Threading issues and component types
Each instance of a PowerBuilder component executes in its
own session, and each session can support only one thread of execution.
Therefore a single PowerBuilder component instance cannot simultaneously
execute multiple client requests. However, multiple instances of
the same component can each execute a separate client request. When
you create a component, PowerBuilder sets default values for several
properties that affect the way threads are handled in EAServer.
Using the Thread Manager
You can also use the EAServer Thread
Manager to develop more robust services. See “Using the EAServer Thread Manager”.
Concurrency property
The Concurrency property determines
whether multiple instances of a component can be created to handle
multiple client requests. Checking the Concurrency check box in
the wizard or the Project painter sets the com.sybase.jaguar.component.thread.safe
property to TRUE.
Standard components
For standard components, you can improve performance by allowing
multiple instances of a component to handle client requests. The
default setting for the concurrency property for standard components
is checked, but you can change the setting if you want only one instance
of a given component.
Shared components
For shared components, only one instance of the component
should be active at any time and therefore only one thread can be executed.
The Concurrency check box is disabled and not checked for shared components.
Service components
Although service components are usually treated as shared
components, you can choose to create more than one instance of a service
component to improve performance and scalability. There are three options
on the Components page that interact for service components: Concurrency,
Automatic Demarcation/Deactivation, and Create Instances
(the Create Instances option can be changed only for service components).
When you change the Create Instances option to 2 or more,
the Concurrency check box and the Automatic Demarcation/Deactivation
check box become checked. Multiple instances of the service component
can be created if necessary, and are deactivated after each method
call. If you clear the Automatic Demarcation/Deactivation
check box, so that you need to explicitly deactivate component instances,
the Create Instances check box is reset to 1 and the Concurrency
check box is cleared.
bind.thread, sharing, and tx_vote properties
There are three other component properties that affect the
handling of threads in EAServer:
sharing, tx_vote, and bind.thread.
Bind Object property not used
An additional
property, bind.object, enables client threads to execute in a single instance
but also supports creation of multiple instances. This property cannot be
used for PowerBuilder components and is always set to FALSE.
When the bind.thread property is set
to TRUE, a method on a component instance must
execute on the same thread that created the instance. This property
must be set to TRUE if you are using live editing
to build your component. It should be set to FALSE for
components that are deployed to UNIX servers to improve scalability.
The sharing property identifies whether
or not the component is shared. It is set to FALSE when
you select Standard in the wizard and to TRUE when
you select Shared or Service. The only way this property can be
changed in PowerBuilder is by changing the Create Instances setting
on the Components tab page for service components in the Project
painter. If either the sharing or thread.safe property is set to TRUE,
the other must be set to FALSE.
A component that can remain active between consecutive method
invocations is called a stateful component. A component that is
deactivated after each method call and that supports instance pooling
is said to be a stateless component. Typically, an application built
with stateless components offers the greatest scalability. The tx_vote
property determines whether the component is deactivated after every
method call. It is set to FALSE (stateless) if
you check the Automatic demarcation/deactivation check
box in the wizard or select more than one instance on the Component
page in the Project painter; otherwise it is set to TRUE (stateful).
You can have only one instance of a stateful service object.
Table 23-1 summarizes
the default setting for each type of component and shows which can
be changed.
|
Component |
bind.thread |
sharing |
thread.safe |
tx_vote |
|---|---|---|---|---|
|
Standard |
FALSE, mutable |
FALSE, immutable |
TRUE, mutable |
FALSE, mutable |
|
Shared |
FALSE, mutable |
TRUE, immutable |
FALSE, immutable |
FALSE, mutable |
|
Service (single instance) |
FALSE, mutable |
TRUE, immutable |
FALSE, mutable |
FALSE, mutable |
|
Service (multiple instances) |
FALSE, mutable |
FALSE, immutable |
TRUE, mutable |
FALSE, mutable If changed to TRUE, number of instances |
If you deploy a service component for which bind.thread, thread.safe,
and sharing are set to TRUE, EAServer disables the thread.safe
property automatically at runtime.