Test t9500 fails if Time::HiRes is missing

Test t9500 fails if Time::HiRes is missing

[Hallvard Breien Furuseth]

t9500-gitweb-standalone-no-errors fails: Git 1.7.9.rc2/1.7.8.4, RHEL
6.2, Perl 5.10.1.  Reverting 3962f1d756ab41c1d180e35483d1c8dffe51e0d1
fixes it.  The commit expects Time::HiRes to be present, but RedHat
has split it out to a separate RPM perl-Time-HiRes.  Better add a
comment about that, so it doesn't get re-reverted.

Or pacify the test and expect gitweb@RHEL-users to install the RPM:

--- git-1.7.9.rc2/t/gitweb-lib.sh~
+++ git-1.7.9.rc2/t/gitweb-lib.sh
@@ -113,4 +113,9 @@
 	test_done
 }
 
+perl -MTime::HiRes -e 0 >/dev/null 2>&1 || {
+	skip_all='skipping gitweb tests, Time::HiRes module not available'
+	test_done
+}
+
 gitweb_init

-- 
Hallvard

Test t9500 fails if Time::HiRes is missing

[Hallvard Breien Furuseth]

I wrote:
> Better add a comment about that, so it doesn't get re-reverted.

Perhaps I should follow my own advise...

> Or pacify the test and expect gitweb@RHEL-users to install the RPM:

--- git-1.7.9.rc2/t/gitweb-lib.sh~
+++ git-1.7.9.rc2/t/gitweb-lib.sh
@@ -113,4 +113,10 @@
 	test_done
 }
 
+# RedHat has moved Time::HiRes out from core Perl to a separate package.
+perl -MTime::HiRes -e 0 >/dev/null 2>&1 || {
+	skip_all='skipping gitweb tests, Time::HiRes module not available'
+	test_done
+}
+
 gitweb_init

-- 
Hallvard

Re: Test t9500 fails if Time::HiRes is missing

[Ævar Arnfjörð Bjarmason]

On Mon, Jan 23, 2012 at 05:50, Hallvard Breien Furuseth
<h.b.furuseth@usit.uio.no> wrote:
> t9500-gitweb-standalone-no-errors fails: Git 1.7.9.rc2/1.7.8.4, RHEL
> 6.2, Perl 5.10.1.  Reverting 3962f1d756ab41c1d180e35483d1c8dffe51e0d1
> fixes it.  The commit expects Time::HiRes to be present, but RedHat
> has split it out to a separate RPM perl-Time-HiRes.  Better add a
> comment about that, so it doesn't get re-reverted.
>
> Or pacify the test and expect gitweb@RHEL-users to install the RPM:
>
> --- git-1.7.9.rc2/t/gitweb-lib.sh~
> +++ git-1.7.9.rc2/t/gitweb-lib.sh
> @@ -113,4 +113,9 @@
>        test_done
>  }
>
> +perl -MTime::HiRes -e 0 >/dev/null 2>&1 || {
> +       skip_all='skipping gitweb tests, Time::HiRes module not available'
> +       test_done
> +}
> +
>  gitweb_init

[Adding Jakub to CC]

This doesn't actually fix the issue, it only sweeps it under the rug
by making the tests pass, gitweb will still fail to compile on Red
Hat once installed.

I think the right solution is to partially revert
3962f1d756ab41c1d180e35483d1c8dffe51e0d1, but add a comment in the
code indicating that it's to deal with RedHat's broken fork of Perl.

However even if it's required in an eval it might still fail at
runtime in the reset_timer() function, which'll need to deal with it
too.

Re: Test t9500 fails if Time::HiRes is missing

[Junio C Hamano]

Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:

> This doesn't actually fix the issue, it only sweeps it under the rug
> by making the tests pass, gitweb will still fail to compile on Red
> Hat once installed.

In the short term for 1.7.9, let's at least warn users about this issue.

-- >8 --
Subject: INSTALL: warn about recent Fedora breakage

Recent releases of Redhat/Fedora are reported to ship Perl binary package
with some core modules stripped away (see http://lwn.net/Articles/477234/)
against the upstream Perl5 people's wishes. The Time::HiRes module used by
gitweb one of them.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---

 * Hopefully, this may resolve itself over time.

