gitweb: Load checking

diff --git a/gitweb/gitweb.perl b/gitweb/gitweb.perl
index 7e477af9567cff322d18fc9a1fbfe507732418dc..e2522cc64f50fbf2a740dd7656373a99f9769119 100755 (executable)
--- a/gitweb/gitweb.perl
+++ b/gitweb/gitweb.perl
@@ -221,6 +221,12 @@ BEGIN
        'double'  => 32
 );
 
+# Used to set the maximum load that we will still respond to gitweb queries.
+# If server load exceed this value then return "503 server busy" error.
+# If gitweb cannot determined server load, it is taken to be 0.
+# Leave it undefined (or set to 'undef') to turn off load checking.
+our $maxload = 300;
+
 # You define site-wide feature defaults here; override them with
 # $GITWEB_CONFIG as necessary.
 our %feature = (
@@ -551,12 +557,38 @@ sub filter_snapshot_fmts {
        do $GITWEB_CONFIG_SYSTEM if -e $GITWEB_CONFIG_SYSTEM;
 }
 
+# Get loadavg of system, to compare against $maxload.
+# Currently it requires '/proc/loadavg' present to get loadavg;
+# if it is not present it returns 0, which means no load checking.
+sub get_loadavg {
+       if( -e '/proc/loadavg' ){
+               open my $fd, '<', '/proc/loadavg'
+                       or return 0;
+               my @load = split(/\s+/, scalar <$fd>);
+               close $fd;
+
+               # The first three columns measure CPU and IO utilization of the last one,
+               # five, and 10 minute periods.  The fourth column shows the number of
+               # currently running processes and the total number of processes in the m/n
+               # format.  The last column displays the last process ID used.
+               return $load[0] || 0;
+       }
+       # additional checks for load average should go here for things that don't export
+       # /proc/loadavg
+
+       return 0;
+}
+
 # version of the core git binary
 our $git_version = qx("$GIT" --version) =~ m/git version (.*)$/ ? $1 : "unknown";
 $number_of_git_cmds++;
 
 $projects_list ||= $projectroot;
 
+if (defined $maxload && get_loadavg() > $maxload) {
+       die_error(503, "The load average on the server is too high");
+}
+
 # ======================================================================
 # input validation and dispatch
 
@@ -3328,7 +3360,8 @@ sub git_footer_html {
        }
 
        print qq!<script type="text/javascript" src="$javascript"></script>\n!;
-       if ($action eq 'blame_incremental') {
+       if (defined $action &&
+           $action eq 'blame_incremental') {
                print qq!<script type="text/javascript">\n!.
                      qq!startBlame("!. href(action=>"blame_data", -replay=>1) .qq!",\n!.
                      qq!           "!. href() .qq!");\n!.
@@ -3354,14 +3387,19 @@ sub git_footer_html {
 # 500: The server isn't configured properly, or
 #      an internal error occurred (e.g. failed assertions caused by bugs), or
 #      an unknown error occurred (e.g. the git binary died unexpectedly).
+# 503: The server is currently unavailable (because it is overloaded,
+#      or down for maintenance).  Generally, this is a temporary state.
 sub die_error {
        my $status = shift || 500;
        my $error = shift || "Internal server error";
 
-       my %http_responses = (400 => '400 Bad Request',
-                             403 => '403 Forbidden',
-                             404 => '404 Not Found',
-                             500 => '500 Internal Server Error');
+       my %http_responses = (
+               400 => '400 Bad Request',
+               403 => '403 Forbidden',
+               404 => '404 Not Found',
+               500 => '500 Internal Server Error',
+               503 => '503 Service Unavailable',
+       );
        git_header_html($http_responses{$status});
        print <<EOF;
 <div class="page_body">