MDCID (24-byte bit string)

Correlation identifier.

This is a byte string that the application can use to relate one message to another, or to relate the message to other work that the application is performing. The correlation identifier is a permanent property of the message, and persists across restarts of the queue manager. Because the correlation identifier is a byte string and not a character string, the correlation identifier is not converted between character sets when the message flows from one queue manager to another.

For the MQPUT and MQPUT1 calls, the application can specify any value. The queue manager transmits this value with the message and delivers it to the application that issues the get request for the message.

If the application specifies PMNCID, the queue manager generates a unique correlation identifier which is sent with the message, and also returned to the sending application on output from the MQPUT or MQPUT1 call.

When the queue manager or a message channel agent generates a report message, it sets the MDCID field in the way specified by the MDREP field of the original message, either ROCMTC or ROPCI. Applications which generate report messages should also do this.

For the MQGET call, MDCID is one of the five fields that can be used to select a particular message to be retrieved from the queue. See the description of the MDMID field for details of how to specify values for this field.

Specifying CINONE as the correlation identifier has the same effect as not specifying MOCORI, that is, any correlation identifier will match.

If the GMMUC option is specified in the GMO parameter on the MQGET call, this field is ignored.

On return from an MQGET call, the MDCID field is set to the correlation identifier of the message returned (if any).

The following special values may be used:

CINONE

No correlation identifier is specified.

The value is binary zero for the length of the field.

CINEWS

Message is the start of a new session.

This value is recognized by the CICS bridge as indicating the start of a new session, that is, the start of a new sequence of messages.

For the MQGET call, this is an input/output field. For the MQPUT and MQPUT1 calls, this is an input field if PMNCID is not specified, and an output field if PMNCID is specified. The length of this field is given by LNCID. The initial value of this field is CINONE.