Git.pm: Add faculties to allow temp files to be cached
This patch offers a generic interface to allow temp files to be cached while using an instance of the 'Git' package. If many temp files are created and destroyed during the execution of a program, this caching mechanism can help reduce the amount of files created and destroyed by the filesystem. The temp_acquire method provides a weak guarantee that a temp file will not be stolen by subsequent requests. If a file is locked when another acquire request is made, a simple error is thrown. Signed-off-by: Marcus Griep <marcus@griep.us> Acked-by: Eric Wong <normalperson@yhbt.net>
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perl/Git.pm
125
perl/Git.pm
@ -57,7 +57,8 @@ require Exporter;
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command_output_pipe command_input_pipe command_close_pipe
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command_bidi_pipe command_close_bidi_pipe
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version exec_path hash_object git_cmd_try
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remote_refs);
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remote_refs
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temp_acquire temp_release temp_reset);
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=head1 DESCRIPTION
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@ -99,7 +100,9 @@ use Carp qw(carp croak); # but croak is bad - throw instead
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use Error qw(:try);
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use Cwd qw(abs_path);
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use IPC::Open2 qw(open2);
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use File::Temp ();
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require File::Spec;
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use Fcntl qw(SEEK_SET SEEK_CUR);
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}
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@ -933,6 +936,124 @@ sub _close_cat_blob {
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delete @$self{@vars};
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}
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{ # %TEMP_* Lexical Context
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my (%TEMP_LOCKS, %TEMP_FILES);
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=item temp_acquire ( NAME )
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Attempts to retreive the temporary file mapped to the string C<NAME>. If an
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associated temp file has not been created this session or was closed, it is
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created, cached, and set for autoflush and binmode.
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Internally locks the file mapped to C<NAME>. This lock must be released with
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C<temp_release()> when the temp file is no longer needed. Subsequent attempts
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to retrieve temporary files mapped to the same C<NAME> while still locked will
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cause an error. This locking mechanism provides a weak guarantee and is not
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threadsafe. It does provide some error checking to help prevent temp file refs
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writing over one another.
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In general, the L<File::Handle> returned should not be closed by consumers as
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it defeats the purpose of this caching mechanism. If you need to close the temp
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file handle, then you should use L<File::Temp> or another temp file faculty
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directly. If a handle is closed and then requested again, then a warning will
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issue.
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=cut
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sub temp_acquire {
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my ($self, $name) = _maybe_self(@_);
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my $temp_fd = _temp_cache($name);
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$TEMP_LOCKS{$temp_fd} = 1;
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$temp_fd;
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}
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=item temp_release ( NAME )
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=item temp_release ( FILEHANDLE )
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Releases a lock acquired through C<temp_acquire()>. Can be called either with
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the C<NAME> mapping used when acquiring the temp file or with the C<FILEHANDLE>
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referencing a locked temp file.
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Warns if an attempt is made to release a file that is not locked.
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The temp file will be truncated before being released. This can help to reduce
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disk I/O where the system is smart enough to detect the truncation while data
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is in the output buffers. Beware that after the temp file is released and
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truncated, any operations on that file may fail miserably until it is
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re-acquired. All contents are lost between each release and acquire mapped to
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the same string.
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=cut
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sub temp_release {
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my ($self, $temp_fd, $trunc) = _maybe_self(@_);
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if (ref($temp_fd) ne 'File::Temp') {
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$temp_fd = $TEMP_FILES{$temp_fd};
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}
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unless ($TEMP_LOCKS{$temp_fd}) {
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carp "Attempt to release temp file '",
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$temp_fd, "' that has not been locked";
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}
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temp_reset($temp_fd) if $trunc and $temp_fd->opened;
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$TEMP_LOCKS{$temp_fd} = 0;
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undef;
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}
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sub _temp_cache {
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my ($name) = @_;
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my $temp_fd = \$TEMP_FILES{$name};
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if (defined $$temp_fd and $$temp_fd->opened) {
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if ($TEMP_LOCKS{$$temp_fd}) {
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throw Error::Simple("Temp file with moniker '",
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$name, "' already in use");
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}
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} else {
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if (defined $$temp_fd) {
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# then we're here because of a closed handle.
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carp "Temp file '", $name,
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"' was closed. Opening replacement.";
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}
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$$temp_fd = File::Temp->new(
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TEMPLATE => 'Git_XXXXXX',
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DIR => File::Spec->tmpdir
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) or throw Error::Simple("couldn't open new temp file");
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$$temp_fd->autoflush;
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binmode $$temp_fd;
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}
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$$temp_fd;
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}
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=item temp_reset ( FILEHANDLE )
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Truncates and resets the position of the C<FILEHANDLE>.
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=cut
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sub temp_reset {
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my ($self, $temp_fd) = _maybe_self(@_);
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truncate $temp_fd, 0
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or throw Error::Simple("couldn't truncate file");
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sysseek($temp_fd, 0, SEEK_SET) and seek($temp_fd, 0, SEEK_SET)
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or throw Error::Simple("couldn't seek to beginning of file");
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sysseek($temp_fd, 0, SEEK_CUR) == 0 and tell($temp_fd) == 0
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or throw Error::Simple("expected file position to be reset");
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}
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sub END {
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unlink values %TEMP_FILES if %TEMP_FILES;
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}
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} # %TEMP_* Lexical Context
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=back
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=head1 ERROR HANDLING
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