Order of Command Execution

Many factors control the order of command execution. JES3 cannot guarantee the order in which commands are executed for the following reasons:

Multiple commands entered through a single command issuance (eg. stacked) will be parsed from the end until a command delimiter (eg. semi-colon) is found and re-issued to be processed by automation and MPF/message exits individually.
JES3 FCT dispatching priorities will cause some commands to be executed before others.
Console appendages written for each Dynamic Support Program (DSP) may process commands in any order.
Multiple FCTs may exist to process a certain type of command; this affects the order commands are executed. For example, multiple MODOSFCT FCTs can be active at the same time processing *MODIFY,U commands occurs.
JES3 or MVS™ command exit processing may affect the time any single command takes to execute.
Depending on if any JES3 spool I/O is required to process the command will affect the time any single command takes to execute. Many JES3 commands result in calls to the Work-To-Do-Driver (WTDDRVR) FCT, which processes commands which require JES3 spool I/O.
Long running commands based on job queue searches and JES3 spool I/O which may be necessary to access job information should not delay other critical JES3 command processing.
Non-JES3 commands processed by MVS or other subsystems will execute under other programs beyond JES3's control. JES3 is not designed to synchronize the order of command execution between JES3 and non-JES3 commands.

IBM® recommends that customers use message-based automation (for example, MPF command exits) if feasible, or use automation to setup time delays as appropriate between critical commands, whenever order of command execution is important to their operations. In these cases, automation should be used to ensure any single command has finished execution before issuing the next command in any critical sequence.