[PATCHv5/RFC 17/17] gitweb: Add startup delay to activity indicator for cache

[Jakub Narebski <jnareb@gmail.com>]

This adds support for [optional] startup delay to git_generating_data_html()
subroutine, which is used to provide "Generating..." page as activity
indicator when waiting for page to be generated if caching.  If the data
(page contents) gets generated within $generating_options{'staryp_delay'}
seconds, the "Generating..." page won't get displayed.

This feature was created in response to complaint by Petr 'Pasky' Baudis'
about "Generating..." feature.

Signed-off-by: Jakub Narebski <jnareb@gmail.com>
---
No changes since v4 (previous version).

This patch doesn't have equivalent in J.H. patch, and is rather
extension of idea of progress indicator for (re)generating [cache]
data.  It was inspired by comment by Petr 'Pasky' Baudis on #git IRC
channel that one doesn't want to have "Generating..." page to be shown
only to immediately vanish.

 gitweb/gitweb.perl |   20 ++++++++++++++++++++
 1 files changed, 20 insertions(+), 0 deletions(-)

diff --git a/gitweb/gitweb.perl b/gitweb/gitweb.perl
index 07fa825..fee8739 100755
--- a/gitweb/gitweb.perl
+++ b/gitweb/gitweb.perl
@@ -354,6 +354,9 @@ our %cache_options = (
 # (which means that $cache_options{'generating_info'} is set to coderef);
 # override them with $GITWEB_CONFIG as necessary.
 our %generating_options = (
+	# The delay before displaying "Generating..." page, in seconds.  It is
+	# intended for "Generating..." page to be shown only when really needed.
+	'startup_delay' => 1,
 	# The time between generating new piece of output to prevent from
 	# redirection before data is ready, i.e. time between printing each
 	# dot in activity indicator / progress info, in seconds.
@@ -3570,6 +3573,23 @@ sub git_generating_data_html {
 		return;
 	}
 
+	# Initial delay
+	if ($generating_options{'startup_delay'} > 0) {
+		eval {
+			local $SIG{ALRM} = sub { die "alarm clock restart\n" }; # NB: \n required
+			alarm $generating_options{'startup_delay'};
+			flock($lock_fh, LOCK_SH); # blocking readers lock
+			alarm 0;
+		};
+		if ($@) {
+			# propagate unexpected errors
+			die $@ if $@ !~ /alarm clock restart/;
+		} else {
+			# we got response within 'startup_delay' timeout
+			return;
+		}
+	}
+
 	my $title = "[Generating...] " . get_page_title();
 	# TODO: the following line of code duplicates the one
 	# in git_header_html, and it should probably be refactored.
-- 
1.7.3