Hi Mike, FYI, I wrote a wip patch for Gecko. https://bugzilla.mozilla.org/show_bug.cgi?id=559092 Test builds will be here: https://build.mozilla.org/tryserver-builds/opet...@mozilla.com-xhr_priority/
-Olli On 4/13/10 8:36 PM, Mike Belshe wrote:
On Tue, Apr 13, 2010 at 9:36 AM, Olli Pettay <olli.pet...@helsinki.fi <mailto:olli.pet...@helsinki.fi>> wrote: Hi, Thanks for the comments. this seems like a pretty useful, yet reasonable easily implementable feature. Good to hear. I'd add 5th value "NORMAL", which would be the default value. const unsigned short CRITICAL = 0; const unsigned short HIGH = 1; const unsigned short NORMAL = 2 const unsigned short LOW = 3; const unsigned short LOWEST = 4; Not sure if we need all the values, or would HIGH, NORMAL, LOW be enough? I'm not fussy about what priorities are exposed or what we call them - so long as they are relatively few in number to avoid unnecessary complexity. (e.g. 3-5 priority buckets seems fine) Mike -Olli On 4/13/10 7:13 PM, Mike Belshe wrote: Hi, I'm a developer on the chrome team, and also working on SPDY. Others here at Google have requested that we expose some of the priority-based resource loading mechanics to applications so that applications can hint to the browser more information about which resources are critical and which are not. Some of the Google Apps teams have already implemented their own, manual priority-based resource fetchers, and our maps team saw a huge latency reduction as a result of doing so. Internally to chromium and webkit, resource loading is also priority-aware today. Finally, in SPDY, we've observed good improvements by exposing priorities all the way across the protocol. We believe exposing priority on the XHR object may benefit many applications manage their resource loads. Here is a quick writeup of one proposal which we think would work in browsers. We believe it is backward compatible with existing XHR, and can be optionally implemented. It also leaves a fair amount of the tuning at the discretion of the browser, so it does not create a long-term liability in the browser. We hope that these considerations make it an easy choice to approve. I'm wondering if the XMLHttpRequest group would be interested in taking this on? Thanks, Mike XMLHttpRequest Priority Fetching Every performant web browser implementation today implements various heuristics for resource loading prioritization internally. The notion is simple, that loading some resources, such as images, are less performance critical than loading other resources, such as external style sheets. By implementing basic priorities, browsers achieve substantially better performance loading web pages. Today, however, web applications have no way of giving hints to the browser about what may be high or low priority. Because complex applications heavily rely on resource loading by way of XmlHttpRequest, we propose a simple, backward compatible, and optional mechanism whereby application developers can hint to a browser how to load a XmlHttpRequest. Proposed API: interface XMLHttpRequest { // XMLHttpRequest Priorities. const unsigned short CRITICAL = 0; const unsigned short HIGH = 1; const unsigned short LOW = 2; const unsigned short LOWEST = 3; // Set the load priority for this request. void setPriority(unsigned short priority); } Example Usage: var client = new XMLHttprequest; client.setPriority(HIGH); client.open(’GET’, ‘demo.cgi’); client.send(); Description: When a new XMLHttpRequest object is created, it contains a notion of priority. Browsers which schedule resource fetches may optionally use this priority to determine in which order resources are fetched. 4 priorities are provided. By keeping the number of different priorities small, we keep browser and XMLHttpRequest priority implementations simple. By default, all XMLHttpRequest objects have a priority ‘LOW’. Applications may alter the priority by calling the setPriority() method on the XMLHttpRequest object. The priority set on the object at the time the applicaiton calls the XMLHttpRequest.send() method determines the priority the browser should use when fetching this resource. Calling setPriority() after the send() method will have no effect on the priority of the resource load. Browsers are not required to support the priority requested by applications, and may ignore it altogether. However, browsers are encouraged to support the requested priority order. The following is a description of one possible prioritization policy: CRITICAL resources are loaded first. When CRITICAL resources are in progress, requests for HIGH/MEDIUM/LOW resources are deferred until all CRITICAL resources have finished. HIGH/MEDIUM/LOW resources are loaded in that order. When no CRITICAL resources are in progress, HIGH/MEDIUM/LOW resources will be loaded with HIGH priority first. The browser does not need to wait until higher priority resources have finished fetching before it starts a request for a lower priority resource, although it may chose to do so. Existing Implementations: Google is currently using resource prioritization techniques in its Google Maps application, internally to the Google Chrome browser, and also as a part of the SPDY protocol.
