Experiment with a singleton version for imgsrv.

Dockerfile

@@ -161,7 +161,8 @@ RUN cpan \
   Test::Exception \
   Devel::Cycle \
   Test::Memory::Cycle \
-  Mozilla::CA
+  Mozilla::CA \
+  Prometheus::Tiny::Shared
 
 RUN mkdir /htapps
 RUN mkdir /htapps/babel

MdpItem.pm

@@ -34,6 +34,7 @@ use Context;
 use Auth::Auth;
 use Identifier;
 use MarcMetadata;
+use Metrics;
 use MetsReadingOrder;
 use DataTypes;
 
@@ -291,10 +292,8 @@ sub GetMdpItem {
     }
 
     my $delta = Time::HiRes::time() - $time0;
-    if(my $metrics = $C->{Metrics}) {
-      $mdpItem->{_metrics} = $C->{Metrics};
-      $metrics->observe("mdpitem_get_mdpitem_seconds",$delta, { cache => $cache_status });
-    }
+
+    Metrics->new->observe("mdpitem_get_mdpitem_seconds", $delta, { cache => $cache_status });
     Utils::Logger::__Log_benchmark($C, 
         [["id", $id],["delta",$delta],["label","GetMdpItem"],["cache",$cache_status]], 'mdpitem');
 
@@ -1838,7 +1837,6 @@ sub GetDirPathMaybeExtract {
                  $fileSystemLocation,
                  $pattern_arr_ref,
                  $exclude_pattern_arr_ref,
-                 $self->{_metrics}
                 );
     }
     else
@@ -1893,9 +1891,7 @@ sub GetFilePathMaybeExtract {
                  $self->GetId(),
                  $fileSystemLocation,
                  $fileName,
-                 $suffix,
-                 undef,
-                 $self->{_metrics}
+                 $suffix
                 );
     }
     else

Metrics.pm

@@ -0,0 +1,59 @@
+package Metrics;
+
+use Prometheus::Tiny::Shared;
+
+my $singleton = undef;
+
+sub new {
+  # Re-use singleton if defined.
+  if (!defined $singleton) {
+    my $class = shift;
+    my $self  = {};
+
+    $self->{prom} = Prometheus::Tiny::Shared->new(
+      #filename => $self->{file}
+    );
+    $self->{declared_metrics} = {};
+    $singleton = bless($self, $class);
+  }
+  return $singleton;
+}
+
+sub declare {
+  my $self   = shift;
+  my $metric = shift;
+
+  $self->{declared_metrics}->{$metric} = 1;
+  $self->{prom}->declare($metric, @_);
+}
+
+sub is_declared {
+  my $self   = shift;
+  my $metric = shift;
+
+  defined $self->{declared_metrics}->{$metric};
+}
+
+sub observe {
+  my $self   = shift;
+  my $metric = shift;
+
+  return unless $self->is_declared($metric);
+  $self->{prom}->histogram_observe($metric, @_);
+}
+
+sub add {
+  my $self = shift;
+  my $metric = shift;
+
+  return unless $self->is_declared($metric);
+  $self->{prom}->add($metric, @_);
+}
+
+sub format {
+  my $self = shift;
+
+  $self->{prom}->format;
+}
+
+1;

Utils/Extract.pm

@@ -26,6 +26,7 @@ use Utils::Logger;
 use Utils::MonitorRun;
 use Identifier;
 use Debug::DUtils;
+use Metrics;
 use Utils::Logger;
 
 # Perl
@@ -204,10 +205,9 @@ sub extract_file_to_temp_cache {
     my @unzip;
     push @unzip, $UNZIP_PROG, "-j", "-qq", "-d", $input_cache_dir, $zip_file, "$stripped_pairtree_id/$filename";
 
-    __run(id => $id, 
-      unzip => \@unzip, 
-      test_filename => "$input_cache_dir/$filename", 
-      metrics => $metrics);
+    __run(id => $id,
+      unzip => \@unzip,
+      test_filename => "$input_cache_dir/$filename");
 
     return
       (-e qq{$input_cache_dir/$filename})
@@ -292,7 +292,6 @@ sub extract_dir_to_temp_cache {
     my $file_sys_location = shift;
     my $patterns_arr_ref = shift;
     my $exclude_patterns_arr_ref = shift;
-    my $metrics = shift;
 
     my $stripped_pairtree_id = Identifier::get_pairtree_id_wo_namespace($id);
     my $zip_file = $file_sys_location . qq{/$stripped_pairtree_id.zip};
@@ -307,7 +306,7 @@ sub extract_dir_to_temp_cache {
         push @unzip, "-x", @$exclude_patterns_arr_ref;
     }
 
-    __run(id => $id, unzip => \@unzip, metrics => $metrics);
+    __run(id => $id, unzip => \@unzip);
 
     return $input_cache_dir;
 }
@@ -317,7 +316,6 @@ sub __run {
     my $id = $params{id};
     my $unzip = $params{unzip};
     my $test_filename = $params{test_filename};
-    my $metrics = $params{metrics};
 
     my $error_file = Utils::get_tmp_logdir() . '/extract-error';
 
@@ -350,9 +348,9 @@ sub __run {
     my $delta = Time::HiRes::time() - $time0;
     # TODO: Add io stats to __Log_benchmark output?
     Utils::Logger::__Log_benchmark(undef, [["id", $id],["delta",$delta],["label","__run"],["cmd",$cmd]], 'extract');
-
-    if($metrics and $test_filename) {
-      $metrics->observe("utils_extract_run_seconds",$delta);
+    if ($test_filename) {
+      my $metrics = Metrics->new;
+      $metrics->observe("utils_extract_run_seconds", $delta);
       # TODO add extracted size when extracting more than one file?
       $metrics->add("utils_extract_extracted_size_bytes",(-s $test_filename));
       while (my ($k, $v) = each %$run_stats) {