Re: [PATCH 1/2] Git.pm: add new temp_is_locked function

From: Jonathan Nieder <jrnieder@gmail.com>
Date: Jul 7, 2013, 00:11 UTC
Message-ID: <20130707001148.GD30132@google.com>
In-Reply-To: <D34E9C76-89B8-44E6-B364-C71B2FC2AC52@gmail.com>

Hi,

Kyle McKay wrote:

> The temp_is_locked function can be used to determine whether
> or not a given name previously passed to temp_acquire is
> currently locked.

[...]

Show 7 quoted lines

> +=item temp_is_locked ( NAME )
> +
> +Returns true if the file mapped to C<NAME> is currently locked.
> +
> +If true is returned, an attempt to C<temp_acquire()> the same
> C<NAME> will
> +throw an error.

Looks like this was line-wrapped somewhere in transit.

More importantly, it's not obvious from the above description what this function will do. What is a typical value of NAME? Is it a filename, an arbitrary string, a reference, or something else? Is this a way of checking if a file is flocked? What is a typical way to use this function?

Looking more closely, it looks like this is factoring out the idiom for checking if a name is already in use from the _temp_cache function. Would it make sense for _temp_cache to call this helper?

When is a caller expected to call this function? What guarantees can the caller rely on? After a call to temp_acquire(NAME), will temp_is_locked(NAME) always return true until temp_release(NAME) is called? Does this only work within the context of a single process or can locks persist beyond a process lifetime? Do locks ever need to be broken?

I didn't spend a lot of time trying to find the answers to these questions because I want to make sure that people using Git.pm in the future similarly do not have to spend a lot of time. So hopefully a documentation change could fix this.

Thanks and hope that helps, Jonathan