[PATCH 2/2] emergency: modernize and reduce syscalls

[Eric Wong <e@80x24.org>]

As with LeiToMail, we'll exclusively rely on O_EXCL and EEXIST
instead of "-f" (stat(2)) for file name collision checking.
Furthermore, we can rely on link(2) error handling instead of
using stat(2) to check the result of link(2).

We'll still keep the hostname in these filenames, but memoize it
on a per-instance basis since hostname changes are rare and we
can assume it won't change between "tmp" and "cur".

We'll also start embedding the PID as {"tmp.$$"} into the fiel
name to guard against accidental deletion in child processes,
instead of requiring an extra hash lookup.

Finally, avoid multiple getpid(2) syscalls in internal subs
since glibc no longer caches in getpid(3).

We'll also favor constant comparison of $! against EEXIST for
inlining. and stop doing ->autoflush when we only have a single
print + flush.
---
 lib/PublicInbox/Emergency.pm | 59 +++++++++++++++---------------------
 1 file changed, 24 insertions(+), 35 deletions(-)

diff --git a/lib/PublicInbox/Emergency.pm b/lib/PublicInbox/Emergency.pm
index 67f27bc7..5a1ed1d7 100644
--- a/lib/PublicInbox/Emergency.pm
+++ b/lib/PublicInbox/Emergency.pm
@@ -4,10 +4,11 @@
 # Emergency Maildir delivery for MDA
 package PublicInbox::Emergency;
 use strict;
-use warnings;
+use v5.10.1;
 use Fcntl qw(:DEFAULT SEEK_SET);
 use Sys::Hostname qw(hostname);
-use IO::Handle; # ->flush, ->autoflush
+use IO::Handle; # ->flush
+use Errno qw(EEXIST);
 
 sub new {
 	my ($class, $dir) = @_;
@@ -20,49 +21,43 @@ sub new {
 			die "failed to mkpath($d): $!\n";
 		}
 	}
-	bless { dir => $dir, files => {}, t => 0, cnt => 0, pid => $$ }, $class;
+	bless { dir => $dir, t => 0 }, $class;
 }
 
 sub _fn_in {
-	my ($self, $dir) = @_;
-	my @host = split(/\./, hostname);
+	my ($self, $pid, $dir) = @_;
+	my $host = $self->{short_host} //= (split(/\./, hostname))[0];
 	my $now = time;
+	my $n;
 	if ($self->{t} != $now) {
 		$self->{t} = $now;
-		$self->{cnt} = 0;
+		$n = $self->{cnt} = 0;
 	} else {
-		$self->{cnt}++;
+		$n = ++$self->{cnt};
 	}
-
-	my $f;
-	do {
-		$f = "$self->{dir}/$dir/$self->{t}.$$"."_$self->{cnt}.$host[0]";
-		$self->{cnt}++;
-	} while (-e $f);
-	$f;
+	"$self->{dir}/$dir/$self->{t}.$pid"."_$n.$host";
 }
 
 sub prepare {
 	my ($self, $strref) = @_;
-
-	die "already in transaction: $self->{tmp}" if $self->{tmp};
+	my $pid = $$;
+	my $tmp_key = "tmp.$pid";
+	die "already in transaction: $self->{$tmp_key}" if $self->{$tmp_key};
 	my ($tmp, $fh);
 	do {
-		$tmp = _fn_in($self, 'tmp');
+		$tmp = _fn_in($self, $pid, 'tmp');
 		$! = undef;
-	} while (!sysopen($fh, $tmp, O_CREAT|O_EXCL|O_RDWR) && $!{EEXIST});
+	} while (!sysopen($fh, $tmp, O_CREAT|O_EXCL|O_RDWR) and $! == EEXIST);
 	print $fh $$strref or die "write failed: $!";
 	$fh->flush or die "flush failed: $!";
-	$fh->autoflush(1);
 	$self->{fh} = $fh;
-	$self->{tmp} = $tmp;
+	$self->{$tmp_key} = $tmp;
 }
 
 sub abort {
 	my ($self) = @_;
 	delete $self->{fh};
-	my $tmp = delete $self->{tmp} or return;
-
+	my $tmp = delete $self->{"tmp.$$"} or return;
 	unlink($tmp) or warn "Failed to unlink $tmp: $!";
 	undef;
 }
@@ -77,21 +72,15 @@ sub fh {
 
 sub commit {
 	my ($self) = @_;
-	$$ == $self->{pid} or return; # no-op in forked child
-
+	my $pid = $$;
+	my $tmp = delete $self->{"tmp.$pid"} or return;
 	delete $self->{fh};
-	my $tmp = delete $self->{tmp} or return;
-	my $new;
+	my ($new, $ok);
 	do {
-		$new = _fn_in($self, 'new');
-	} while (!link($tmp, $new) && $!{EEXIST});
-	my @sn = stat($new) or die "stat $new failed: $!";
-	my @st = stat($tmp) or die "stat $tmp failed: $!";
-	if ($st[0] == $sn[0] && $st[1] == $sn[1]) {
-		unlink($tmp) or warn "Failed to unlink $tmp: $!";
-	} else {
-		warn "stat($new) and stat($tmp) differ";
-	}
+		$new = _fn_in($self, $pid, 'new');
+	} while (!($ok = link($tmp, $new)) && $! == EEXIST);
+	die "link($tmp, $new): $!" unless $ok;
+	unlink($tmp) or warn "Failed to unlink $tmp: $!";
 }
 
 sub DESTROY { commit($_[0]) }