fork and file descriptor

From: Jacky Cheung (jackylb_at_yahoo.com)
Date: 03/08/05 

Date: Tue, 08 Mar 2005 11:39:54 +0800

Hi all,

My program has a main loop and a thread.

The main loop is used to fork a child and the thread is used write data
to dsp.

However I find that there is a cases when the thread opened the dsp, and
at that time the main loop fork a child out. This made the child has the
fd of dsp. So I am thinking to use mutex to make sure dsp is opened in
the child.

Here is my way:

Thread:

mutex lock
        open dsp
        write data to dsp
        close dsp
mutex unlock

main loop:

mutex lock
        if((child_pid=fork())<0){
                DEBUG(0, "fork error \n");
        }else if(child_pid==0){ //child
                //do sth here
        }else{ //parent
mutex unlock
        }

Is it the right location to place the mutex unlock under the parent
process in the main loop? Also does the child need to hanlde the mutex lock?

Thx a lot.

Jacky

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