When you perform request download, the expected behavior is you should see the information message below:
However, sometimes you may see warning message with status Wait instead.
How to research this issue by yourself?
Set a breakpoint on function module SMOF0_INIT_DNL_START which does the main logic of download.
Here the parameter MAX_PARALLEL_PROCESSES is queried. In my system the value is 5, which means at maximum there are FIVE parallel work process allowed to perform middleware download task.
Then line 107 ~ 115 is responsible to calculate how many processes are available to operate on current download task. The result is stored in variable gv_open_processes in line 115.
In my example, the number of free processes is 5 – 5 = 0, as a result the download task could not be started and warning message is raised.
The solution is, either cancel existing running download task in tcode R3AR3,
or maintain a larger value for MAX_PARALLEL_PROCESSES in table SMOFPARSFA: