

stream.read(n) for non-negative n doesn't deadlock in this case.

For example, if asyncio.StreamReader(loop=loop) is replaced with

asyncio.StreamReader(loop=loop, limit=(len(b'data') // 2 - 1))

in examples/subprocess_attach_read_pipe.py then

yield from reader.read() never returns.

https://code.google.com/p/tulip/source/browse/examples/subprocess_attach_read_pipe.py

It is reproducible for larger limit values if the data to be send is larger than 2*limit.

I've attached the test file that demonstrates it without an external process.

Is it the correct way to connect a read pipe to the event loop?

Related discussion: 

https://code.google.com/p/tulip/source/detail?r=0a716436176993a12cf861b6cafffe8a31bc1127

[Guido van Rossum]

Hi Akira,

Thanks for reporting this. There definitely is a bug in asyncio here -- I can repro this exactly!

I haven't found a fix yet, but it seems we're not making progress when the protocol is paused.

If I don't get further today I'll file a bug to track this.

--
--Guido van Rossum (python.org/~guido)

[Guido van Rossum]

I've now opened https://code.google.com/p/tulip/issues/detail?id=168 so we have a place to refer to when I have a fix.

[Guido van Rossum]

This is now fixed in the Tulip repo and in the CPython 3.4 and default branches. Akira, thanks for reporting this issue!