 INSTALL |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/INSTALL b/INSTALL
index 8120641..6fa83fe 100644
--- a/INSTALL
+++ b/INSTALL
@@ -83,7 +83,11 @@ Issues of note:
 	- "Perl" version 5.8 or later is needed to use some of the
 	  features (e.g. preparing a partial commit using "git add -i/-p",
 	  interacting with svn repositories with "git svn").  If you can
-	  live without these, use NO_PERL.
+	  live without these, use NO_PERL.  Note that recent releases of
+	  Redhat/Fedora are reported to ship Perl binary package with some
+	  core modules stripped away (see http://lwn.net/Articles/477234/),
+	  so you might need to install additional packages other than Perl
+	  itself, e.g. Time::HiRes.
 
 	- "openssl" library is used by git-imap-send to use IMAP over SSL.
 	  If you don't need it, use NO_OPENSSL.

Re: Test t9500 fails if Time::HiRes is missing

[Jakub Narębski]

On Mon, Jan 23, 2012 at 10:42 AM, Ævar Arnfjörð Bjarmason
<avarab@gmail.com> wrote:
> On Mon, Jan 23, 2012 at 05:50, Hallvard Breien Furuseth <h.b.furuseth@usit.uio.no> wrote:
>>
>> t9500-gitweb-standalone-no-errors fails: Git 1.7.9.rc2/1.7.8.4, RHEL
>> 6.2, Perl 5.10.1.  Reverting 3962f1d756ab41c1d180e35483d1c8dffe51e0d1
>> fixes it.  The commit expects Time::HiRes to be present, but RedHat
>> has split it out to a separate RPM perl-Time-HiRes.  Better add a
>> comment about that, so it doesn't get re-reverted.
>>
>> Or pacify the test and expect gitweb@RHEL-users to install the RPM:
>>
>> --- git-1.7.9.rc2/t/gitweb-lib.sh~
>> +++ git-1.7.9.rc2/t/gitweb-lib.sh
>> @@ -113,4 +113,9 @@
>>        test_done
>>  }
>>
>> +perl -MTime::HiRes -e 0 >/dev/null 2>&1 || {
>> +       skip_all='skipping gitweb tests, Time::HiRes module not available'
>> +       test_done
>> +}
>> +
>>  gitweb_init
>
> [Adding Jakub to CC]
>
> This doesn't actually fix the issue, it only sweeps it under the rug
> by making the tests pass, gitweb will still fail to compile on Red
> Hat once installed.
>
> I think the right solution is to partially revert
> 3962f1d756ab41c1d180e35483d1c8dffe51e0d1, but add a comment in the
> code indicating that it's to deal with RedHat's broken fork of Perl.
>
> However even if it's required in an eval it might still fail at
> runtime in the reset_timer() function, which'll need to deal with it
> too.

I'll try to send a fix today.  Time::HiRes is needed only for optional timing
info.

-- 
Jakub Narebski

Re: Test t9500 fails if Time::HiRes is missing

[Ævar Arnfjörð Bjarmason]

On Fri, Jan 27, 2012 at 06:48, Junio C Hamano <gitster@pobox.com> wrote:
> Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:
>
>> This doesn't actually fix the issue, it only sweeps it under the rug
>> by making the tests pass, gitweb will still fail to compile on Red
>> Hat once installed.
>
> In the short term for 1.7.9, let's at least warn users about this issue.
>
> -- >8 --
> Subject: INSTALL: warn about recent Fedora breakage
>
> Recent releases of Redhat/Fedora are reported to ship Perl binary package
> with some core modules stripped away (see http://lwn.net/Articles/477234/)
> against the upstream Perl5 people's wishes. The Time::HiRes module used by
> gitweb one of them.

Since I wrote that E-Mail I learned what RedHat was doing, I think
that's a far better option. They're splitting up the perl core into
multiple packages, and anyone who has issues with this on RedHat can
trivially just install those packages. So we should just note it in
the INSTALL file as a platform-specific issue and leave it at that.

We *could* deal with this in our code, but I don't think dealing with
every vendor's slightly different perl version is a viable strategy in
the long run.

