User Timing

W3C

User Timing

W3C Working Draft 8 May 2012

This version:
http://www.w3.org/TR/2012/WD-user-timing-20120508/
Latest version:
http://www.w3.org/TR/user-timing/
Latest Editor's Draft:
https://dvcs.w3.org/hg/webperf/raw-file/tip/specs/UserTiming/Overview.html
Previous version:
http://www.w3.org/TR/2011/WD-user-timing-20110901/
Editors:
Jatinder Mann, Microsoft Corp.,
Zhiheng Wang, Google Inc.,
Anderson Quach, Microsoft Corp. (Until March 2011)

Copyright © 2012 W3C® (MIT, ERCIM, Keio), All Rights Reserved. W3C liability, trademark and document use rules apply.

Abstract

This specification defines an interface to help web developers measure the performance of their applications by giving them access to high precision timestamps.

Status of this document

This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at http://www.w3.org/TR/.

This is the second Last Call Working Draft of "User Timing". It takes into account the High Resolution Time specification, and removes string constants.

Please send comments to public-web-perf@w3.org (archived) with [UserTiming] at the start of the subject line by .

A diff document with the previous draft is available.

This document is produced by the Web Performance Working Group. The Web Performance Working Group is part of the Rich Web Clients Activity in the W3C Interaction Domain.

You can find the latest Editor's Draft of this document in the W3C's Mercurial repository, which is updated on a regular basis.

Publication as a Working Draft does not imply endorsement by the W3C Membership. This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.

This document was produced by a group operating under the 5 February 2004 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.

Table of Contents

  1. 1 Introduction
  2. 2 Conformance requirements
  3. 3 Terminology
  4. 4 User Timing
    1. 4.1 Introduction
    2. 4.2 Extensions to the Performance Interface
    3. 4.3 The PerformanceMark Interface
    4. 4.4 The PerformanceMeasure Interface
    5. 4.5 Vendor Prefixes
  5. 5 Monotonic Clock
  6. Acknowledgements
  7. References

1 Introduction

This section is non-normative.

Web developers need the ability to assess and understand the performance characteristics of their applications. While JavaScript provides a mechanism to measure application latency (retrieving the current timestamp from the Date.now() method), the precision of this timestamp varies between user agents.

This document defines the PerformanceMark and PerformanceMeasure interfaces, and extensions to the Performance interface, which expose a high precision timestamp to developers so they can better measure the performance of their applications.

The following script shows how a developer can use the interfaces defined in this document to obtain timing data related to developer scripts. 

    <!doctype html>
    <html>
      <head>
      </head>
      <body onload="init()">
        <script>
           function init() 
           {
                performance.mark("startTask1");
                doTask1(); // Some developer code
                performance.mark("endTask1");
                
                performance.mark("startTask2");
                doTask2(); // Some developer code
                performance.mark("endTask2");

                measurePerf();
           }

           function measurePerf() 
           {
               var perfEntries = performance.getEntries("marks");
               for (i = 0; i < perfEntries.length; i++)
               {
                     if (window.console) console.log("Name: "        + perfEntries[i].name      + 
                                                     " Entry Type: " + perfEntries[i].entryType +
                                                     " Start Time: " + perfEntries[i].startTime + 
                                                     " Duration: "   + perfEntries[i].duration  + "\n");
               }
           }
        </script>
      </body>
    </html>

2 Conformance requirements

All diagrams, examples, and notes in this specification are non-normative, as are all sections explicitly marked non-normative. Everything else in this specification is normative.

The key words "MUST", "MUST NOT", "REQUIRED", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in the normative parts of this document are to be interpreted as described in RFC2119. For readability, these words do not appear in all uppercase letters in this specification. [RFC2119]

Requirements phrased in the imperative as part of algorithms (such as "strip any leading space characters" or "return false and abort these steps") are to be interpreted with the meaning of the key word ("must", "should", "may", etc) used in introducing the algorithm.

