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3.4.1 Concurrent Execution of Commands

 






   When executing commands in the background and foreground concurrently, you 
   should be aware that allocation of a data set both in the foreground and 
   the background might not be successful. If a data set has been allocated 
   (foreground or background mode) with a disposition of OLD, MOD, or NEW, it 
   cannot be allocated in the opposite mode by the ALLOCATE command or any 
   other command processor. For example, the ALLOCATE command, issued in the 
   background for a data set in use in the foreground, will issue an error 
   message that the data set is already in use. Any command remaining in the 
   job stream is processed. 



   If a user's LOGON procedure allocates a data set with a disposition of 
   NEW, MOD, or OLD, a background job specifying the same LOGON procedure 
   will not execute until the user logs off or frees the data set in the 
   foreground.  Similarly, if a background job is executing and the user 
   attempts to log on a terminal with the same LOGON procedure, the logon 
   attempt fails. 





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