Re: [Chicken-users] Pipe and thread problem

[Felix]

From: Mario Domenech Goulart <address@hidden>
Subject: Re: [Chicken-users] Pipe and thread problem
Date: Wed, 24 Oct 2012 09:44:37 -0400

> Hi Felix,
> 
> On Wed, 24 Oct 2012 08:04:37 -0400 (EDT) Felix <address@hidden> wrote:
> 
>> From: Aaron Patterson <address@hidden>
>> Subject: [Chicken-users] Pipe and thread problem
>> Date: Tue, 23 Oct 2012 14:30:57 -0700
>>
>>> Hi, I'm trying to simulate reading from a TTY that writes every two
>>> seconds.  I want to do this with a pipe and two threads, one thread
>>> writes every N seconds, while the other reads any data available on the
>>> pipe.
>>> 
>>> Unfortunately, my code just hangs.  After speaking with the fine people
>>> in #chicken, it seems that this may be a bug.  We played with different
>>> calls to put the threads to sleep, and different functions to read data,
>>> but they all ended up freezing at some point.
>>
>> The ports obtained from calls to "open-[input|output]-file*" use
>> internally the "stream-port" class (ports on FILE* streams, in this
>> case created via fdopen(3)). These are not thread-aware, AFAICT. Ports
>> created for socket-fd's (tcp.scm) and processes (posixunix.scm, see
>> specifically ##sys#custom-[input|output]-port") apparently do.
> 
> From a user perspective (i.e., without knowing how things are
> implemented by Chicken), how can we know what procedures can be used
> with threads?

Only from the documentation. I'm not sure I understand the question.
It also depends on how likely blocking is.

> 
> Wouldn't such a misuse of I/O operations in the presence of threads be
> a possible cause of #858?

#858 refers to socket ports, which are implemented differently from
the ports that refer to files. Note that spiffy also involves sendfile,
which _does_ non-blocking I/O for files. I think.


cheers,
felix