Actual deadlock Requires Given that the first 3 conditions exist. a sequence of events may occur that lead to the following fourth condition Circular wait a closed chain of processes exists, such that each process holds at least one resource needed by the next process in the chain 16
16 Actual Deadlock Requires … Given that the first 3 conditions exist, a sequence of events may occur that lead to the following fourth condition: • Circular wait – A closed chain of processes exists, such that each process holds at least one resource needed by the next process in the chain
Resource Allocation Graphs of deadlock Ra Ra P1 P2 PI P2 Rb Rb (c) Circular wait (d) No deadlock 17
17 Resource Allocation Graphs of deadlock
Resource Allocation Graphs P1 P2 P3 P4 Ra Rb Re Rd Figure 6.6 Resource Allocation Graph for Figure 6.11 (the traffic deadlock shown in slide 4)
18 Resource Allocation Graphs (the traffic deadlock shown in slide 4)