A conditional abortable priority ceiling protocol for scheduling mixed real-time tasks

Priority Ceiling Protocol (PCP) is a well-known resource access protocol for hard real-time systems. However, it has a problem of ceiling blocking which imposes a great hindrance to task scheduling in mixed real-time systems where tasks may have different criticality. In this paper, a new resource access protocol called the Conditional Abortable Priority Ceiling Protocol (CA-PCP) is proposed. It resolves the problem of ceiling blocking by incorporating a conditional abort scheme into the PCP. The new protocol inherits all the desirable properties of the PCP and the Ceiling Abort Protocol (CAP) which is yet another modification of the PCP. In the proposed protocol, a condition is defined to control the abort of a job so that the schedulability of the system will not be affected. Performance study has been done to compare the CA-PCP with the PCP. The results indicate that CA-PCP can significantly improve the performance of a system if the lengths of the abortable critical sections are well chosen.