Chapter 3: Component Tuning

Concurrency

The Instances/Concurrency setting in the EAServer Manager Component Properties dialog box specifies whether component instances can execute concurrently on multiple threads. You can also set this property as com.sybase.jaguar.component.thread.safe using jagtool.

Enable this option for any component that is thread-safe. Concurrent access can decrease the response time of client method invocations. If this option is disabled, EAServer serializes all method calls to the component. Concurrency applies to execution of all instances. With concurrency disabled, a call to one instance cannot overlap the execution of another instance.

If the Sharing setting is enabled for your PowerBuilder component, disable the Concurrency setting. PowerBuilder is thread-safe at the session level only. For other component types, concurrency requires that your implementation be thread-safe. The requirements depend on the value of the Sharing setting as described in Table 3-1.

**Table 3-1: Coding requirements to support concurrency**
Sharing enabled?	Coding requirements
No	Protect any static instance variables; synchronize access to them to prevent concurrent access from different threads. Exceptions to this rule are read-only static variables, such as those that include the final modifier (meaning it is a constant that cannot be changed), and static variables defined as a primitive datatype that is 32 bits or less.
Yes	Same as the above, but you must protect all instance variables since one instance is called by multiple threads.

If you enable the Concurrency setting for a component that does not meet these requirements, you may encounter hard-to-diagnose threading errors such as race conditions. In a race condition, multiple threads update the same data simultaneously. The outcome of conflicting updates is unpredictable and may cause crashes or incorrect results.

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