NAME

File::Flock::Retry - Yet another flock module

VERSION

This document describes version 0.631 of File::Flock::Retry (from Perl distribution File-Flock-Retry), released on 2019-03-12.

SYNOPSIS

 use File::Flock::Retry;

 # try to acquire exclusive lock. if fail to acquire lock within 60s, die.
 my $lock = File::Flock::Retry->lock($file);

 # explicitly unlock
 $lock->release;

 # automatically unlock if object is DESTROY-ed.
 undef $lock;

DESCRIPTION

This is yet another flock module. It is a more lightweight alternative to File::Flock with some other differences:

  • OO interface only

  • Autoretry (by default for 60s) when trying to acquire lock

    I prefer this approach to blocking/waiting indefinitely or failing immediately.

CAVEATS

Not yet tested on Windows. Some filesystems do not support inode?

METHODS

lock

Usage:

 $lock = File::Flock::Retry->lock($path, \%opts)

Attempt to acquire an exclusive lock on $path. By default, $path will be created if not already exists (see "mode"). If $path is already locked by another process, will retry every second for a number of seconds (by default 60). Will die if failed to acquire lock after all retries.

Will automatically unlock if $lock goes out of scope. Upon unlock, will remove $path if it was created by "lock" and is still empty (this behavior is the same as File::Flock).

Available options:

  • mode

    Integer. Default: O_CREAT | O_RDWR.

    File open mode, to be passed to Perl's sysopen(). For example, if you want to avoid race condition between creating and locking the file, you might want to use O_CREAT | O_EXCL | O_RDWR to fail when the file already exists. Note that the constants are available after you do a use Fcntl ':DEFAULT';.

  • retries

    Integer. Default: 60.

    Number of retries (equals number of seconds, since retry is done every second).

  • shared

    Boolean. Default: 0.

    By default, an exclusive lock (LOCK_EX) is attempted. However, if this option is set to true, a shared lock (LOCK_SH) is attempted.

unlock

Usage:

 $lock->unlock

Unlock. will remove lock file if it was created by "lock" and is still empty (this behavior is the same as File::Flock).

release

Usage:

 $lock->release

Synonym for "unlock".

handle

Usage:

 my $fh = $lock->handle;

Return the file handle.

HOMEPAGE

Please visit the project's homepage at https://metacpan.org/release/File-Flock-Retry.

SOURCE

Source repository is at https://github.com/perlancar/perl-File-Flock-Retry.

BUGS

Please report any bugs or feature requests on the bugtracker website https://rt.cpan.org/Public/Dist/Display.html?Name=File-Flock-Retry

When submitting a bug or request, please include a test-file or a patch to an existing test-file that illustrates the bug or desired feature.

SEE ALSO

File::Flock, a bit too heavy in terms of dependencies and startup overhead, for my taste. It depends on things like File::Slurp and Data::Structure::Util (which loads Digest::MD5, Storable, among others).

File::Flock::Tiny which is also tiny, but does not have the autoremove and autoretry capability which I want. See also: https://github.com/trinitum/perl-File-Flock-Tiny/issues/1

flock() Perl function.

An alternative to flock() is just using sysopen() with O_CREAT|O_EXCL mode to create lock files. This is supported on more filesystems (particularly network filesystems which lack flock()).

AUTHOR

perlancar <perlancar@cpan.org>

COPYRIGHT AND LICENSE

This software is copyright (c) 2019, 2017, 2015, 2014 by perlancar@cpan.org.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.