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Re: Thread safety in WO (was Re: Picking up .wo changes)
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Re: Thread safety in WO (was Re: Picking up .wo changes)


  • Subject: Re: Thread safety in WO (was Re: Picking up .wo changes)
  • From: Hsu <email@hidden>
  • Date: Mon, 9 Jun 2003 21:40:26 -0700

The WebObjects WODefaultAdaptor is always multi-threaded, but the request-handling is not (by default).

This means that WORequests will be read in parallel, processed according to WOAllowsConcurrentRequestHandling (default to false), and returned in parallel.

Karl

On Monday, June 9, 2003, at 09:42  AM, Jonathan Rochkind wrote:

At 08:07 AM 6/6/2003 -0700, Pierre Frisch wrote:
Concurrent request handling is the default behavior in WO 5.x and I would not bank to much on the ability to disable it. I remember reading somewhere that WO 5.x is always multithreaded and that you should never make the single thread assumption.

Hm. It's true that WO 5.x is always multithreaded, in that more than multiple threads will always exist at once. I do NOT think it's true that WO 5.x handles requests concurrently by default. The documentation for WOApplication.allowsConcurrentRequestHandling says "returns false by default."


The trick then, when you know that requests will not be handled concurrently but that the app is multithreaded, is figuring out in what circumstances more than one thread may be accessing any given piece of code. And I'm not always sure. Various knowledgeable developers who I respect have disagreed on this sort of thing on the list in the past.

For a piece of code that actually spans sessions, like an application-wide cache of WOElement definitions, I would agree that to be on the safe side you better write it in a thread-safe way, assuming the worst case in terms of multiple threads wanting to access it at once.

--Jonathan


Something like this should do, should it not: (well, I have to load the strings from somewhere too)

WOElement cachedTemplate;

public WOElement template()
{
if (cachedTemplate == null)
{
synchronized(cachedTemplate)
{
if (cachedTemplate == null)
cachedTemplate = templateWithHTMLString(htmlString, wodString, languages);
}
}
return cachedTemplate;
}
This would address one level of cache. You probably would like to cache the hit to the backing store when instantiating new components. You want to implement that with Dictionaries based on component name and language. I usually do a double level dictionary the first level is based on the component name and the second on the language. When a search is unsuccessful you probably want to tag it so as not to redo it.


Or perhaps I'll just forget about it all, and go back to PHP and MySQL again...
At least there I can look at the source code, if I wonder about something.
If you don't care about performance, you don't need caching and all is simple....


--anders
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--

Easy there, I know over two hundred ways to kill a man.
You could glue an open jar of rats to his face, then blowtorch the other side so the rats have to eat their way through his face.
... Two hundred one, then.


Homepage:
     http://homepage.mac.com/khsu/index.html
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