From: Eric Wong <e@80x24.org>
Date: Sat, 12 Apr 2014 04:12:47 +0000 (+0000)
Subject: use flock instead of fcntl locking
X-Git-Tag: v0.0.0~14
X-Git-Url: http://git.tremily.us/?p=ssoma-mda.git;a=commitdiff_plain;h=22db06570ae15b2bfc565840ec30b73e555b90f2

use flock instead of fcntl locking

We do not need range locking of fcntl locks, so using flock removes
a dependency, hopefully making us easier-to-install.  Also keep in
mind Ruby (and perhaps other scripting language) supports flock
out-of-the-box as well, so it seems flock is easier to support
although fcntl locks offer superior functionality.
---

diff --git a/Documentation/ssoma_repository.txt b/Documentation/ssoma_repository.txt
index f7b24ad..6c6022f 100644
--- a/Documentation/ssoma_repository.txt
+++ b/Documentation/ssoma_repository.txt
@@ -48,7 +48,7 @@ two).
 
 # LOCKING
 
-fcntl(2) locking exclusively locks the empty $GIT_DIR/ssoma.lock file
+flock(2) locking exclusively locks the empty $GIT_DIR/ssoma.lock file
 for all non-atomic operations.
 
 # EXAMPLE INPUT FLOW (SERVER-SIDE MDA)
@@ -61,7 +61,7 @@ ssoma-mda handles all steps once invoked.
 
 2. Mail transport agent invokes ssoma-mda
 3. reads message via stdin, extracting Message-ID
-4. acquires fcntl lock on $GIT_DIR/ssoma.lock
+4. acquires exclusive flock lock on $GIT_DIR/ssoma.lock
 5. creates or updates the blob of associated 2/38 SHA-1 path
 6. updates the index and commits
 7. releases $GIT_DIR/ssoma.lock
@@ -88,7 +88,7 @@ Special files in $GIT_DIR on the server:
 :  The normal git index (in $GIT_DIR/index) is not used at all as
    there is typically no working tree.
 
-* $GIT_DIR/ssoma.lock - empty file for fcntl(2) locking
+* $GIT_DIR/ssoma.lock - empty file for flock(2) locking
 :  This is necessary to ensure the index and commits are updated
    consistently and multiple processes running MDA do not step on
    each other.
diff --git a/INSTALL b/INSTALL
index d21a5c7..8f0e378 100644
--- a/INSTALL
+++ b/INSTALL
@@ -19,7 +19,6 @@ convenience.
   - Digest::SHA                 perl
   - Email::LocalDelivery        libemail-localdelivery-perl
   - Email::Simple               libemail-simple-perl
-  - File::FcntlLock             libfile-fcntllock-perl
   - File::Path::Expand          libfile-path-expand-perl
   - Net::IMAP::Simple           libnet-imap-simple-perl
 
diff --git a/Makefile.PL b/Makefile.PL
index 7873a54..f500cc0 100644
--- a/Makefile.PL
+++ b/Makefile.PL
@@ -17,7 +17,6 @@ WriteMakefile(
 		'Digest::SHA' => 0,
 		'Email::LocalDelivery' => 0,
 		'Email::Simple' => 0,
-		'File::FcntlLock' => 0,
 		'File::Path::Expand' => 0,
 		'Net::IMAP::Simple' => 0,
 	},
diff --git a/README b/README
index 3aec620..9c8bfac 100644
--- a/README
+++ b/README
@@ -31,7 +31,6 @@ Requirements (server MDA)
 * MTA - postfix is recommended
 * Perl and several modules:
     - Email::Simple
-    - File::FcntlLock
     - Digest::SHA
 
 Hacking
diff --git a/lib/Ssoma/Git.pm b/lib/Ssoma/Git.pm
index 9a9d82f..aa63e1d 100644
--- a/lib/Ssoma/Git.pm
+++ b/lib/Ssoma/Git.pm
@@ -13,9 +13,8 @@ package Ssoma::Git;
 use strict;
 use warnings;
 use File::Path qw/mkpath/;
+use Fcntl qw/:DEFAULT :flock SEEK_END/;
 use IO::Handle;
-use Fcntl;
-use File::FcntlLock;
 use Email::Simple;
 use Digest::SHA qw/sha1_hex/;
 
@@ -50,12 +49,6 @@ sub lockfile { $_[0]->{git_dir} . "/ssoma.lock" }
 sub sync_do {
 	my ($self, $sub) = @_;
 
-	my $fs = File::FcntlLock->new;
-	$fs->l_type(F_WRLCK);
-	$fs->l_type(SEEK_CUR);
-	$fs->l_start(0);
-	$fs->l_len(0);
-
 	my $path = $self->lockfile;
 	my $lock;
 
@@ -66,14 +59,14 @@ sub sync_do {
 		die "failed to open lock $path: $!\n";
 
 	# wait for other processes to be done
-	$fs->lock($lock, F_SETLKW) or die "lock failed: " . $fs->error . "\n";
+	flock($lock, LOCK_EX) or die "lock failed: $!\n";
 
 	# run the sub!
 	my @ret = eval { &$sub };
 	my $err = $@;
 
 	# these would happen anyways, but be explicit so we can detect errors
-	$fs->lock($lock, F_UNLCK) or die "unlock failed: " . $fs->error . "\n";
+	flock($lock, LOCK_UN) or die "unlock failed: $!\n";
 	close $lock or die "close lockfile($path) failed: $!\n";
 
 	die $err if $err;