Redirecting STDOUT/STDERR of a process forked by a thread

Hi,

I'm trying to use threads in one of our applications. The application has
few long running jobs which can be done in parallel and I'm thinking
perl-ithreads can be of use here. 
My proto-type implementation does something like this:

1. Open Log main.log
2. Redirect STDOUT and STDERR to main.log
3. <Some processing>
4. Spawn thread #1:
   4a. Open thread.log and redirect fd of main.log to thread.log
   4b. Redirect STDOUT and STDERR to thread.log
   4c. Print few messages to STDOUT, STDERR, fd
   4d. Fork & exec an external program. (Eg. system("ls -l ")

My problem is that all o/p in 4d goes to the main.log. (4c goes to
thread.log) Once a thread is launched, I'd like to have all the o/p go to
thread.log. Once the thread has exited, I'll append thread.log to main.log.

I guess the reason step 4d does not work is this:
* Once a thread is launched, STDOUT/STDERR ..etc. are 'faked' - ie.
fileno(STDOUT) != 1
* When I exec() a program, it's STDOUT = 1, STDERR = 2. So anything that's
printed by the exec'd program goes to main.log.

Has anyone faced similar issues ? Is there anyway I can point STDOUT to fd
1 inside a thread ?
I tried
open(STDOUT, "<&=1") in the thread but got error 'Invalid argument' from
open.

I can post a complete script example if needed.
Appreciate any help.

thanks
Sreeji