Source

File: wp-admin/includes/class-wp-upgrader.php

public static function create_lock( $lock_name, $release_timeout = null ) {
		global $wpdb;
		if ( ! $release_timeout ) {
			$release_timeout = HOUR_IN_SECONDS;
		}
		$lock_option = $lock_name . '.lock';

		// Try to lock.
		$lock_result = $wpdb->query( $wpdb->prepare( "INSERT IGNORE INTO `$wpdb->options` ( `option_name`, `option_value`, `autoload` ) VALUES (%s, %s, 'no') /* LOCK */", $lock_option, time() ) );

		if ( ! $lock_result ) {
			$lock_result = get_option( $lock_option );

			// If a lock couldn't be created, and there isn't a lock, bail.
			if ( ! $lock_result ) {
				return false;
			}

			// Check to see if the lock is still valid. If it is, bail.
			if ( $lock_result > ( time() - $release_timeout ) ) {
				return false;
			}

			// There must exist an expired lock, clear it and re-gain it.
			WP_Upgrader::release_lock( $lock_name );

			return WP_Upgrader::create_lock( $lock_name, $release_timeout );
		}

		// Update the lock, as by this point we've definitely got a lock, just need to fire the actions.
		update_option( $lock_option, time() );

		return true;
	}