Date: 2004-11-15T15:58:48
Editor: KenTam <[EMAIL PROTECTED]>
Wiki: Apache Beehive Wiki
Page: Controls/ControlsThreadingModel
URL: http://wiki.apache.org/beehive/Controls/ControlsThreadingModel
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= Controls Threading Model =
== Overview ==
What threading issues exist when using and writing controls?
Controls default to a single-threaded model -- only one thread at a time will
be executing code in a given control instance. This simplifies client and
authoring logic, but may result in excessive contention and sub-optimal
performance. Sophisticated control developers may choose to implement logic to
handle multiple threads and concurrent execution.
== Control Client ==
Client access to control instances (ie C''''''ontrolBeans) is always
thread-safe. Generated code + infrastructure manage concurrency issues:
* Concurrent calls to operations may block (depending on control
implementation and container)
* Concurrent calls to get/set properties block as necessary to maintain
coherency
* Concurrent calls to other ControlBean generated methods and APIs are
thread-safe.
* Event handlers are client code! Infrastructure may result in multiple event
handlers being invoked concurrently, client's responsibility to ensure handlers
are thread-safe.
== Control Implementation ==
By default, control implementations delegate responsibility for thread-safety
to the infrastructure, which provides a single-threaded environment for
implementations. This is semantically equivalent to marking every operation
and event handler method with "synchronized".
Implementations may choose to explicitly manage thread-safety issues themselves
by annotating the implementation class with the [EMAIL PROTECTED] annotation:
{{{
package org.apache.beehive.controls.api.bean;
public @interface ThreadingModel
{
public enum Policy = { SINGLE_THREADED, MULTI_THREADED }
public Policy value() default SINGLE_THREADED;
}
}}}
If an implementation specifies [EMAIL
PROTECTED](ThreadingModel.Policy.MULTI_THREADED)}}}, the infrastructure will
permit multiple threads to execute concurrently on operations and event
handlers. The implementation is expected to use standard Java concurrency
mechanisms to guarantee data coherency.
== Open Issues ==
* Is it necessary to talk about threading issues around client initializers /
ControlBean instantiation? Seems straight-forward.
