RE: [XHR] Event processing during synchronous request
Anne van Kesteren wrote: On Mon, Sep 10, 2012 at 10:05 AM, Mike Wilson mike...@hotmail.com wrote: Thanks. So I understand it is the HTML specification reference that provides details on this behaviour for the XHR spec. I'll look further there as its fetching section by itself doesn't directly express the relationship between synchronous and a stopped event loop (although as a programmer I can infer this relationship). Well yeah, shit's complicated. HTML fetch can be invoked either synchronously or asynchronously. When invoked synchronously it's as part of some task already and since the event loop is not manually spun no other tasks will run at that time. When invoked asynchronously HTML fetch itself queues tasks on the event loop that then cause various things to happen per XMLHttpRequest, such as dispatching progress events. Thanks, and yes, for me this section: http://www.whatwg.org/specs/web-apps/current-work/multipage/webappapis.html# event-loops has the sufficient text to define this. On the other hand, in: https://bugzilla.mozilla.org/show_bug.cgi?id=785243 Firefox implementors say that: sync XHR spins the event loop, so events (including async script execution and whatnot) can fire under a sync XHR call. which seems to suggest that the XHR spec should allow implementations to pump events during a synchronous fetch. What is the XHR spec teams's opinion on this? Best regards Mike
Re: [XHR] Event processing during synchronous request
On Wed, Sep 12, 2012 at 8:35 PM, Mike Wilson mike...@hotmail.com wrote: On the other hand, in: https://bugzilla.mozilla.org/show_bug.cgi?id=785243 Firefox implementors say that: sync XHR spins the event loop, so events (including async script execution and whatnot) can fire under a sync XHR call. which seems to suggest that the XHR spec should allow implementations to pump events during a synchronous fetch. No, bz is just explaining the Gecko implementation. What is the XHR spec teams's opinion on this? That Gecko has a bug. -- http://annevankesteren.nl/
Re: [XHR] Event processing during synchronous request
On 9/12/12 7:35 PM, Mike Wilson wrote: On the other hand, in: https://bugzilla.mozilla.org/show_bug.cgi?id=785243 Firefox implementors say that: sync XHR spins the event loop, so events (including async script execution and whatnot) can fire under a sync XHR call. That's a comment about implementation of sync XHR in Gecko, not about the spec. -Boris
Re: [XHR] Event processing during synchronous request
On Sun, Sep 9, 2012 at 6:33 PM, Mike Wilson mike...@hotmail.com wrote: I didn't find statements directly addressing this in http://www.w3.org/TR/XMLHttpRequest/ or http://www.whatwg.org/specs/web-apps/current-work/multipage/fetching-resourc es.html but maybe there are indirect relationships between specification sections that I am missing? What you are missing is that for synchronous fetching the event loop stops working so incoming events will not be processed. -- http://annevankesteren.nl/
RE: [XHR] Event processing during synchronous request
Anne van Kesteren wrote: On Sun, Sep 9, 2012 at 6:33 PM, Mike Wilson mike...@hotmail.com wrote: I didn't find statements directly addressing this in http://www.w3.org/TR/XMLHttpRequest/ or http://www.whatwg.org/specs/web-apps/current-work/multipage/fe tching-resourc es.html but maybe there are indirect relationships between specification sections that I am missing? What you are missing is that for synchronous fetching the event loop stops working so incoming events will not be processed. Thanks. So I understand it is the HTML specification reference that provides details on this behaviour for the XHR spec. I'll look further there as its fetching section by itself doesn't directly express the relationship between synchronous and a stopped event loop (although as a programmer I can infer this relationship). Best regards Mike
Re: [XHR] Event processing during synchronous request
On Mon, Sep 10, 2012 at 10:05 AM, Mike Wilson mike...@hotmail.com wrote: Thanks. So I understand it is the HTML specification reference that provides details on this behaviour for the XHR spec. I'll look further there as its fetching section by itself doesn't directly express the relationship between synchronous and a stopped event loop (although as a programmer I can infer this relationship). Well yeah, shit's complicated. HTML fetch can be invoked either synchronously or asynchronously. When invoked synchronously it's as part of some task already and since the event loop is not manually spun no other tasks will run at that time. When invoked asynchronously HTML fetch itself queues tasks on the event loop that then cause various things to happen per XMLHttpRequest, such as dispatching progress events. -- http://annevankesteren.nl/
Re: [XHR] Event processing during synchronous request
On 09/09/2012 06:33 PM, Mike Wilson wrote: Is it defined how the browser should behave wrt calling unrelated event handlers in user code during synchronous XHR requests? (with unrelated I refer to events that are not related to the ongoing synchronous request itself) I didn't find statements directly addressing this in http://www.w3.org/TR/XMLHttpRequest/ or http://www.whatwg.org/specs/web-apps/current-work/multipage/fetching-resourc es.html but maybe there are indirect relationships between specification sections that I am missing? Or maybe it's deliberately undefined? I ask because Firefox behaves differently to the other popular browsers, in that it triggers event handlers for other asynchronous XHR requests while blocking for a synchronous XHR request. That is a well-known bug in Gecko (other engines have or have had different kinds of bug related to sync XHR, like locks etc). But since synchronous XHR in UI-thread is by all means effectively deprecated and very bad for the ux, I wouldn't expect the bug in Gecko to be fixed any time soon (at least not by me :) ). -Olli Thanks Mike Wilson
