treewide: reduce $PATH checks for `git' executable HEAD master

Repeatedly checking $PATH for `git' when we need to call it
multiple times in quick succession doesn't seem useful.  So
avoid some expensive stat(2) syscalls to make things less bad
for systems which require expensive CPU vulnerability
mitigations.

This also saves a bunch of memory allocations since we do the
$PATH lookup in pure Perl to avoid doing the uncacheable lookup
in a vfork-ed child.

1 files changed, 16 insertions, 14 deletions

diff --git a/lib/PublicInbox/Git.pm b/lib/PublicInbox/Git.pm
index aea389e8..a9a821ad 100644
--- a/lib/PublicInbox/Git.pm
+++ b/lib/PublicInbox/Git.pm
@@ -10,6 +10,7 @@ package PublicInbox::Git;
 use strict;
 use v5.10.1;
 use parent qw(Exporter PublicInbox::DS);
+use PublicInbox::DS qw(now);
 use autodie qw(socketpair read);
 use POSIX ();
 use Socket qw(AF_UNIX SOCK_STREAM);
@@ -25,7 +26,7 @@ use PublicInbox::SHA qw(sha_all);
 our %HEXLEN2SHA = (40 => 1, 64 => 256);
 our %OFMT2HEXLEN = (sha1 => 40, sha256 => 64);
 our @EXPORT_OK = qw(git_unquote git_quote %HEXLEN2SHA %OFMT2HEXLEN
-                        $ck_unlinked_packs);
+                        $ck_unlinked_packs git_exe);
 our $in_cleanup;
 our $async_warn; # true in read-only daemons
 
@@ -54,7 +55,11 @@ my %ESC_GIT = map { $GIT_ESC{$_} => $_ } keys %GIT_ESC;
 my $EXE_ST = ''; # pack('dd', st_dev, st_ino); # no `q' in some 32-bit builds
 my ($GIT_EXE, $GIT_VER);
 
-sub check_git_exe () {
+sub git_exe () {
+        my $now = now;
+        state $next_check = $now - 10;
+        return $GIT_EXE if $now < $next_check;
+        $next_check = $now + 10;
         $GIT_EXE = which('git') // die "git not found in $ENV{PATH}";
         my @st = stat(_) or die "stat($GIT_EXE): $!"; # can't do HiRes w/ _
         my $st = pack('dd', $st[0], $st[1]);
@@ -69,8 +74,8 @@ sub check_git_exe () {
         $GIT_EXE;
 }
 
-sub git_version {
-        check_git_exe();
+sub git_version () {
+        git_exe;
         $GIT_VER;
 }
 
@@ -174,7 +179,7 @@ sub _sock_cmd {
 
         # git 2.31.0+ supports -c core.abbrev=no, don't bother with
         # core.abbrev=64 since not many releases had SHA-256 prior to 2.31
-        my $abbr = $GIT_VER lt v2.31.0 ? 40 : 'no';
+        my $abbr = git_version lt v2.31.0 ? 40 : 'no';
         my @cmd = ($GIT_EXE, "--git-dir=$gd", '-c', "core.abbrev=$abbr",
                         'cat-file', "--$batch");
         if ($err_c) {
@@ -287,8 +292,7 @@ sub cat_async_wait ($) {
 
 sub batch_prepare ($) {
         my ($self) = @_;
-        check_git_exe();
-        if ($GIT_VER ge BATCH_CMD_VER) {
+        if (git_version ge BATCH_CMD_VER) {
                 $self->{-bc} = 1;
                 _sock_cmd($self, 'batch-command', 1);
         } else {
@@ -344,8 +348,7 @@ sub ck {
 sub check_async_begin ($) {
         my ($self) = @_;
         cleanup($self) if alternates_changed($self);
-        check_git_exe();
-        if ($GIT_VER ge BATCH_CMD_VER) {
+        if (git_version ge BATCH_CMD_VER) {
                 $self->{-bc} = 1;
                 _sock_cmd($self, 'batch-command', 1);
         } else {
@@ -421,15 +424,15 @@ sub async_err ($$$$$) {
 
 sub cmd {
         my $self = shift;
-        [ $GIT_EXE // check_git_exe(), "--git-dir=$self->{git_dir}", @_ ]
+        [ git_exe(), "--git-dir=$self->{git_dir}", @_ ]
 }
 
 # $git->popen(qw(show f00)); # or
 # $git->popen(qw(show f00), { GIT_CONFIG => ... }, { 2 => ... });
 sub popen {
         my ($self, $cmd) = splice(@_, 0, 2);
-        $cmd = [ 'git', "--git-dir=$self->{git_dir}",
-                ref($cmd) ? @$cmd : ($cmd, grep { defined && !ref } @_) ];
+        $cmd = $self->cmd(ref($cmd) ? @$cmd :
+                        ($cmd, grep { defined && !ref } @_));
         popen_rd($cmd, grep { !defined || ref } @_); # env and opt
 }
 
@@ -577,9 +580,8 @@ sub cloneurl {
 # templates/this--description in git.git
 sub manifest_entry {
         my ($self, $epoch, $default_desc) = @_;
-        check_git_exe();
         my $gd = $self->{git_dir};
-        my @git = ($GIT_EXE, "--git-dir=$gd");
+        my @git = (git_exe, "--git-dir=$gd");
         my $sr = popen_rd([@git, 'show-ref']);
         my $own = popen_rd([@git, qw(config gitweb.owner)]);
         my $mod = popen_rd([@git, @MODIFIED_DATE]);