Serializable Scopes
Introduction
This sample focuses on the isolated
attribute of the scope activity along with its use and syntax. It
includes an example BPEL process that uses serializable scopes. For a
discussion of all other aspects of the scope activity, see The Scope Activity.
Serializable scopes provide concurrency control in governing access to a common set of shared variables. If two or more scopes are serializable, then access to any variable shared between them is controlled. Such scopes behave as if the scopes were executed in sequence (one after another), rather than concurrently.
The sample process, illustrated below, contains a sequence that starts with a receive activity that accepts a message containing an order. The sequence ends with a reply that returns a message containing a status string.
In between the receive and the reply is an assign that sets a status string to "Start", then a scope that sets the status first to "Ordering" and then to "Done ordering". Before doing so, the scope checks to make sure the status is not "Cancelled".
The process has an event handler that contains an onMessage that waits for a cancellation message. The onMessage contains a scope that handles incoming cancellation requests by setting the status variable's value to "Cancelled". Before doing so, it checks to make sure that the order scope has not yet started (the status is still "Start").
Both scopes have their isolated
attributes
set to "yes". Doing so makes sure that access to the status is
serialized;
that is, the two scopes can't execute at the same time.
The basic features and XML syntax of the scope activity are
described in
the Scope Sample documentation. Scopes that
have
their isolated attribute set to "yes"
are said
to be serializable. Such scopes provide concurrency control in
governing
access to shared variables. The engine guarantees that all access to
variables
shared between serializable scopes (and external to them) is
coordinated such
that conceptually all activities within each scope are completed before
or
after other serialized scopes—not concurrently.
Deploying the Process
Running
See Running the Samples.
The
service name to use is serializableScopeProcessService. The sample data
file
orderMessage.xml can be used as input for this example.
The reply
will contain the string "Done ordering".
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