Re: Test t9500 fails if Time::HiRes is missing

[Hallvard B Furuseth]

 On Mon, 23 Jan 2012 10:42:02 +0100, Ævar Arnfjörð Bjarmason 
 <avarab@gmail.com> wrote:
> On Mon, Jan 23, 2012 at 05:50, Hallvard Breien Furuseth
> <h.b.furuseth@usit.uio.no> wrote:
>> Or pacify the test and expect gitweb@RHEL-users to install the RPM:
>>
>> --- git-1.7.9.rc2/t/gitweb-lib.sh~
>> +++ git-1.7.9.rc2/t/gitweb-lib.sh
>> @@ -113,4 +113,9 @@
>>        test_done
>>  }
>>
>> +perl -MTime::HiRes -e 0 >/dev/null 2>&1 || {
>> +       skip_all='skipping gitweb tests, Time::HiRes module not 
>> available'
>> +       test_done
>> +}
>> +
>>  gitweb_init
>
> [Adding Jakub to CC]
>
> This doesn't actually fix the issue, it only sweeps it under the rug
> by making the tests pass, gitweb will still fail to compile on Red
> Hat once installed.

 Is that relevant?  gitweb-lib.sh already has code to pass the tests if
 Encode, CGI, CGI::Util or CGI::Carp are missing.  I just added another.

-- 
 Hallvard

Re: Test t9500 fails if Time::HiRes is missing

[Jakub Narębski]

On Fri, Jan 27, 2012 at 11:15 AM, Hallvard B Furuseth
<h.b.furuseth@usit.uio.no> wrote:
> On Mon, 23 Jan 2012 10:42:02 +0100, Ævar Arnfjörð Bjarmason
> <avarab@gmail.com> wrote:
>>
>> On Mon, Jan 23, 2012 at 05:50, Hallvard Breien Furuseth
>> <h.b.furuseth@usit.uio.no> wrote:
>>>
>>> Or pacify the test and expect gitweb@RHEL-users to install the RPM:
>>>
>>> --- git-1.7.9.rc2/t/gitweb-lib.sh~
>>> +++ git-1.7.9.rc2/t/gitweb-lib.sh
>>> @@ -113,4 +113,9 @@
>>>        test_done
>>>  }
>>>
>>> +perl -MTime::HiRes -e 0 >/dev/null 2>&1 || {
>>> +       skip_all='skipping gitweb tests, Time::HiRes module not available'
>>> +       test_done
>>> +}
>>> +
>>>  gitweb_init
>>
>>
>> [Adding Jakub to CC]
>>
>> This doesn't actually fix the issue, it only sweeps it under the rug
>> by making the tests pass, gitweb will still fail to compile on Red
>> Hat once installed.
>
>
> Is that relevant?  gitweb-lib.sh already has code to pass the tests if
> Encode, CGI, CGI::Util or CGI::Carp are missing.  I just added another.

The difference is that:
1.) Time::HiRes is a core Perl module, so theoretically it should be always
    installed.
2.) Time::HiRes is not really required for gitweb to work, only for optional
    feature (timing information).

-- 
Jakub Narebski

[PATCH] Revert "gitweb: Time::HiRes is in core for Perl 5.8"

[Jakub Narebski]

On Mon, 23 Jan 2012, Ævar Arnfjörð Bjarmason wrote:
> On Mon, Jan 23, 2012 at 05:50, Hallvard Breien Furuseth <h.b.furuseth@usit.uio.no> wrote:
> >
> > t9500-gitweb-standalone-no-errors fails: Git 1.7.9.rc2/1.7.8.4, RHEL
> > 6.2, Perl 5.10.1.  Reverting 3962f1d756ab41c1d180e35483d1c8dffe51e0d1
> > fixes it.  The commit expects Time::HiRes to be present, but RedHat
> > has split it out to a separate RPM perl-Time-HiRes.  Better add a
> > comment about that, so it doesn't get re-reverted.
> >
> > Or pacify the test and expect gitweb@RHEL-users to install the RPM:
[...]
 
> This doesn't actually fix the issue, it only sweeps it under the rug
> by making the tests pass, gitweb will still fail to compile on Red
> Hat once installed.

I think you meant "fail to run" here.

> I think the right solution is to partially revert
> 3962f1d756ab41c1d180e35483d1c8dffe51e0d1, but add a comment in the
> code indicating that it's to deal with RedHat's broken fork of Perl.

I have added comment in commit message, but not in code.  I wonder if
it would be enough.

> However even if it's required in an eval it might still fail at
> runtime in the reset_timer() function, which'll need to deal with it
> too.

It shouldn't; everything else related to timer is protected with
'if defined $t0', which is false if Time::HiRes module is not available.

