NAME

Lucy::Store::Lock - Abstract class representing an interprocess mutex lock.

SYNOPSIS

my $lock = $lock_factory->make_lock(
    name    => 'write',
    timeout => 5000,
);
$lock->obtain or die "can't get lock for " . $lock->get_name;
do_stuff();
$lock->release;

DESCRIPTION

The Lock class produces an interprocess mutex lock. The default subclass uses dot-lock files, but alternative implementations are possible.

Each lock must have a name which is unique per resource to be locked. Each lock also has a “host” id which should be unique per machine; it is used to help clear away stale locks.

CONSTRUCTORS

new

my $lock = Lucy::Store::Lock->new(
    name     => 'commit',     # required
    folder   => $folder,      # required
    host     => $hostname,    # required
    timeout  => 5000,         # default: 0
    interval => 1000,         # default: 100
);

Abstract constructor.

• folder - A Folder.
• name - String identifying the resource to be locked, which must consist solely of characters matching [-_.A-Za-z0-9].
• host - A unique per-machine identifier.
• timeout - Time in milliseconds to keep retrying before abandoning the attempt to obtain() a lock.
• interval - Time in milliseconds between retries.

ABSTRACT METHODS

shared

my $bool = $lock->shared();

Returns true if the Lock is shared, false if the Lock is exclusive.

request

my $bool = $lock->request();

Make one attempt to acquire the lock.

The semantics of request() differ depending on whether shared() returns true. If the Lock is shared(), then request() should not fail if another lock is held against the resource identified by name (though it might fail for other reasons). If it is not shared() – i.e. it’s an exclusive (write) lock – then other locks should cause request() to fail.

Returns: true on success, false on failure (sets the global error object returned by Clownfish->error).

release

$lock->release();

Release the lock.

is_locked

my $bool = $lock->is_locked();

Indicate whether the resource identified by this lock’s name is currently locked.

Returns: true if the resource is locked, false otherwise.

clear_stale

$lock->clear_stale();

Release all locks that meet the following three conditions: the lock name matches, the host id matches, and the process id that the lock was created under no longer identifies an active process.

METHODS

obtain

my $bool = $lock->obtain();

Call request() once per interval until request() returns success or the timeout has been reached.

Returns: true on success, false on failure (sets the global error object returned by Clownfish->error).

INHERITANCE

Lucy::Store::Lock isa Clownfish::Obj.