Marcus Crafter wrote:
Hi Berin,
On Tue, Dec 18, 2001 at 11:20:18AM -0500, Berin Loritsch wrote:
In what way are the same set of parameters used by different threads in
Cocoon?
We never addressed ThreadSafety as one of the Contracts for either
Parameters
or Configuration.
Have a look at this snippet from a generated sitemap:
----------------------
public class sitemap_xmap extends AbstractSitemap {
static final String LOCATION = "org.apache.cocoon.www.sitemap_xmap";
static {
dateCreated = 1007984808622L;
}
/** An empty <code>Parameter</code> used to pass to the sitemap components */
private Parameters emptyParam = new Parameters();
/** HashMap relating labels to view names */
private HashMap view_label_map = new HashMap(1);
<snip>...
if (isSelected("userstatus", "permitted", listOfMaps,
emptyParam, objectModel)) {
----------------------
The 'emptyParam' is passed into several cocoon components. If a
developer sets a parameter in a selector for example, then 2
threads can overwrite each other with different results (the current
problem we have here).
Is emptyParam supposed to be a read-only object, or something that is started
at the beginning of a pipeline?
In Cocoon I think the problem is more fundamental in that the
parameters object is actually an instance level reference in the
sitemap object (I'm not sure if that was intended ? ie. to share
parameters between pipelines), but I think even a thread safe
parameters object would not fix thread safety there - there
needs to be a local Parameters object per thread passing through
the sitemap, or a read-only Parameters object if the developer
shouldn't be doing this at all.
Yep, this can only be fixed with ThreadLocal parameters objects.
If the Parameters object remains thread unsafe, perhaps it should be
documented in it's class level javadocs like the Collection
classes so it's obvious to the developer (I'll submit a patch if
you like ?).
Sounds good.
--
"They that give up essential liberty to obtain a little temporary safety
deserve neither liberty nor safety."
- Benjamin Franklin
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