File Locking with fcntl on Darwin Mac OSX Post: 302578027

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Top Forums Shell Programming and Scripting File Locking with fcntl on Darwin Mac OSX Post 302578027 by flagman5 on Wednesday 30th of November 2011 02:18:08 PM

11-30-2011

Registered User

File Locking with fcntl on Darwin Mac OSX

Hello

I have a Perl script that works on non-darwin Mac OS X environments and I think I have narrowed down the issue to a file locking problem.

In other linux environments, the flock struct is defined differently. I have adjusted this via the reference for Mac OS X fcntl(2) man page. The struct is defined as:

Code:

struct flock {
                 off_t       l_start;    /* starting offset */
                 off_t       l_len;      /* len = 0 means until end of file */
                 pid_t       l_pid;      /* lock owner */
                 short       l_type;     /* lock type: read/write, etc. */
                 short       l_whence;   /* type of l_start */
             };

I am using the flock as the following:

Code:

my $msg = fcntl( $LOCKF, F_SETLK, pack("lliss",0,0,0,F_WRLCK,0) ) or die "Something wrong: $!";

The adjustment works on a separate test script that I extracted parts of the script out for testing. However when I deploy it to the real script, it doesnt work anymore. I then did a trial-error sequence and found that after certain 'additions' to the code, anything I add, such as a simple print "hello" statement, would result in the fcntl line not working. (The error outputted is Invalid Argument supplied).

Is it because the offset, len, l_whence are not defined correctly?

Please help. Thanks for your help.

flagman5

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LEARN ABOUT FREEBSD

vop_advlock

VOP_ADVLOCK(9)						   BSD Kernel Developer's Manual					    VOP_ADVLOCK(9)

NAME

     VOP_ADVLOCK -- advisory record locking

SYNOPSIS

     #include <sys/param.h>
     #include <sys/vnode.h>
     #include <sys/fcntl.h>
     #include <sys/lockf.h>

     int
     VOP_ADVLOCK(struct vnode *vp, caddr_t id, int op, struct flock *fl, int flags);

DESCRIPTION

     The arguments are:

     vp     The vnode being manipulated.

     id     The id token which is changing the lock.

     op     The operation to perform (see fcntl(2)).

     fl     Description of the lock.

     flags  One of more of the following:

		  F_RDLCK  Shared or read lock.
		  F_UNLCK  Unlock.
		  F_WRLCK  Exclusive or write lock.
		  F_WAIT   Wait until lock is granted.
		  F_FLOCK  Use flock(2) semantics for lock.
		  F_POSIX  Use POSIX semantics for lock.

     This entry point manipulates advisory record locks on the file.  Most file systems delegate the work for this call to lf_advlock().

RETURN VALUES

     Zero is returned on success, otherwise an error is returned.

SEE ALSO

     fcntl(2), flock(2), vnode(9)

AUTHORS

     This manual page was written by Doug Rabson.

BSD
								   June 30, 1999							       BSD

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