# Non-blocking IO & Maxima

**URL:** <https://www.ruby-forum.com/t/non-blocking-io-maxima/107611>\
**Category:** Ruby\
**Created:** [June 24, 2007, 12:11am UTC](https://www.ruby-forum.com/t/non-blocking-io-maxima/107611 "2007-06-24T00:11:57Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![mindtriggerz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/4491bb/32.png) [@mindtriggerz](https://www.ruby-forum.com/u/mindtriggerz)\
**Post date:** [June 24, 2007, 12:11am UTC](https://www.ruby-forum.com/t/non-blocking-io-maxima/107611/1 "2007-06-24T00:11:57Z")

</div>

Ok, here’s something that seems wierd. While writing some code to call  
Maxima  
([http://maxima.sourceforge.net/](http://maxima.sourceforge.net/)) from Ruby, I wrote the following:

class IO

# Read a line without blocking. If there isn’t a line to be read,

return

# nil.

def readline\_nonblock  
line = ‘’

```
begin
  char = read_nonblock 1 # A larger read would surely be more 

```

efficient.  
while char != “\n”  
line += char  
char = read\_nonblock 1  
end  
rescue Errno::EAGAIN  
$stderr.puts ‘\*\*\* rescued EAGAIN’  
line.reverse.each\_byte { |c| ungetc(c) } # Replace partial line.  
line = nil  
rescue EOFError  
line = nil  
end

```
line

```

end

# Yield once for every line recieved from readline\_nonblocking, until

it

# returns nil.

def each\_nonblock  
line = readline\_nonblock  
while not line.nil?  
yield line  
line = readline\_nonblock  
end  
end  
end

The wierdness is that this code behaves differently depending on whether  
its  
called from IRB’s toplevel or within a method. Here’s some expected  
results:

irb(main):001:0\> MaximaString = “maxima --batch-string=‘1+1;’”  
=\> “maxima --batch-string=‘1+1;’”  
irb(main):002:0\> ios = IO.popen MaximaString  
=\> #IO:0xb79d6068  
irb(main):003:0\> ios.each\_nonblock { |line| puts line }  
i i i i i i i ooooo o ooooooo ooooo ooooo  
I I I I I I I 8 8 8 8 8 o 8 8  
I \ `+' / I 8 8 8 8 8 8 \ `-±’ / 8 8 8 ooooo 8oooo  
`- **|** -’ 8 8 8 8 8  
| 8 o 8 8 o 8 8  
------±----- ooooo 8oooooo ooo8ooo ooooo 8

## Copyright (c) Bruno Haible, Michael Stoll 1992, 1993 Copyright (c) Bruno Haible, Marcus Daniels 1994-1997 Copyright (c) Bruno Haible, Pierpaolo Bernardi, Sam Steingold 1998 Copyright (c) Bruno Haible, Sam Steingold 1999-2003

Maxima 5.9.1 [http://maxima.sourceforge.net](http://maxima.sourceforge.net)  
Using Lisp CLISP 2.38 (2006-01-24)  
Distributed under the GNU Public License. See the file COPYING.  
Dedicated to the memory of William Schelter.  
This is a development version of Maxima. The function bug\_report()  
provides bug reporting information.  
(%i1) 1 + 1  
(%o1) 2  
=\> nil

And now the unexpected:

irb(main):004:0\> def foo  
irb(main):005:1\> ios = IO.popen MaximaString  
irb(main):006:1\> ios.each\_nonblock { |line| puts line }  
irb(main):007:1\> end  
=\> nil  
irb(main):008:0\> foo  
\*\*\* rescued EAGAIN  
=\> nil

WTF? If I use “ls” instead of “maxima --batch-string=‘1+1;’” then it  
works it  
both cases. So is this a problem with Maxima, Ruby, or my code?

(Oh, and I know that non-blocking IO isn’t required for the specific  
example  
above, but I’d still like it to work to be more general in code I  
haven’t  
posted. And to understand why this is happening.)

---

<div class="post-metadata">

**Author:** ![mindtriggerz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/4491bb/32.png) [@mindtriggerz](https://www.ruby-forum.com/u/mindtriggerz)\
**Post date:** [June 24, 2007, 3:27am UTC](https://www.ruby-forum.com/t/non-blocking-io-maxima/107611/2 "2007-06-24T03:27:13Z")

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In article [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid),  
Jesse M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) writes:

> WTF? If I use “ls” instead of “maxima --batch-string=‘1+1;’” then it works it  
> both cases. So is this a problem with Maxima, Ruby, or my code?

I think it is caused by that maxima is slower than ls.

Try “sleep 1; ls”.

It is impossible to read a line before a line is sent in  
non-blocking manner.

---

<div class="post-metadata">

**Author:** ![mindtriggerz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/4491bb/32.png) [@mindtriggerz](https://www.ruby-forum.com/u/mindtriggerz)\
**Post date:** [June 24, 2007, 2:13pm UTC](https://www.ruby-forum.com/t/non-blocking-io-maxima/107611/3 "2007-06-24T14:13:52Z")

</div>

On Saturday 23 June 2007 21:26, Tanaka A. wrote:

> It is impossible to read a line before a line is sent in  
> non-blocking manner.

Ah, thats it, thanks. I wasn’t thinking about the delay between typing  
lines  
in IRB that gave it the time to execute…