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PROCESS ID and LOCKING a file...In C??

Posted on 1998-05-22
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Last Modified: 2013-12-25
I have used Perl for some time now allowing my C skills to wither away.  Perl has given me options like
getting the presently launched perl program's process id with the constant variable $$.  This gives me a unique number which I can identify this launched program as (unique from the many that can be launched at one time on a multitasking OS).  Perl also allows me to use a command called FLOCK which will lock a file from being written over by someone else giving exclusive rights to whoever.  

Those commands are great but I need them for C. I am translating my Perl code and really need to know how to get the PROCESS ID for my launched compiled C program. I also need to LOCK a file so that the launched program can have exclusive rights to a file.  And all this in ANSI-C because I want it to work on any platform (Unix/NT) that I compile it for.  

Can you please help me identify these commands in ANSI-C?  Or possibly give me alternative methods to use.  Thank you VERY much!!
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Question by:ljaques
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by:julio011597
ID: 1828848
There isn't an *ANSI-C* way to do the job. That is, you need OS dependent code.
To make your code portable, try to use compiler conditionals.

HTH, julio
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by:WileyKat
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I agree with julio. You need OS-dependant code. What OS are you going to run the code on?
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jhurst earned 100 total points
ID: 1828850
They are right that there is no specific call in ANSI-C however there is a sort of kludge way of getting something uique, actually a PID.  WHat you do is use fork() which as you will find in the manual makes a second copy of the running process and returns the pid to one cope and 0 to the other.  Just have the copy that gets a pid back use this number.  It is a real pid so it gives you what you want.

The lock is more of a problem.  The way that I have always handled this is to make a lock file with the pid when I start and have it removed by the atexit().  Then I just check that there are no other ones there when I start.
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by:ozo
ID: 1828851
getpid is POSIX standard, and should be at least as portable as fork.

The lock file method suggested above can be tricky.
What if another process makes a lock file right after you check that there are no other ones there, and before you make yours?

I'd suggest looking at the perl flock code to see how they emulate it on various different platforms.
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