# Multithreading in Different Directories

**URL:** <https://www.ruby-forum.com/t/multithreading-in-different-directories/137680>\
**Category:** Rails\
**Created:** [May 15, 2008, 9:22am UTC](https://www.ruby-forum.com/t/multithreading-in-different-directories/137680 "2008-05-15T09:22:31Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![paerez](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/5fc32e/32.png) [@paerez](https://www.ruby-forum.com/u/paerez)\
**Post date:** [May 15, 2008, 9:22am UTC](https://www.ruby-forum.com/t/multithreading-in-different-directories/137680/1 "2008-05-15T09:22:31Z")

</div>

Hello Everyone,

First message out here on the group, and I hope you can help me out.

I am running a bunch of commands that can take a long time (10 seconds  
to 15  
minutes and beyond). Naturally, I decided to multithread them, which  
makes  
them run a lot faster since I have a multi-core machine. The problem is  
they  
all access a log file in the current directory, and they collide.

So, my next step was to use Dir.chdir to move to another directory for  
each  
thread and run there. Now it works.

Now, my problem is that I have been using backticks (`) to run commands,  
and  
I would like to switch to popen in order to stifle the output (it spits  
out  
a lot of info that I don’t want all over my tests, and it generates odd  
characters that mess up my terminal).

The problem is that popen doesn’t respect Dir.chdir. I have also tried  
things like:

popen(“cd otherdir; command”)  
and  
popen(“cd otherdir && command”)

but it doesn’t seem to care at all, and always runs in rails root.

So I need one of two things:

1. Change directory for popen
2. Stifle stdout and stderr for `command`

Thanks,  
Nick

---

<div class="post-metadata">

**Author:** ![paerez](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/5fc32e/32.png) [@paerez](https://www.ruby-forum.com/u/paerez)\
**Post date:** [May 15, 2008, 6:35pm UTC](https://www.ruby-forum.com/t/multithreading-in-different-directories/137680/2 "2008-05-15T18:35:57Z")

</div>

Thanks for your help.

Clever N. wrote:

> On May 14, 4:27 pm, “Nick Gauthier” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:
> 
> > So, my next step was to use Dir.chdir to move to another directory for each  
> > thread and run there. Now it works.
> 
> This is kind of hackish. Are you sure the binary does not have a  
> switch or option to change where the log file goes? Almost all the  
> standard Unix utils that have logfiles let you modify this. If you  
> have access to the source, adding such a flag is trivial. If the flag  
> exists, simply appending a “random number” (I use the unix timestamp  
> plus another counter (just in case I start two thread in the same  
> second) myself quite often) to a common log name will usually  
> suffice. This is also handy because you can then pull the date and  
> time it was executed from the log file’s name, if you don’t need a  
> running log with detailed timestamps.

I know it’s hackish ☹

The reason I can’t use a switch for the log file is that the program I  
am calling (which does have a log file switch) calls another program  
(which has a log file switch). But, the first program does not have a  
log file switch for the second program’s log file.

> > So I need one of two things:
> > 
> > 1. Change directory for popen
> > 2. Stifle stdout and stderr for `command`
> 
> 2 is easy. The backtick style of calling commands actually spawns a  
> shell, so shell-based redirects to /dev/null (as well as file  
> globbing, scripting, conditional execution, etc.) work as if you were  
> actually at your command line.

I tried piping the output using \>, but I didn’t realize my program was  
actually outputting to stderr, so I just changed it to be 2\> /dev/null  
and now its nice and quiet.

Thanks!

---

<div class="post-metadata">

**Author:** ![paerez](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/5fc32e/32.png) [@paerez](https://www.ruby-forum.com/u/paerez)\
**Post date:** [May 15, 2008, 6:30pm UTC](https://www.ruby-forum.com/t/multithreading-in-different-directories/137680/3 "2008-05-15T18:30:34Z")

</div>

On May 14, 4:27 pm, “Nick Gauthier” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> So, my next step was to use Dir.chdir to move to another directory for each  
> thread and run there. Now it works.

This is kind of hackish. Are you sure the binary does not have a  
switch or option to change where the log file goes? Almost all the  
standard Unix utils that have logfiles let you modify this. If you  
have access to the source, adding such a flag is trivial. If the flag  
exists, simply appending a “random number” (I use the unix timestamp  
plus another counter (just in case I start two thread in the same  
second) myself quite often) to a common log name will usually  
suffice. This is also handy because you can then pull the date and  
time it was executed from the log file’s name, if you don’t need a  
running log with detailed timestamps.

> So I need one of two things:
> 
> 1. Change directory for popen
> 2. Stifle stdout and stderr for `command`

2 is easy. The backtick style of calling commands actually spawns a  
shell, so shell-based redirects to /dev/null (as well as file  
globbing, scripting, conditional execution, etc.) work as if you were  
actually at your command line.