File::Flock(3pm) User Contributed Perl Documentation File::Flock(3pm)NAME
File::Flock - file locking with flock
SYNOPSIS
use File::Flock;
lock($filename);
lock($filename, 'shared');
lock($filename, undef, 'nonblocking');
lock($filename, 'shared', 'nonblocking');
unlock($filename);
my $lock = new File::Flock '/somefile';
lock_rename($oldfilename, $newfilename)
DESCRIPTION
Lock files using the flock() call. If the file to be locked does not exist, then the file is created. If the file was created then it
will be removed when it is unlocked assuming it's still an empty file.
Locks can be created by new'ing a File::Flock object. Such locks are automatically removed when the object goes out of scope. The
unlock() method may also be used.
lock_rename() is used to tell File::Flock when a file has been renamed (and thus the internal locking data that is stored based on the
filename should be moved to a new name). unlock() the new name rather than the original name.
LICENSE
File::Flock may be used/modified/distibuted on the same terms as perl itself.
AUTHOR
David Muir Sharnoff <muir@idiom.org>
perl v5.10.1 2008-03-28 File::Flock(3pm)
Check Out this Related Man Page
FLOCK(2) BSD System Calls Manual FLOCK(2)NAME
flock -- apply or remove an advisory lock on an open file
SYNOPSIS
#include <sys/file.h>
#define LOCK_SH 1 /* shared lock */
#define LOCK_EX 2 /* exclusive lock */
#define LOCK_NB 4 /* don't block when locking */
#define LOCK_UN 8 /* unlock */
int
flock(int fd, int operation);
DESCRIPTION
Flock() applies or removes an advisory lock on the file associated with the file descriptor fd. A lock is applied by specifying an operation
parameter that is one of LOCK_SH or LOCK_EX with the optional addition of LOCK_NB. To unlock an existing lock operation should be LOCK_UN.
Advisory locks allow cooperating processes to perform consistent operations on files, but do not guarantee consistency (i.e., processes may
still access files without using advisory locks possibly resulting in inconsistencies).
The locking mechanism allows two types of locks: shared locks and exclusive locks. At any time multiple shared locks may be applied to a
file, but at no time are multiple exclusive, or both shared and exclusive, locks allowed simultaneously on a file.
A shared lock may be upgraded to an exclusive lock, and vice versa, simply by specifying the appropriate lock type; this results in the pre-
vious lock being released and the new lock applied (possibly after other processes have gained and released the lock).
Requesting a lock on an object that is already locked normally causes the caller to be blocked until the lock may be acquired. If LOCK_NB is
included in operation, then this will not happen; instead the call will fail and the error EWOULDBLOCK will be returned.
NOTES
Locks are on files, not file descriptors. That is, file descriptors duplicated through dup(2) or fork(2) do not result in multiple instances
of a lock, but rather multiple references to a single lock. If a process holding a lock on a file forks and the child explicitly unlocks the
file, the parent will lose its lock.
Processes blocked awaiting a lock may be awakened by signals.
RETURN VALUES
Zero is returned if the operation was successful; on an error a -1 is returned and an error code is left in the global location errno.
ERRORS
The flock() call fails if:
[EWOULDBLOCK] The file is locked and the LOCK_NB option was specified.
[EBADF] The argument fd is an invalid descriptor.
[EINVAL] The argument fd refers to an object other than a file.
[EOPNOTSUPP] The referenced descriptor is not of the correct type.
SEE ALSO open(2), close(2), dup(2), execve(2), fork(2)HISTORY
The flock() function call appeared in 4.2BSD.
4.2 Berkeley Distribution December 11, 1993 4.2 Berkeley Distribution