lei_mail_sync: rely on flock(2), avoid IPC

Since 44917fdd24a8bec1 ("lei_mail_sync: do not use transactions"),
relying on lei/store to serialize access was a pointless endeavor.

Rely on flock(2) to serialize multiple writers since (in my
experience) it's the easiest way to deal with parallel writers
when using SQLite.  This allows us to simplify existing callers
while speeding up 'lei refresh-mail-sync --all=local' by 5% or
so.

1 files changed, 36 insertions, 10 deletions

diff --git a/lib/PublicInbox/LeiMailSync.pm b/lib/PublicInbox/LeiMailSync.pm
index 8f584ccb..690c6477 100644
--- a/lib/PublicInbox/LeiMailSync.pm
+++ b/lib/PublicInbox/LeiMailSync.pm
@@ -5,6 +5,7 @@
 package PublicInbox::LeiMailSync;
 use strict;
 use v5.10.1;
+use parent qw(PublicInbox::Lock);
 use DBI;
 use PublicInbox::ContentHash qw(git_sha);
 use Carp ();
@@ -21,7 +22,7 @@ sub dbh_new {
                 sqlite_use_immediate_transaction => 1,
         });
         # no sqlite_unicode, here, all strings are binary
-        create_tables($dbh) if $rw;
+        create_tables($self, $dbh) if $rw;
         $dbh->do('PRAGMA journal_mode = WAL') if $creat;
         $dbh->do('PRAGMA case_sensitive_like = ON');
         $dbh;
@@ -29,13 +30,24 @@ sub dbh_new {
 
 sub new {
         my ($cls, $f) = @_;
-        bless { filename => $f, fmap => {} }, $cls;
+        bless {
+                filename => $f,
+                fmap => {},
+                lock_path => "$f.flock",
+        }, $cls;
 }
 
-sub lms_write_prepare { ($_[0]->{dbh} //= dbh_new($_[0], 1)) };
+sub lms_write_prepare { ($_[0]->{dbh} //= dbh_new($_[0], 1)); $_[0] }
+
+sub lms_pause {
+        my ($self) = @_;
+        $self->{fmap} = {};
+        delete $self->{dbh};
+}
 
 sub create_tables {
-        my ($dbh) = @_;
+        my ($self, $dbh) = @_;
+        my $lk = $self->lock_for_scope;
 
         $dbh->do(<<'');
 CREATE TABLE IF NOT EXISTS folders (
@@ -115,8 +127,15 @@ EOM
         $fid;
 }
 
+sub add_folders {
+        my ($self, @folders) = @_;
+        my $lk = $self->lock_for_scope;
+        for my $f (@folders) { $self->{fmap}->{$f} //= fid_for($self, $f, 1) }
+}
+
 sub set_src {
         my ($self, $oidbin, $folder, $id) = @_;
+        my $lk = $self->lock_for_scope;
         my $fid = $self->{fmap}->{$folder} //= fid_for($self, $folder, 1);
         my $sth;
         if (ref($id)) { # scalar name
@@ -134,6 +153,7 @@ INSERT OR IGNORE INTO blob2num (oidbin, fid, uid) VALUES (?, ?, ?)
 
 sub clear_src {
         my ($self, $folder, $id) = @_;
+        my $lk = $self->lock_for_scope;
         my $fid = $self->{fmap}->{$folder} //= fid_for($self, $folder, 1);
         my $sth;
         if (ref($id)) { # scalar name
@@ -152,6 +172,7 @@ DELETE FROM blob2num WHERE fid = ? AND uid = ?
 # Maildir-only
 sub mv_src {
         my ($self, $folder, $oidbin, $id, $newbn) = @_;
+        my $lk = $self->lock_for_scope;
         my $fid = $self->{fmap}->{$folder} //= fid_for($self, $folder, 1);
         my $sth = $self->{dbh}->prepare_cached(<<'');
 UPDATE blob2name SET name = ? WHERE fid = ? AND oidbin = ? AND name = ?
@@ -421,18 +442,23 @@ EOF
         $err;
 }
 
-sub forget_folder {
-        my ($self, $folder) = @_;
-        my $fid = delete($self->{fmap}->{$folder}) //
-                fid_for($self, $folder) // return;
-        for my $t (qw(blob2name blob2num folders)) {
-                $self->{dbh}->do("DELETE FROM $t WHERE fid = ?", undef, $fid);
+sub forget_folders {
+        my ($self, @folders) = @_;
+        my $lk = $self->lock_for_scope;
+        for my $folder (@folders) {
+                my $fid = delete($self->{fmap}->{$folder}) //
+                        fid_for($self, $folder) // next;
+                for my $t (qw(blob2name blob2num folders)) {
+                        $self->{dbh}->do("DELETE FROM $t WHERE fid = ?",
+                                        undef, $fid);
+                }
         }
 }
 
 # only used for changing canonicalization errors
 sub rename_folder {
         my ($self, $old, $new) = @_;
+        my $lk = $self->lock_for_scope;
         my $ofid = delete($self->{fmap}->{$old}) //
                 fid_for($self, $old) // return;
         eval {