Re: Relieving some ClassLoader contention in PreferredClassProvider

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.

-- Peter

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