Re: Relieving some ClassLoader contention in PreferredClassProvider

Peter Jones wrote:
> On Thu, Jan 04, 2007 at 04:56:41PM -0600, Gregg Wonderly wrote:
>> Peter Jones wrote:
>>
>>> Just to be clear, is the network activity that you are concerned about
>>> only the name->address resolution done by SocketPermission.implies
>>> during PreferredClassProvider.createClassLoader?  Or is it also the
>>> resolution potentially done by URL.equals during the table lookup and
>>> the "boomerang" search (PreferredClassProvider.findOriginLoader)?
>> I am interested in acceptable behavior in both cases.  The
>> .implies() is one thing that causes all URLs to be queried (one
>> optimization I added was to check for an HttpURLConnection instance
>> and request a "HEAD" instead of "GET").  A non operating codebase
>> host, will hang all threads for at least the TCP timeout period
>> foreach URL.openConnection() at least.  So, I am really concerned
>> overall about minimizing the impact any particular failure has on
>> unrelated threads.
>
> Wait, are you suggesting that an actual HTTP request is attempted
> during the process of getting the permission for each codebase URL?
> That is certainly not expected (or desired), so if it is indeed
> happening for you, then something is wrong and we need to figure out
> why (and I wonder if it is the high order cause of the problems that
> you have been seeing).  Despite its name, invoking URL.openConnection
> (or invoking getPermission on the returned URLConnection) is not
> supposed to actually make an HTTP connection (see the main class doc
> for URLConnection-- only connect() and other methods that require a
> connection to be made should do so).  So the procedure done by
> PreferredClassLoader.addPermissionsForURLs should not cause any HTTP
> connections to the codebase URLs-- only perhaps host name->address
> resolution because of what SocketPermission.implies does.
>

I certainly recall investigating a codebase issue where I wandered
through addPermissionsForURLs() and discovered the name resolution
hehaviour.  Can't recall it opening connections tho' (but my
recollection is vague).

Dan.

> -- Peter
>
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