Oberon || Library || Module Index || Search Engine || Definition || Module

Ulm's Oberon Library:
StreamConditions

NAME

SYNOPSIS

CONST read = 0; write = 1; (* operations *)
TYPE Operation = SHORTINT; (* read or write *)
TYPE CreateConditionMessage =
   RECORD
      (Streams.Message)
      (* in-parameters *)
      operation: Operation; (* read or write *)
      (* out-parameters *)
      condition: Conditions.Condition; (* return value *)
      stream: Streams.Stream; (* message processed for this stream *)
      msgProcessed: BOOLEAN; (* initially FALSE; has to be set to TRUE *)
   END;
TYPE TestConditionMessage =
   RECORD
      (Streams.Message)
      (* in-parameters *)
      operation: Operation; (* read or write *)
      errors: RelatedEvents.Object; (* relate errors to this object *)
      (* out-parameters *)
      wouldblock: BOOLEAN;
      msgProcessed: BOOLEAN;
   END;



CONST msgFailed = 0;
CONST invalidOp = 1;
CONST errorcodes = 2;
TYPE ErrorEvent = POINTER TO ErrorEventRec;
TYPE ErrorEventRec =
   RECORD
      (Events.EventRec)
      errorcode: SHORTINT;
   END;
VAR errormsg: ARRAY errorcodes OF Events.Message;
VAR error: Events.EventType;



PROCEDURE Create(VAR condition: Conditions.Condition;
                 s: Streams.Stream; operation: Operation);

DESCRIPTION

Stream conditions must be supported by the underlying stream implementation. StreamConditions uses stream messages to communicate with the stream implementation:

CreateConditionMessage

asks the underlying implementation to create a condition. The newly created condition is to be returned in condition. Further, stream is to be set to the stream. Because the message may be passed through some other stream implementations it is possible that this is a different stream. msgProcessed must be set to TRUE, otherwise StreamConditions assumes that the implementation does not support stream conditions.
In case of buffered streams it is important that the implementation does not forget to check the buffer status by use of the appropiate routines of Streams.
The underlying implementation is free to set condition to NIL. StreamConditions creates then a condition of its own and assumes that the stream implementation is able to process messages of type TestConditionMessage.

TestConditionMessage

requests the stream implementation to test the condition: wouldblock is to be set to TRUE if an operation would cause the process or task to be blocked or in case of errors. Any errors are to be related to errors instead to the stream. Again, msgProcessed must be set to TRUE to indicate that the message has been processed.

Create creates a condition which allows the process or task to wait until the stream becomes ready for the given operation. condition is set to NIL if stream conditions are not supported for the underlying stream implementation.

DIAGNOSTICS

msgFailed

indicates that a message was returned unprocessed.

invalidOp

an invalid operation was given to Create (neither read nor write).

SEE ALSO

Conditions

interface for conditions

Streams

streams interface

Oberon || Library || Module Index || Search Engine || Definition || Module