Here is the patch
-- >8 --
From: Jakub Narebski <jnareb@gmail.com>
Subject: [PATCH] Revert "gitweb: Time::HiRes is in core for Perl 5.8"

This reverts commit 3962f1d756ab41c1d180e35483d1c8dffe51e0d1.

Though Time::HiRes is a core Perl module, it doesn't necessarily mean
that it is included in 'perl' package, and that it is installed if
Perl is installed.

For example RedHat has split it out to a separate RPM perl-Time-HiRes.

Noticed-by: Hallvard Breien Furuseth <h.b.furuseth@usit.uio.no>
Suggested-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Jakub Narębski <jnareb@gmail.com>
---
 gitweb/gitweb.perl |   12 +++++++-----
 1 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/gitweb/gitweb.perl b/gitweb/gitweb.perl
index abb5a79..c86224a 100755
--- a/gitweb/gitweb.perl
+++ b/gitweb/gitweb.perl
@@ -17,10 +17,12 @@ use Encode;
 use Fcntl ':mode';
 use File::Find qw();
 use File::Basename qw(basename);
-use Time::HiRes qw(gettimeofday tv_interval);
 binmode STDOUT, ':utf8';
 
-our $t0 = [ gettimeofday() ];
+our $t0;
+if (eval { require Time::HiRes; 1; }) {
+	$t0 = [Time::HiRes::gettimeofday()];
+}
 our $number_of_git_cmds = 0;
 
 BEGIN {
@@ -1142,7 +1144,7 @@ sub dispatch {
 }
 
 sub reset_timer {
-	our $t0 = [ gettimeofday() ]
+	our $t0 = [Time::HiRes::gettimeofday()]
 		if defined $t0;
 	our $number_of_git_cmds = 0;
 }
@@ -3974,7 +3976,7 @@ sub git_footer_html {
 		print "<div id=\"generating_info\">\n";
 		print 'This page took '.
 		      '<span id="generating_time" class="time_span">'.
-		      tv_interval($t0, [ gettimeofday() ]).
+		      Time::HiRes::tv_interval($t0, [Time::HiRes::gettimeofday()]).
 		      ' seconds </span>'.
 		      ' and '.
 		      '<span id="generating_cmd">'.
@@ -6253,7 +6255,7 @@ sub git_blame_common {
 		print 'END';
 		if (defined $t0 && gitweb_check_feature('timed')) {
 			print ' '.
-			      tv_interval($t0, [ gettimeofday() ]).
+			      Time::HiRes::tv_interval($t0, [Time::HiRes::gettimeofday()]).
 			      ' '.$number_of_git_cmds;
 		}
 		print "\n";
-- 
1.7.6

Re: [PATCH] Revert "gitweb: Time::HiRes is in core for Perl 5.8"

[Junio C Hamano]

Jakub Narebski <jnareb@gmail.com> writes:

> Though Time::HiRes is a core Perl module, it doesn't necessarily mean
> that it is included in 'perl' package, and that it is installed if
> Perl is installed.

I do not think we have seen the end of Redhat/Fedora Perl saga.  I am
hoping that either one of the two things to happen:

 (1) Redhat/Fedora distrubution reconsiders the situation and fix their
     packages so that by default when its users ask for "Perl" they get
     what the upstream distributes as "Perl" in full, while still allowing
     people who know what they are doing to install a minimum subset
     "perl-base"; or

 (2) Many applications that use and rely on Perl like we do are hit by
     this issue, and Redhat/Fedora users are trained to install the
     perl-full (or whatever it is called) package when applications want
     "Perl".

In other words, I am hoping that "it doesn't necessarily mean" will not
stay true for a long time.  So please hold onto this patch until the dust
settles, and resend it if (1) does not look to be happening in say 3
months.


> For example RedHat has split it out to a separate RPM perl-Time-HiRes.
>
> Noticed-by: Hallvard Breien Furuseth <h.b.furuseth@usit.uio.no>
> Suggested-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
> Signed-off-by: Jakub Narębski <jnareb@gmail.com>
> ---
>  gitweb/gitweb.perl |   12 +++++++-----
>  1 files changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/gitweb/gitweb.perl b/gitweb/gitweb.perl
> index abb5a79..c86224a 100755
> --- a/gitweb/gitweb.perl
> +++ b/gitweb/gitweb.perl
> @@ -17,10 +17,12 @@ use Encode;
>  use Fcntl ':mode';
>  use File::Find qw();
>  use File::Basename qw(basename);
> -use Time::HiRes qw(gettimeofday tv_interval);
>  binmode STDOUT, ':utf8';
>  
> -our $t0 = [ gettimeofday() ];
> +our $t0;
> +if (eval { require Time::HiRes; 1; }) {
> +	$t0 = [Time::HiRes::gettimeofday()];
> +}
>  our $number_of_git_cmds = 0;

