Cheap Mutual Exclusion

A new method of enforcing mutual exclusion among concurrent processes on uniprocessors running UNIX is presented in this paper. When a process attempts to obtain a lock, no race condition will occur unless the process is preempted. The central idea is that a process can avoid a race condition if preemption is made visible to the process when it is rescheduled. Two possible implementations of this idea are discussed in depth. The proposed solutions do not require special hardware support or disabling of interrupts during a critical section.