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

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

[Kyle McKay]

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

Signed-off-by: Kyle J. McKay <mackyle@gmail.com>
---
perl/Git.pm | 17 ++++++++++++++++-
1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/perl/Git.pm b/perl/Git.pm
index 7a252ef..5416b5a 100644
--- a/perl/Git.pm
+++ b/perl/Git.pm
@@ -61,7 +61,7 @@ require Exporter;
                 remote_refs prompt
                 get_tz_offset
                 credential credential_read credential_write
-                temp_acquire temp_release temp_reset temp_path);
+                temp_acquire temp_is_locked temp_release temp_reset  
temp_path);


=head1 DESCRIPTION
@@ -1206,6 +1206,21 @@ sub temp_acquire {
	$temp_fd;
}

+=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.
+
+=cut
+
+sub temp_is_locked {
+	my ($self, $name) = _maybe_self(@_);
+	my $temp_fd = \$TEMP_FILEMAP{$name};
+	defined $$temp_fd && $$temp_fd->opened && $TEMP_FILES{$$temp_fd} 
{locked};
+}
+
=item temp_release ( NAME )

=item temp_release ( FILEHANDLE )
-- 
1.8.3

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

[Jonathan Nieder]

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.
[...]
> +=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