clear_message — Close a message handle and release all associated resources.
clear_message( : : MessageHandle : )
clear_message closes a message handle
was previously opened with
dequeue_message. Any resources owned by the message, in particular
the tuple or object data stored in the message, will be released.
Multiple message handles can be closed in a single
call, passing them as a tuple to the
The handle(s) must not be used again after being invalidated using
clear_message. Using an invalid handle results in
This operator modifies the state of the following input parameter:
During execution of this operator, access to the value of this parameter must be synchronized if it is used across multiple threads.
MessageHandle(input_control, state is modified) message(-array)
Message handle(s) to be closed.
Number of elements: MessageHandle >= 1
MessageHandle != 0
MessageHandles :=  for idx := 0 to 4 by 1 create_message (MessageHandle) MessageHandles[idx]:= MessageHandle endfor * ...
If the message handle(s) passed to the operator are valid,
clear_message returns 2 (H_MSG_TRUE). Otherwise an exception is raised.
If a tuple of handles is passed and some of them are invalid,
clear_message attempts to clear as many handles from the tuple as
possible before reporting the error.