Why should these even be initialized here?  Doesn't reset_timer gets
called at the beginning of run_request()?
>  
>  BEGIN {
> @@ -1142,7 +1144,7 @@ sub dispatch {
>  }
>  
>  sub reset_timer {
> -	our $t0 = [ gettimeofday() ]
> +	our $t0 = [Time::HiRes::gettimeofday()]
>  		if defined $t0;
>  	our $number_of_git_cmds = 0;

The statement modifier look ugly.

More importantly, if you are not profiling, i.e. if we didn't initialize
$t0 at the beginning, do you need to reset $number_of_git_cmds at all?

I also think this should take gitweb_check_feature('timed') into
account, perhaps like this:

	sub reset_timer {
        	return unless gitweb_check_feature('timed');
                our $t0 = ...
                our $number_of_git_cmds = 0;
	}

Then all the other

	if (defined $t0 && gitweb_check_feature('timed'))

can become

	if (defined $t0)

If you go this route, even though tee-zero, the beginning of the time, is
a good name for the variable, you may want to rename it to avoid confusing
readers who might take it as a temporary variable #0.

Re: [PATCH] Revert "gitweb: Time::HiRes is in core for Perl 5.8"

[Jakub Narebski]

On Fri, 27 Jan 2012, Junio C Hamano wrote:
> Jakub Narebski <jnareb@gmail.com> writes:
> 
> > Though Time::HiRes is a core Perl module, it doesn't necessarily mean
> > that it is included in 'perl' package, and that it is installed if
> > Perl is installed.
> 
> I do not think we have seen the end of Redhat/Fedora Perl saga.  I am
> hoping that either one of the two things to happen:
> 
>  (1) Redhat/Fedora distrubution reconsiders the situation and fix their
>      packages so that by default when its users ask for "Perl" they get
>      what the upstream distributes as "Perl" in full, while still allowing
>      people who know what they are doing to install a minimum subset
>      "perl-base"; or
> 
>  (2) Many applications that use and rely on Perl like we do are hit by
>      this issue, and Redhat/Fedora users are trained to install the
>      perl-full (or whatever it is called) package when applications want
>      "Perl".
> 
> In other words, I am hoping that "it doesn't necessarily mean" will not
> stay true for a long time.  So please hold onto this patch until the dust
> settles, and resend it if (1) does not look to be happening in say 3
> months.
 
So for the time being (those "3 months") you would apply instead your
change to INSTALL (or equivalent to gitweb/INSTALL) mentioning Time::HiRes
issue, and perhaps also original patch by Hallvard skipping gitweb tests
if Time::HiRes is not available, isn't it?
 
> > For example RedHat has split it out to a separate RPM perl-Time-HiRes.

[...]
> > diff --git a/gitweb/gitweb.perl b/gitweb/gitweb.perl
> > index abb5a79..c86224a 100755
> > --- a/gitweb/gitweb.perl
> > +++ b/gitweb/gitweb.perl
> > @@ -17,10 +17,12 @@ use Encode;
> >  use Fcntl ':mode';
> >  use File::Find qw();
> >  use File::Basename qw(basename);
> > -use Time::HiRes qw(gettimeofday tv_interval);
> >  binmode STDOUT, ':utf8';
> >  
> > -our $t0 = [ gettimeofday() ];
> > +our $t0;
> > +if (eval { require Time::HiRes; 1; }) {
> > +	$t0 = [Time::HiRes::gettimeofday()];
> > +}
> >  our $number_of_git_cmds = 0;
> 
> Why should these even be initialized here?  Doesn't reset_timer gets
> called at the beginning of run_request()?

I think it predates adding reset_timer() to gitweb.  Anyway $t0 has
to be set to something defined anyway to denote that Time::HiRes is
available... though if Time::HiRes is required unconditionally it would
not be really needed, and we can always check $INC{'Time/HiRes.pm'}
if it was loaded or not.

