17. A trap semaphore as recited in claim 16 including fifth means responsive to said event variable for detecting said first type event occurrence posted on said event variable device.
17. A trap semaphore as recited in claim 16 including fifth means responsive to said event variable for detecting said first type event occurrence posted on said event variable device. 18. A trap semaphore as recited in claim 17 including sixth means responsive to said trap event variable for detecting said second type event occurrence posted on said trap event variable device.