Reference

File::Flock::Retry(3pm)

Yet another flock module

NAME

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

VERSION

This document describes version 0.632 of File::Flock::Retry (from Perl distribution File-Flock-Retry), released on 2021-08-10.

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.

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 is still empty (zero-sized).

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 is still empty.

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.

CAVEATS

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

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 <[email protected]>

COPYRIGHT AND LICENSE

This software is copyright (c) 2021, 2019, 2017, 2015, 2014 by perlancar <[email protected]>.

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

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