No limitation exists for spawning multiple threads in a service application when concurrent tasks are to be fulfilled.
Class ServiceApp() Foundation
Class function of the ServiceApp class
Description
The ServiceApp class is used to implement service applications. Just like XppApplication() for console applications and XbpApplication() for GUI and hybrid mode applications, the ServiceApp class provides functionality for a specific application type. Please refer to the section Implementing services for technical background information on service applications.
The ServiceApp class is a singleton, which means that only the class object can be used and no instances can be created of the class. This reflects the fact that only one service can be implemented in a single executable file, and that only one application object is required per service application. Consequently, the ServiceApp class does not have a constructor method.
The ServiceApp class uses callbacks to implement the reaction of the service to particular service control requests like "start" or "stop". A minimum of two callbacks must be implemented: one callback containing the code for the task of the service, and another callback that allows to stop the service after it has been started. These callbacks are named :main() and :stop().
Class methods
:start()
Starts the service process.
Callback class methods
These class methods are called automatically by the system in response to control requests from a service control application. The callbacks must be used to implement the behavior of the service with regard to the control requests.
:continue()
Service received "continue" control request.
:main()
Service has started.
:pause()
Service received "pause" control request.
:stop()
Service received "stop" control request.
Examples
// This sample demonstrates how a service can be implemented.
// The service simply calls the function Tone() every
// five seconds until it receives the Stop request.
// To install and start this service see the
// example for the ServiceController class.
#include "service.ch"
// Entry point of the executable
PROCEDURE Main()
MyService():start()
RETURN
CLASS MyService From ServiceApp
EXPORTED:
CLASS METHOD main
CLASS METHOD stop
HIDDEN:
CLASS VAR lRunning
ENDCLASS
// Entry point of the service
CLASS METHOD MyService:main()
::lRunning := .T.
DO WHILE ::lRunning
Tone( 400, 9 )
Sleep( 500 )
ENDDO
RETURN self
// Entry point for Stop request
CLASS METHOD MyService:stop()
::lRunning := .F.
RETURN self
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