The ENUM_SERVICE_STATUS structure's members identify the service's name, the name Services Monitor will display for the service, and a nested structure called SERVICE_STATUS that contains information about the service's current status.
The fifth EnumServicesStatus parameter defines the size in bytes of the
fourth parameter's buffer. The sixth parameter returns the number of bytes the buffer needs to hold the array of ENUM_SERVICE_STATUS structures. Services Monitor allocates a buffer size of 16KB, which is larger than necessary in most cases. The seventh parameter contains the number of services the EnumServicesStatus function returns. The eighth parameter tells Services Monitor how far down the target SCM database's list of services to start enumerating services. This value needs to be 0.
When the EnumServicesStatus function call completes, it returns a new value
in the eighth parameter. If the function places a 0 in the eighth parameter, the
buffer is large enough to enumerate all the target machine's services. If the
function returns a non-zero value in the eighth parameter, the call failed, and
you need to check the value of the VB Err object's LastDLLError property. If
your computer's last DLL error is ERROR_MORE_DATA, the EnumServicesStatus buffer
is too small, and the eighth parameter's value identifies the entry in the SCM
database's services list where Services Monitor needs to resume enumeration when
the buffer has space for the remaining data. When Services Monitor encounters
the ERROR_MORE_DATA error, it increases the size of the buffer and tries
the EnumServicesStatus call again. Services Monitor continues to try the
EnumServicesStatus function call until the buffer is large enough and the call
completes successfully or the call returns an error other than ERROR_MORE_DATA.
Any other LastDLLError entry indicates that a more serious error prevents
Services Monitor from enumerating services; if it encounters an error other than
ERROR_MORE_DATA, Services Monitor exits.
At C, Listing 2 processes the array of ENUM_SERVICE_STATUS structures that
the EnumServicesStatus function returns and creates a CService object for each
service the EnumServicesStatus function adds to the colServices
collection. As Services Monitor processes the arrays, it uses the Tree View
control to display each server's list of services and each service's status. At
D, Listing 2 uses the CloseServiceHandle function to close the handle to the SCM
database.
Updating Services' Status
When the Services Monitor's polling timer expires, the application queries
the status of each selected service using the QueryServiceStatus API. Listing 3, page 193, shows the code that queries services' status.
At A, Listing 3 uses the OpenSCManager function to connect to the SCM
database. The value SC_MANAGER_CONNECT in OpenSCManager's third parameter
tells the function to open a connection.
At B, the OpenService function uses the handle that the OpenSCManager
function returns to acquire a handle to a service. The OpenService function
takes three parameters. The first parameter is the handle to the SCM database
that the OpenSCManager function returns. The second parameter is the service's
short name. The third parameter is a constant that specifies the permission
level the SCM operation needs. The value SERVICE_QUERY_STATUS gives the
OpenService function permission to return the service's status.
At C, Listing 3 uses the QueryServiceStatus function to retrieve the
service's current status. The QueryServiceStatus function takes two parameters.
The first parameter is the service handle that the OpenService function returns,
and the second parameter is a structure that contains the service's current
status. At D, Listing 3 uses the CloseServiceHandle function to close the
handles to the SCM database and the service.
Services Monitor's Functionality
This article uses the WNet and SCM APIs to build a Services Monitor
application. You can immediately put this utility to work on your network or
customize the code to fit your needs. Services Monitor provides a display and
alarm when a service fails, but you can modify the code to perform other
actions, such as send email or attempt to restart the failed service.
NT 5.0 will include another method for querying the status of services on
networked systems: Active Directory Services. Nevertheless, Services Monitor
offers service monitoring functionality, and the WNet and SCM APIs will continue
to support NT users for the foreseeable future.
End of Article
Prev. page
1
2
[3]
next page -->
