Topics:[[BR]]

* Common pitfalls.[[BR]]

* Current patterns.[[BR]]

Those are the areas where we have some threading:[[BR]]
* WebWorkers[[BR]]
* FileAPI[[BR]]
* Database (IconDatabase)[[BR]]
* Compositor (Chromium specific)[[BR]]
* Audio API[[BR]]

WebWorkers (david_levin):[[BR]]
* Mostly uses queue of tasks to pass messages between threads[[BR]]
* Also some template magic to do the boiler plate code for message handling[[BR]]

Compositor[[BR]]
* Another good pattern[[BR]]
* Very specific to this code[[BR]]
* Have to do a lot of explicit copies of some data structure (String...)[[BR]]
* Common data structure are not designed to be shared (mainly String agian)[[BR]]

Audio API[[BR]]
* They share the nodes between threads[[BR]]
* Had had to create a new sharing model[[BR]]
* The high priority audio thread is the one destroying the nodes[[BR]]
* Not sure it should be generalized as it uses background threads' priority to solve some of the lifetime issues[[BR]]

Current situation:[[BR]]
* Sharing is bad as most objects are not designed to be shared[[BR]]
* Strings for example are not shareable through threads (for performance)[[BR]]
* Locking also is difficult to get right[[BR]]
* Keep things isolated between threads![[BR]]
* Don't do sharing! Difficult bugs too![[BR]]
* Lots of copies involved to avoid sharing![[BR]]
* Currently to be called back on the main thread, we use a Timer that is expensive and we need to keep some state.[[BR]]
* Some dispatching API for running a task on this specific thread[[BR]]
* XHR, File, IconDB all go back to the main thread[[BR]]
* SQLDB has either to handle mainThread or another thread.[[BR]]
* Ping-ponging easy to get wrong, you would need some object to handle that![[BR]]
* Example is the DB where you don't need to send a CleanUp task when the thread is dead.[[BR]]

* Future patterns: http://trac.webkit.org/wiki/ThreadCommunication [[BR]]

Why not a templated cross-shared String?[[BR]]
* Problem with performance![[BR]]
* There is some mitigation already (semi efficient implementation for long String that avoid copying)[[BR]]

Why not develop a push API for GraphicsContext?[[BR]]

Issues[[BR]]
* WebWorker complex because the lifetimes of both thread are independent[[BR]]

Proposal (see link)[[BR]]
* Template magic to match the API (like this is a String or something else)[[BR]]
* Currently using raw pointers so we will need to Decorate them[[BR]]
* Lifetime to be determined by the 'originated' thread[[BR]]
* At some point, share code of Tasks, MessageQueues... in a common implementation somehow[[BR]]


* Moving to a dispatch type model (thread pool, etc.) -- proposal (ap?, jchaffraix?).[[BR]]

Somebody (sorry I did not take his name) called this: SystemWorldThread[[BR]]
* Some threading cannot be moved to that (Audio...)[[BR]]
* Some problem with some models[[BR]]
* Maybe need some models[[BR]]
* Game engines push the Audio to its own thread, the rest uses ThreadPools[[BR]]
* Maybe not a size-fits-all solutions[[BR]]
* Lots of values in having common Task[[BR]]
* jchaffraix needs to sync with Ap about an API for that.[[BR]]

Current work (https://bugs.webkit.org/show_bug.cgi?id=43903):[[BR]]
* Parallelize SVG filters[[BR]]
* Nice performance improvements[[BR]]
* Also implemented a first API inspired by OpenMP[[BR]]
* However there are others libraries / API available for multi-threading[[BR]]

* What to parallelize.[[BR]]

Not treated.