Program 13-1 main: The Main Service Entry Point in .NET framework

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Program 13-1 main: The Main Service Entry Point
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#include "EvryThngh" void WINAPI ServiceMain (DWORD argc, LPTSTR argv []); static LPTSTR ServiceName = _T ("SocketCommandLineService"); /* Main routine that starts the service control dispatcher */ VOID _tmain (int argc, LPTSTR argv []) { SERVICE_TABLE_ENTRY DispatchTable [] = { { ServiceName, ServiceMain }, { NULL, NULL } }; if (!StartServiceCtrlDispatcher (DispatchTable)) ReportError (_T ("Failed to start srvc ctrl dis"), 1, TRUE); /* ServiceMain () will not run until started by the SCM */ /* Return here only when all services have terminated */ return; }
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The ServiceMain() Functions
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These functions are specified in the dispatch table, as shown in Program 13-1, and represent logical services The functions are essentially enhanced versions of the base program that is being converted to a service, and each logical service will be invoked on its own thread by the SCM A logical service may, in turn, start up additional threads, such as the server worker threads that were used in serverSK and serverNP Frequently, there is just one logical service within a service In Program 13-2, the logical service is adapted from the main server shown in Program 12-2 It would be possible, however, to run both socket and named pipe logical services under the same Windows service, in which case two service main functions would be supplied While the ServiceMain() function is an adaptation of a main() function with argument count and argument string parameters, there is one small change The function should be declared void rather than having an int return value the way that a normal main() function would Extra code is required to register the service control handler, which is a function called by the SCM to control the services
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Registering the Service Control Handler
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A service control handler, called by the SCM, must be able to control the associated logical service The console control handler in serverSK, which sets a global shutdown flag, illustrates, in limited form, what is expected of a handler First, however, each logical service must immediately register a handler using the RegisterServiceCtrlHandlerEx function The function call should be at the beginning of ServiceMain() and not called again The SCM, after receiving a control request for the service, calls the handler SERVICE_STATUS_HANDLE RegisterServiceCtrlHandlerEx ( LPCTSTR lpServiceName, LPHANDLER_FUNCTION_EX lpHandlerProc, LPVOID lpContext)
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Parameters
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lpServiceName is the user-supplied service name provided in the service table entry for this logical service lpHandlerProc is the address of the extended handler function, which will be described in a later section The extended handler form was added to NT5, with RegisterServiceCtrlHandlerEx superseding RegisterServiceCtrlHandler The next parameter was also added to NT5 lpContext is user-defined data passed to the control handler This allows a single control handler to distinguish between multiple services using the same handler The return value, which is a SERVICE_STATUS_HANDLE object, is 0 if there is an error, and the usual methods can be used to analyze errors
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Setting the Service Status
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Now that the handler is registered, the next immediate task is to set the service status to SERVICE_START_PENDING using SetServiceStatus SetServiceStatus will also be used in several other places to set different values, informing the SCM of the service's current status A later section and Table 13-3 describe the valid status values in addition to SERVICE_START_PENDING
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Table 13-3 Controls That a Service Accepts (Partial List)
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Value Meaning
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SERVICE_ACCEPT_STOP SERVICE_ACCEPT_PAUSE_CONTINUE
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Enables the SERVICE_CONTROL_STOP Enables SERVICE_CONTROL_PAUSE and SERVICE_CONTROL_CONTINUE Notifies the service when system shutdown occurs This enables the system to send a SERVICE_CONTROL_SHUTDOWN value to the service Requires NT5 The startup parameters can change without restarting The notification is SERVICE_CONTROL_PARAMCHANGE
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SERVICE_ACCEPT_SHUTDOWN (The ControlService function cannot send this control code)
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SERVICE_ACCEPT_PARAMCHANGE
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The service control handler must set the status every time it is called, even if there is no status change Furthermore, any of the service's threads can call SetServiceStatus at any time to report progress, errors, or other information, and services frequently have a thread dedicated to periodic status updates The time period between status update calls is specified in a member field in a data structure parameter The SCM can assume an error has occurred if a status update does not occur within this time period BOOL SetServiceStatus ( SERVICE_STATUS_HANDLE hServiceStatus, LPSERVICE_STATUS lpServiceStatus)
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