File: handle stats for recursive transformation calls

TimingMetric->start() and stop() cannot handle recursion due to statefulness.

To fix, we'll measure the metric manually so that the sample will be
captured in a single operation.

Bug: T367110
Bug: T367928
Change-Id: I663d32e0211df35d5295bf2a09175e6fdcb4c5ed

includes/filerepo/file/File.php

@@ -1320,15 +1320,20 @@ public function generateAndSaveThumb( $tmpFile, $transformParams, $flags ) {
  $this->generateBucketsIfNeeded( $normalisedParams, $flags );
  }
 
- $timer = $statsFactory->getTiming( 'media_thumbnail_generate_transform_seconds' )
- ->copyToStatsdAt( 'media.thumbnail.generate.transform' );
- $timer->start();
+ # T367110
+ # Calls to doTransform() can recur back on $this->transform()
+ # depending on implementation. One such example is PagedTiffHandler.
+ # TimingMetric->start() and stop() cannot be used in this situation
+ # so we will track the time manually.
+ $starttime = microtime( true );
 
  // Actually render the thumbnail...
  $thumb = $handler->doTransform( $this, $tmpThumbPath, $thumbUrl, $transformParams );
  $tmpFile->bind( $thumb ); // keep alive with $thumb
 
- $timer->stop();
+ $statsFactory->getTiming( 'media_thumbnail_generate_transform_seconds' )
+ ->copyToStatsdAt( 'media.thumbnail.generate.transform' )
+ ->observe( ( microtime( true ) - $starttime ) * 1000 );
 
  if ( !$thumb ) { // bad params?
  $thumb = false;