Easily measure PHP performance timing

stopwatch.php

<?php
/**
 * Little helper class to help you measure server performance
 *
 * Usage:
 * $stopwatch = new Stopwatch();
 * $stopwatch->start('My expensive operation');
 * // Do expensive operation
 * $stopwatch->stop();
 *
 * $stopwatch->start('My other expensive operation');
 * $stopwatch->stop('My other expensive operation');
 *
 * $stopwatch->read();
 *
 * Note: you can also pass this through to your Timber context
 * $context['stopwatch'] = $stopwatch;
 * & use it like {{ stopwatch.start('Render expensive part') }}
 */

class Stopwatch {
	public function __construct() {
		$this->entries = array();
	}

	public function start( $label ) {
		$key = sanitize_title( $label );

		$this->entries[ $key ] = array(
			'label' => $label,
			'start' => microtime( true ),
			'end'   => null,
		);
	}

	public function stop( $label ) {
		$key = sanitize_title( $label );

		if ( isset( $this->entries[ $key ] ) ) {
			$this->entries[ $key ]['end'] = microtime( true );
		}
	}

	public function read() {
		$header = array();

		foreach ( $this->entries as $key => $value ) {
			$start = $value['start'];

			if ( ! $start ) {
				continue;
			}

			$label    = $value['label'] ?? $key;
			$end      = $value['end'] ?? microtime( true );
			$duration = ( $end - $start ) * 1000;

			array_push( $header, sprintf( '%s=%f; "%s"', $key, $duration, $label ) );
		}

		header( 'Server-Timing: ' . join( $header, ',' ) );
	}
}