(This module is modified from Gisle Aas File::CounterFile to use
Interchanges locking protocols lack of fcntl locking was causing
This module implements a persistent counter class. Each counter is
represented by a separate file in the file system. File locking is
applied, so multiple processes might try to access the same counters
at the same time without risk of counter destruction.
You give the file name as the first parameter to the object
constructor (new). The file is created if it does not exist.
If the file name does not start with / or ., then it is
interpreted as a file relative to $Vend::CounterFile::DEFAULT_DIR.
The default value for this variable is initialized from the
environment variable TMPDIR, or /usr/tmp is no environment
variable is defined. You may want to assign a different value to this
variable before creating counters.
If you pass a second parameter to the constructor, that sets the
initial value for a new counter. This parameter only takes effect
when the file is created (i.e. it does not exist before the call).
When you call the inc() method, you increment the counter value by
one. When you call dec() the counter value is decrementd. In both
cases the new value is returned. The dec() method only works for
numerical counters (digits only).
You can peek at the value of the counter (without incrementing it) by
using the value() method.
The counter can be locked and unlocked with the lock() and
unlock() methods. Incrementing and value retrieval is faster when
the counter is locked, because we do not have to update the counter
file all the time. You can query whether the counter is locked with
the locked() method.
There is also an operator overloading interface to the
Vend::CounterFile object. This means that you might use the ++
operator for incrementing the counter, -- operator for decrementing
and you can interpolate counters diretly into strings.