Some conformance requirements are phrased as requirements on attributes, methods or objects. Such requirements are to be interpreted as requirements on user agents.

Conformance requirements phrased as algorithms or specific steps may be implemented in any manner, so long as the end result is equivalent. (In particular, the algorithms defined in this specification are intended to be easy to follow, and not intended to be performant.)

The IDL fragments in this specification must be interpreted as required for conforming IDL fragments, as described in the Web IDL specification. [Web IDL]

3 Terminology

The construction "a Foo object", where Foo is actually an interface, is sometimes used instead of the more accurate "an object implementing the interface Foo".

The term DOM is used to refer to the API set made available to scripts in Web applications, and does not necessarily imply the existence of an actual Document object or of any other Node objects as defined in the DOM Core specifications. [DOM Level 3 Core]

A DOM attribute is said to be getting when its value is being retrieved (such as by author script), and is said to be setting when a new value is assigned to it.

The term "JavaScript" is used to refer to ECMA262, rather than the official term ECMAScript, since the term JavaScript is more widely known. [ECMA262]

4 User Timing

4.1 Introduction

This section is non-normative

The PerformanceMark and PerformanceMeasure interfaces, and extensions to the Performance interface, give web developers access to a high precision, monotonically increasing timestamp so they can better measure the performance characteristics of their applications.

4.2 Extensions to the Performance Interface

  partial interface Performance {
    void mark(DOMString markName);
    Array getMarks(optional DOMString markName);
    void clearMarks(optional  DOMString markName);

    void measure(DOMString measureName, optional DOMString startMark, optional DOMString endMark);
    Array getMeasures(optional DOMString measureName);
    void clearMeasures(optional DOMString measureName);
  };

mark method

This method stores a timestamp with the associated name (a "mark").

Parameters

in name type of DOMString

The name associated with the timestamp.

Mark names may be re-used within the same document. Each call to the mark() method stores a new timestamp under the specified mark name.

The mark name cannot be the same name as any of the attributes in the PerformanceTiming interface [Navigation Timing].

Recommended Mark Names

Developers are encouraged to use the following Recommended Mark Names to mark common interactions. The user agent is responsible for storing a new timestamp under the specified mark name for Recommended Mark Names, just like any user specified mark name. The user agent does not validate that the usage of the Recommended Mark Name is appropriate or consistent with its description.

"mark_fully_loaded"

The time when the page is considered fully loaded as marked by the developer in their application.

"mark_fully_visible"

The time when the page is considered completely visible to an end-user as marked by the developer in their application.

"mark_above_the_fold"

The time when all of the content in the visible viewport has been presented to the end-user as marked by the developer in their application.

"mark_time_to_user_action"

The time of the first user interaction with the page during or after a navigation, such as scroll or click, as marked by the developer in their application.

No Return Value

Exceptions

Throws a SYNTAX_ERR exception if the markName argument is the same name as an attribute in the PerformanceTiming interface.

getMarks method

If the markName argument is not specified, this method must return all of the marks and their associated DOMHighResTimeStamp time values.

If the markName argument is specified, this method must return all of the DOMHighResTimeStamp time values for the specified mark name.

If the markName argument is specified but it does not exist, this method must return an empty array.

Parameters

in markName type of DOMString

[optional] The name of the mark. If not specified, all marks are returned.

Return Value

Array

If the markName argument is not specified, the method returns an associative Array. Each key in the Array is a mark name. The value associated with the mark name is an Array of DOMHighResTimeStamp time values for that mark. In JSON notation, the data structure will look similar to this: { "mark1": [0.750, 1.125, 3.333], "mark2": [2.125] }.

If the markName argument is specified, and the mark name exists, the method returns an Array of DOMHighResTimeStamp time values. In JSON notation, the data structure will look similar to this: [0.500, 1.125, 3.750].

If the markName argument is specified, and the mark name does not exist, the method returns an empty Array. In JSON notation, the data structure will look similar to this: [].

