ASYNC_COMPLETION callback function (tspi.h)

Completion_Proc is a callback function implemented by TAPI and supplied to the service provider as a parameter to TSPI_providerInit. The service provider calls this function to report the completion of a line or phone procedure that it executes asynchronously.

The ASYNC_COMPLETION type defines a pointer to this callback function. Completion_Proc is a placeholder for the application-defined function name.



void AsyncCompletion(
  LONG lResult



The identifier passed in the original request that the service provider executed asynchronously.


The outcome of the operation. This can be zero to indicate success or a negative number to indicate an error. The possible specific error values that can result from a function are the same for asynchronous or synchronous execution.

Return value



The call state when calling this function can be any state.

This procedure is supplied by TAPI at the time a service provider is initialized with the TSPI_providerInit function. Some of the TSPI procedures that operate on line, call, and phone devices specify asynchronous operation. These procedures include a dwRequestID parameter to identify the request. When such a procedure is called, the service provider can return a negative number for an error if one is detected immediately, or the positive dwRequestID if the operation continues asynchronously. The service provider must report completion exactly once for each request it executes asynchronously. It does so by calling this procedure. The service provider is not permitted to call this procedure or the Line_Event or Phone_Event procedure again until this procedure returns.

The service provider is permitted to call the Completion_Proc function before it returns from the first request. TAPI guarantees not to call the service provider from within the Completion_Proc context except where noted.

This does not have any direct correspondence at the TAPI level because at that level asynchronous function completions are reported as a message passed through the same callback interface that is used for spontaneous event messages. At the TSPI level, spontaneous events are reported through the Line_Event and Phone_Event callback procedures.


Target Platform Windows
Header tspi.h

See also