Throughout the discussion about sending a message, there are a number of IBM recommendations and cautions; they are summarized here:

• Do not send REQTYPE=SYNC messages under the JES main task.
• Be certain that the receiver of a message can process it. If, for example, two members send each other a REQTYPE=SYNC message, there is the possibility that the two will create a deadlock situation and each wait forever to receive the acknowledgement.
• Use the minimal level of REQTYPE= messaging as required to meet your multisystem recovery needs. The message types are listed here from least (no) recovery to most recovery; as the recovery capability increases, so does the potential for system performance impact.
  1. COMM
  2. ASYNC
  3. ASYNCACK and SYNC
• If a member detaches from JES XCF, be certain to clear the group token field in your application program; it will no longer be valid.