In a dynamic priority system the priorities of the periodic tasks change with time while the resources required by each task remain constant. Hence, the priority ceilings of the resources may change with time. Consider a system with two tasks Tasks T1 (2, 0.9), T2 (5, 2.3) executed in deadline driven system as below.
In its first two periods from time 0 to 4. Tl has priority 1 while T2 has priority 2, but from time 4 to 5 T2 has priority 1 and Tl has priority 2. Suppose that the task Tl requires a resource X while T2 does not. The priority ceiling of X is 1 from time 0 to 4 and becomes 2 from time 4 to 5 and so on .For dynamic systems, we can use the priority ceiling protocol to control resource accesses provided we update the priority ceiling of each resource and the ceiling of the system each time task priorities change.