The priority ceiling protocol is a real-time scheduling and resource-access protocol that prevents unbounded priority inversion and deadlock among tasks sharing mutually exclusive resources. Each resource is assigned a ceiling equal to the highest priority of any task that may lock it, and a task may acquire a resource only if its priority exceeds the ceilings of all currently locked resources. It bounds blocking time, enabling provable schedulability in hard real-time systems.
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- By assigning each shared resource a ceiling priority and restricting acquisition relative to active ceilings, the protocol guarantees that a high-priority task is blocked by lower-priority tasks for at most one critical section. This bound makes worst-case blocking analysable, a prerequisite for response-time analysis in safety-critical and embedded real-time systems.