The easiest way to poll a file would be to reposition to the start and read a record every time the end of file is met. But this is not a good solution as jobs continually polling a file in this way will take far too much CPU and slow the system down. Delay must be introduced. The simplest way is to add a delay job (DLYJOB) every time an end of file condition is met. But DLYJOB is not perfect. The minimum time you can delay a job with it is one second. You can delay a job by only a number of seconds, not a fraction of a second.
One second is fine in most cases, but sometimes, you can't afford to wait for one second and you can't afford not to wait. This is where a C function comes in handy. "pthread_delay_np" delays a thread for a number of nanoseconds! Well, not quite. The IBM manual mentions that it's more useful when you need to delay your thread by thousands of a second rather than nanoseconds, but still, it is a godsend. With it, you may decide to poll your file every tenth of a second. In most cases, this should not be too taxing for your system.This API is written in C and therefore expects parameters in a specific format. Reproducing the timespec format in RPG ILE, I obtained:
D timeSpec ds D seconds 10i 0 D nanoseconds 10i 0 I declared the API as follows: D delay pr 5i 0 extProc('pthread_delay_np') d * value
The API expects a pointer to the timespec definition. It also returns a non-zero value if a problem occurred (which is unlikely if you are passing a valid timespec). Nevertheless, I added monitoring just in case to avoid the system doing no delay whatsoever.
c eval seconds = 0 c eval nanoseconds = 10000000 C eval return = delay(%addr(timeSpec)) c if return <> 0 c callP (e) system('DLYJOB 1') c endIf
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This was first published in March 2005