Timestamps will be listed in the order that the mark() method was called.

The returned Array is a copy of data at the time that the getMarks() method was called.

No Exceptions

clearMarks method

If the markName argument is not specified, this method removes all marks and their associated DOMHighResTimeStamp time values.

If the markName argument is specified, this method removes all DOMHighResTimeStamp time values for the given mark name.

If the markName argument is specified but the specified markName does not exist, this method will do nothing.

Parameters

in markName type of DOMString

[optional] The name of the mark whose DOMHighResTimeStamp time values should be cleared. If not specified, all marks will be cleared.

No Return Value

No Exceptions

measure method

This method stores the DOMHighResTimeStamp duration between two marks along with the associated name (a "measure").

The behavior of this method depends on which arguments are specified:

The startMark and endMark arguments may be the name of one of the attributes in the PerformanceTiming interface [Navigation Timing]. In this case, the value of that attribute is used as the DOMHighResTimeStamp time value.

Parameters

in name type of DOMString

The name associated with the measure.

Measure names may be re-used within the same document. Each call to the measure() method stores a new duration under the specified measure name.

Measure names live independently from mark names.

in startMark type of DOMString

[optional] The name of the start mark.

If specified, the most recent DOMHighResTimeStamp time value of the start mark is used.

If not specified, navigationStart is used.

May be the name of one of the attributes in the PerformanceTiming interface [Navigation Timing]. In this case, the value of that attribute is used as the start DOMHighResTimeStamp time value.

in endMark type of DOMString

[optional] The name of the end mark.

If specified, the most recent DOMHighResTimeStamp time value of the end mark is used.

If not specified, the current time as a DOMHighResTimeStamp is used.

May be the name of one of the attributes in the PerformanceTiming interface [Navigation Timing]. In this case, the value of that attribute is used as the end DOMHighResTimeStamp time value.

No Return Value

Exceptions

Throws a SYNTAX_ERR exception if the start mark or end mark does not exist.

Throws an INVALID_ACCESS_ERR exception if either startMark or endMark argument, or both, have the same name as a PerformanceTiming attribute with a time value of 0.

getMeasures method

If the measureName argument is specified, this method must return all of the durations for the specified measure name.

If the measureName argument is not specified, this method must return all of the measures and their associated DOMHighResTimeStamp durations.

If the measureName argument is specified but it does not exist, this method must return an empty array.

Parameters

in measureName type of DOMString

[optional] The name of the measure to return. If not specified, all measures are returned.

Return Value

Array

If the measureName argument is not specified, the method returns an associative Array. Each key in the Array is a measure name. The value associated with the measure name is an Array of DOMHighResTimeStamp durations for that measure. In JSON notation, the data structure will look similar to this: { "measure1": [0.525, 5.125, 1.125], "measure2": [3.251] }.

If the measureName argument is specified, and the measure name exists, the method returns an Array of DOMHighResTimeStamp durations. In JSON notation, the data structure will look similar to this: [0.250, 5.125, 1.750].

If the measureName argument is specified, and the measure name does not exist, the method returns an empty Array. In JSON notation, the data structure will look similar to this: [].

Durations will be listed in the order that the measure() method was called.

The returned Array is a copy of data at the time that the getMeasures() method was called.

No Exceptions

clearMeasures method

If the measureName argument is not specified, this method removes all measures and their associated DOMHighResTimeStamp durations.

If the measureName argument is specified, this method removes all DOMHighResTimeStamp durations for the given measure name.

If the measureName argument is specified but the specified measureName does not exist, this method will do nothing.

Parameters

in measureName type of DOMString

[optional] The name of the measure whose DOMHighResTimeStamp durations should be cleared. If not specified, all measures will be cleared.

No Return Value

No Exceptions

4.3 The PerformanceMark Interface

  interface PerformanceMark : PerformanceEntry {
  };

The PerformanceMark interface also exposes marks created via the mark() method to the Performance Timeline. The PerformanceMark interface extends the following attributes of the PerformanceEntry interface:

The name attribute will return the mark's name.

