wsbpel message

Subject: Issue - 36 - Multiple instances of event handler

From: ws-bpel issues list editor<peter.furniss@choreology.com>
To: wsbpel@lists.oasis-open.org
Date: Wed, 9 Jul 2003 22:39:50 +0100

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Issue - 36 - Multiple instances of event handler

Status: open
Categories: enhancement/clarification
Date added: 9 Jul 2003
Submitter: Assaf Arkin
Date submitted: 09 July 2003
Document: Specification
Description: An onMessage event handler is written to receive some input message (as identified by the operation), assign it to some variable and then perform some work based on the content of that message.

An input message targeting that event handler is received by the process (M1). A new instance of the event handler is started, the message is assigned to the specified variable and work begins based on the value of that variable.

At which point another input message targeting the same event handler is recieved by that process (M2). A new instance of the event handler is started, the message is assigned to the specified variable and work begins based on the value of that variable.

Except that the first instance has not completed all work yet. While it started performing some work using the variable value from M1, it suprisingly finds that the new value of the variable is coming from M2.

Currently the spec does not indicate that these two instances will be serialized with respect to each other, nor that these two variables are distinct and not the same (variable instances are per process or some enclosing scope). Scoping does not alleviate the race condition since a new scope must be created and the values assigned to its variables, giving enough overlap between the two instances for a race condition to exist.

There seems to be no measure in the spec that allows for multiple instances of an event handler to occur concurrently, yet the spec suggests that this is possible.
Changes: 9 Jul 2003 - new issue

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