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Oracle Workflow API Reference

Part Number B12163-02
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Synchronous, Asynchronous, and Forced Synchronous Processes

A workflow process can be either synchronous or asynchronous. A synchronous process is a process that can be executed without interruption from start to finish. The Workflow Engine executes a process synchronously when the process includes activities that can be completed immediately, such as function activities that are not deferred to the background engine. The Workflow Engine does not return control to the calling application that initiated the workflow until it completes the process. With a synchronous process, you can immediately check for process results that were written to item attributes or directly to the database. However, the user must wait for the process to complete.

An asynchronous process is a process that the Workflow Engine cannot complete immediately because it contains activities that interrupt the flow. Examples of activities that force an asynchronous process include deferred activities, notifications with responses, blocking activities, and wait activities. Rather than waiting indefinitely when it encounters one of these activities, the Workflow Engine sets the audit tables appropriately and returns control to the calling application. The workflow process is left in an unfinished state until it is started again. The process can be restarted by the Notification System, such as when a user responds to a notification; by the background engine, such as when a deferred activity is executed; or by the Business Event System, such as when an event message is dequeued from an inbound queue and sent to the workflow process. With an asynchronous process, the user does not have to wait for the process to complete to continue using the application. However, the results of the process are not available until the process is completed at a later time.

In addition to regular synchronous and asynchronous processes, the Workflow Engine also supports a special class of synchronous processes called forced synchronous processes. A forced synchronous process completes in a single SQL session from start to finish and never inserts into or updates any database tables. As a result, the execution speed of a forced synchronous process is significantly faster than a typical synchronous process. The process results are available immediately upon completion. However, no audit trail is recorded.

There may be cases when your application requires a forced synchronous process to generate a specific result quickly when recording an audit trail is not a concern. For example, in Oracle Applications, several products require Account Generator workflows to generate a meaningful flexfield code derived from a series of concatenated segments pulled from various tables. The Account Generator workflows are forced synchronous processes that compute and pass back completed flexfield codes to the calling applications instantaneously.

To create a forced synchronous process, you need to set the item key of your process to #SYNCH or to wf_engine.eng_synch, which returns the #SYNCH constant, when you call the necessary WF_ENGINE APIs. Since a forced synchronous process never writes to the database, using a non-unique item key such as #SYNCH is not an issue. Your process definition, however, must adhere to the following set of restrictions:

Attention: If you encounter an error from a forced synchronous process, you should rerun the process with a unique item key in asynchronous mode and check the error stack using the Workflow Monitor or the script wfstat.sql. If the synchronous process completes successfully, the error you encountered in the forced synchronous process is probably due to a violation of one of the above listed restrictions. See: Wfstat.sql, Oracle Workflow Administrator's Guide.

Note: The item key for a process instance can only contain single-byte characters. It cannot contain a multibyte value.

See Also

Synchronous, Asynchronous, and Forced Synchronous Workflows, Oracle Workflow Administrator's Guide

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