# Writing event hooks called from C extensions

**URL:** <https://www.ruby-forum.com/t/writing-event-hooks-called-from-c-extensions/138801>\
**Category:** Ruby\
**Created:** [May 27, 2008, 9:48pm UTC](https://www.ruby-forum.com/t/writing-event-hooks-called-from-c-extensions/138801 "2008-05-27T21:48:12Z")\
**Posts on this page:** 3\
**Page:** 1

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**Author:** ![mlangenberg](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/a87d85/32.png) [@mlangenberg](https://www.ruby-forum.com/u/mlangenberg)\
**Post date:** [May 27, 2008, 9:48pm UTC](https://www.ruby-forum.com/t/writing-event-hooks-called-from-c-extensions/138801/1 "2008-05-27T21:48:12Z")

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Just for educational purposes, I’m trying to write a Ruby-C extension  
that allows me to hook into Carbon’s event handler. So I can handle  
mouse clicks in Ruby.  
Mouse clicks (like all events) happen asynchronously, meaning that  
something needs to be running inside a seperate thread, but I find it  
hard to grasp how this all works out.

I’ve already figured out the following code: [http://pastie.org/204180](http://pastie.org/204180).  
This allows me to include the ‘MouseEvents’ module somewhere and call  
‘hook’. This works, and prints ‘click’ to my console, but it blocks  
ruby.

Would it be possible to start a seperate Thread from inside the C  
extension, which calls into ruby (or executes a block) asynchronously?

- Matt

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<div class="post-metadata">

**Author:** ![mlangenberg](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/a87d85/32.png) [@mlangenberg](https://www.ruby-forum.com/u/mlangenberg)\
**Post date:** [May 28, 2008, 3:32pm UTC](https://www.ruby-forum.com/t/writing-event-hooks-called-from-c-extensions/138801/2 "2008-05-28T15:32:31Z")

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On Tuesday 27 May 2008 21:44:37 Matthijs L. wrote:

> ruby.
> 
> Would it be possible to start a seperate Thread from inside the C  
> extension, which calls into ruby (or executes a block) asynchronously?

Not really, the problem is, ruby isn’t exactly multi-threading atm  
(somebody  
correct me if i’m wrong), 1.8 doesn’t use OS threads at all and  
concurrency  
is done by timeslicing, 1.9 does use native threads but only one thread,  
but  
VM is shared so only one thread can run at a time.

I don’t know Carbon but as i see it you have two options - first, if  
you’re  
happy with using just the hooker functions, you can simply call the ruby  
function from inside your myeventhandler(s), of course you can’t run any  
other code parallel to event handling (unless you start another ruby  
interpreter and synchronize somehow).

Second, you can abandon RunApplicationEventLoop and use manual event  
polling  
(i’m sure Carbon has one), then you can write the event handling as C  
function that takes block and iterates it - it would then be used from  
ruby  
as:

…  
register\_hooks()  
…  
loop\_events() do

# do some stuff

end # here the C function polls next event and if any, calls the  
appropriate  
ruby hooked functions,

Jan

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<div class="post-metadata">

**Author:** ![mlangenberg](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/a87d85/32.png) [@mlangenberg](https://www.ruby-forum.com/u/mlangenberg)\
**Post date:** [May 28, 2008, 4:50pm UTC](https://www.ruby-forum.com/t/writing-event-hooks-called-from-c-extensions/138801/3 "2008-05-28T16:50:33Z")

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On #ruby-lang, drbrain explained to me that I should run my event loop  
handler inside a seperate thread.  
I understand why that should be, but I’ve no clue how to launch a  
seperate thread from a C extension and communicatie back to the Ruby  
thread.  
Can anybody give me a head start?

- Matt

On Tue, May 27, 2008 at 9:44 PM, Matthijs L.