Priority ceiling protocol

There are two variants of the protocol: Original Ceiling Priority Protocol (OCPP) and Immediate Ceiling Priority Protocol (ICPP). The worst-case behaviour of the two ceiling schemes is identical from a scheduling view point. Both variants work by temporarily raising the priorities of tasks. In OCPP, a task X's priority is raised when a higher-priority task Y tries to acquire a resource that X has locked. The task X's priority is then raised to the highest priority of any such Y that had been blocked by itself, ensuring that task X quickly finishes its critical section and unlocks the resource. A task is only allowed to lock a resource if its dynamic priority is higher than the priority ceilings of all resources locked by other tasks. Otherwise the task becomes blocked, waiting for the resource. It is also known as "Highest Locker's Priority Protocol" (HLP). ==See also==