Using multiple inputs

If you want your stage to handle multiple inputs, there are some special considerations.

Your code needs to ensure the following:

• The stage only tries to access a column when there are records available. It should not try to access a column after all records have been read (use the inputDone() macro to check), and should not attempt to access a column unless either Auto Read is enabled on the link or an explicit read record has been performed.
• The reading of records is terminated immediately after all the required records have been read from it. In the case of a port with Auto Read disabled, the code must determine when all required records have been read and call the endLoop() macro.

In most cases you might keep Auto Read enabled when you are using multiple inputs, this minimizes the need for explicit control in your code. But there are circumstances when this is not appropriate. The following paragraphs describes some common scenarios:

Using auto read for all inputs

All ports have Auto Read enabled and so all record reads are handled automatically. You need to code for Per-record loop such that each time it accesses a column on any input it first uses the inputDone() macro to determine if there are any more records.

This method is fine if you want your stage to read a record from every link, every time round the loop.

Using inputs with auto read enabled for some and disabled for others

You define one (or possibly more) inputs as Auto Read, and the rest with Auto Read disabled. You code the stage in such a way as the processing of records from the Auto Read input drives the processing of the other inputs. Each time round the loop, your code should call inputDone() on the Auto Read input and call exitLoop() to complete the actions of the stage.

This method is fine where you process a record from the Auto Read input every time around the loop, and then process records from one or more of the other inputs depending on the results of processing the Auto Read record.

Using inputs with auto read disabled

Your code must explicitly perform all record reads. You should define Per-Loop code which calls readRecord() once for each input to start processing. Your Per-record code should call inputDone() for every input each time round the loop to determine if a record was read on the most recent readRecord(), and if it did, call readRecord() again for that input. When all inputs run out of records, the Per-Loop code should exit.

This method is intended where you want explicit control over how each input is treated.