> >  BEGIN {
> > @@ -1142,7 +1144,7 @@ sub dispatch {
> >  }
> >  
> >  sub reset_timer {
> > -	our $t0 = [ gettimeofday() ]
> > +	our $t0 = [Time::HiRes::gettimeofday()]
> >  		if defined $t0;
> >  	our $number_of_git_cmds = 0;
> 
> The statement modifier look ugly.
> 
> More importantly, if you are not profiling, i.e. if we didn't initialize
> $t0 at the beginning, do you need to reset $number_of_git_cmds at all?
> 
> I also think this should take gitweb_check_feature('timed') into
> account, perhaps like this:
> 
> 	sub reset_timer {
>         	return unless gitweb_check_feature('timed');
>                 our $t0 = ...
>                 our $number_of_git_cmds = 0;
> 	}
> 
> Then all the other
> 
> 	if (defined $t0 && gitweb_check_feature('timed'))
> 
> can become
> 
> 	if (defined $t0)

I think this is a good idea... though it would complicate applying revert
a bit ;-(

> If you go this route, even though tee-zero, the beginning of the time, is
> a good name for the variable, you may want to rename it to avoid confusing
> readers who might take it as a temporary variable #0.

Good idea.  $request_start_time perhaps?  Or $time_start?

-- 
Jakub Narebski
Poland

Re: [PATCH] Revert "gitweb: Time::HiRes is in core for Perl 5.8"

[Ævar Arnfjörð Bjarmason]

On Fri, Jan 27, 2012 at 18:45, Jakub Narebski <jnareb@gmail.com> wrote:
> On Mon, 23 Jan 2012, Ævar Arnfjörð Bjarmason wrote:
>> On Mon, Jan 23, 2012 at 05:50, Hallvard Breien Furuseth <h.b.furuseth@usit.uio.no> wrote:
>> >
>> > t9500-gitweb-standalone-no-errors fails: Git 1.7.9.rc2/1.7.8.4, RHEL
>> > 6.2, Perl 5.10.1.  Reverting 3962f1d756ab41c1d180e35483d1c8dffe51e0d1
>> > fixes it.  The commit expects Time::HiRes to be present, but RedHat
>> > has split it out to a separate RPM perl-Time-HiRes.  Better add a
>> > comment about that, so it doesn't get re-reverted.
>> >
>> > Or pacify the test and expect gitweb@RHEL-users to install the RPM:
> [...]
>
>> This doesn't actually fix the issue, it only sweeps it under the rug
>> by making the tests pass, gitweb will still fail to compile on Red
>> Hat once installed.
>
> I think you meant "fail to run" here.

I mean fail to compile, "use" statements are executed at compile time,
if it was a "require" outside of BEGIN-time it would fail at runtime.

I realize though that you probably thought I meant fail in Git's
Makefile-driven compilation phase, but no, it'll install just fine,
however the perl interpreter won't compile it.

>> I think the right solution is to partially revert
>> 3962f1d756ab41c1d180e35483d1c8dffe51e0d1, but add a comment in the
>> code indicating that it's to deal with RedHat's broken fork of Perl.
>
> I have added comment in commit message, but not in code.  I wonder if
> it would be enough.
>
>> However even if it's required in an eval it might still fail at
>> runtime in the reset_timer() function, which'll need to deal with it
>> too.
>
> It shouldn't; everything else related to timer is protected with
> 'if defined $t0', which is false if Time::HiRes module is not available.

Correct, I didn't look carefully enough.

Re: [PATCH] Revert "gitweb: Time::HiRes is in core for Perl 5.8"

[Ævar Arnfjörð Bjarmason]

On Fri, Jan 27, 2012 at 21:44, Junio C Hamano <gitster@pobox.com> wrote:
>
>        if (defined $t0)
>
> If you go this route, even though tee-zero, the beginning of the
> time, is a good name for the variable, you may want to rename it to
> avoid confusing readers who might take it as a temporary variable
> #0.

<trivia>

Personally I'd have written it as $START_TIME, but as a bit of Perl
trivia you might not realize $t0 is a commonly used and undestood
variable for dealing with a start time in Perl in the same way that
`i` is common for dealing with array indexes in C.

I.e. someone used to Perl will immediately think "oh that's the start
time" having seen it hundreds of times before, but someone not used to
Perl will go "what's this t-zero thing?".

Meanwhile some Lisp programmer is wondering what the hell "i" means in
your C for-loops, iterator? :)