From: Robert Klemme <shortcutter@...>
Date: 2010-01-08T03:35:07+09:00
Subject: Re: Non-blocking communication between Ruby processes

On 01/07/2010 06:58 PM, Iñaki Baz Castillo wrote:
> El Jueves, 7 de Enero de 2010, Iñaki Baz Castillo escribió:
>> The doubt I have now is about how secure is a pipe. 
>> Could it leak memory if some process die or the reader process is not so
>>  fast  to handle the received data?
> 
> Hummm, I have a reader process and a writer process.

I thought you have multiple writers.  Didn't you mention multiple forked 
Rack handlers?

> The wirter process writes into the pipe file.
> If I kill the reader process then the writer process remains writting in the 
> pipe and the data is stored (in the filesystem?).
> 
> So there is the leaking problem...

Not exactly: the writer is blocked.  You can try this out:

robert@fussel:~$ mkfifo ff
robert@fussel:~$ ls -lF ff
prw-r--r-- 1 robert robert 0 2010-01-07 19:25 ff|
robert@fussel:~$ ruby19 -e 'puts("+"*10_000)' > ff
^Z
[1]+  Stopped                 ruby19 -e 'puts("+"*10_000)' > ff
robert@fussel:~$ wc ff &
[2] 14036
robert@fussel:~$ %1
ruby19 -e 'puts("+"*10_000)' > ff
robert@fussel:~$       1       1   10001 ff

[2]+  Done                    wc ff
robert@fussel:~$ jobs
robert@fussel:~$

At the point where I pressed Ctrl-Z the writer hung because the pipe was 
full.  (The size of a pipe is usually the memory page size of the OS 
IIRC, this would be 4k in case of Linux 32 bit).

> I must investigate it a bit more...

I'd personally prefer to use the DRb approach because then you can 
actually send typed messages, i.e. whatever information you need.  Also, 
it was fun to play around with those small test programs. ;-)  And you 
can have the reader run on any machine in the network.

Whatever you do, you have to decide how to go about the situation when 
the reader goes away - for whatever reasons.  You could write your 
messages to a file and use an approach like "tail -f" uses to read them. 
  But this has the nasty effect of clobbering the file system plus if 
the reader goes away the file might grow arbitrary large.  And you have 
locking issues.  Using any in memory pipe (e.g. mkfifo or via DRb) is 
preferrable IMHO.  The you can still decide in the client what you do if 
you cannot get rid of the message.

> Thanks a lot.

You're welcome.

Kind regards

	robert

-- 
remember.guy do |as, often| as.you_can - without end
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