The entryType attribute will return the DOMString mark.

The startTime attribute will return a DOMHighResTimeStamp with the the mark's time value.

The duration attribute will return a DOMHighResTimeStamp of value 0.

4.4 The PerformanceMeasure Interface

  interface PerformanceMeasure : PerformanceEntry {
  };

The PerformanceMeasure interface also exposes measures created via the measure() method to the Performance Timeline. The PerformanceMeasure interface extends the following attributes of the PerformanceEntry interface:

The name attribute will return the measure's name.

The entryType attribute will return the DOMString measure.

The startTime attribute will return a DOMHighResTimeStamp with the measure's start mark.

The duration attribute will return a DOMHighResTimeStamp with the duration of the measure.

4.5 Vendor Prefixes

Vendor-specific proprietary user agent extensions are discouraged. If such extensions are needed, e.g. for experimental purposes, vendors must use the following extension mechanisms:

If the extension to be added is a Standard Mark Name, the Standard Mark Name must:

5 Monotonic Clock

The time values stored within the interface must monotonically increase to ensure they are not affected by adjustments to the system clock. The difference between any two chronologically recorded time values must never be negative. The user agent must record the system clock at the beginning of the navigation and define subsequent time values in terms of a monotonic clock measuring time elapsed from the beginning of the navigation.

Acknowledgements

Thanks to Karen Anderson, Tony Gentilcore, Nic Jansma, James Simonsen, Steve Souders, Sigbjorn Vik, and Jason Weber for their useful comments that led to changes to this specification and their contributions to this work.

References

[IETF RFC 2119]
Key words for use in RFCs to Indicate Requirement Levels, Scott Bradner, Author. Internet Engineering Task Force, March 1997. Available at http://www.ietf.org/rfc/rfc2119.txt.
[IETF RFC 6454]
The Web Origin Concept, Adam Barth, Author. Internet Engineering Task Force, December 2011. Available at http://www.ietf.org/rfc/rfc6454.txt.
[DOM Level 3 Core]
Document Object Model Level 3 Core Specification, A. Le Hors, et al., Editors. World Wide Web Consortium, 7 April 2004. This version of the Document Object Model Level 3 Core Recommendation is http://www.w3.org/TR/2004/REC-DOM-Level-3-Core-20040407. The latest version of DOM4 is available at http://www.w3.org/TR/dom/.
[ECMA-262]
ECMAScript Language Specification, 5.1 Edition. ECMA International, Standard ECMA-262, June 2011. This version of the ECMAScript Language is available from http://www.ecma-international.org/publications/standards/Ecma-262.htm.
[Navigation Timing]
Navigation Timing, Zhiheng Wang, Editor. World Wide Web Consortium, March 2012. This version of the Navigation Timing specification is available from http://www.w3.org/TR/2012/CR-navigation-timing-20120313/. The latest version of Navigation Timing is available at http://www.w3.org/TR/navigation-timing/.
[Performance Timeline]
Performance Timeline, Jatinder Mann, et al, Editors. World Wide Web Consortium, May 2012. This version of the Performance Timeline specification is available from http://www.w3.org/TR/2012/WD-performance-timeline-20120508/. The latest version of Performance Timeline is available at http://www.w3.org/TR/performance-timeline/.
[High Resolution Time]
High Resolution Time, Jatinder Mann, Editor. World Wide Web Consortium, March 2012. This version of the High Resolution Time specification is available from http://www.w3.org/TR/2012/WD-hr-time-20120313/. The latest version of High Resolution Time is available at http://www.w3.org/TR/hr-time/.
[Web IDL]
Web IDL, Cameron McCormack, Editor. World Wide Web Consortium, April 2012. This version of the Web IDL specification is available from http://www.w3.org/TR/2012/CR-WebIDL-20120419/. The latest version of Web IDL is available at http://www.w3.org/TR/WebIDL/.