Requirements for Mutual Exclusion (互斥的要求) 1. Only one process at a time is allowed in the critical section for a resource(一次仅 允许一个进程进入临界区) 2. A process that halts in its non-critical section must do so without interfering with other processes((处于非临界区的进程不 能干预其它进程) 3. no deadlock or starvation
Requirements for Mutual Exclusion (互斥的要求) 4. a process must not be delayed access to a critical section when there is no other process using it(当没有进程在临界区时应立即进入) 5. No assumptions are made about relative process speeds or number of processors(对相关 进程的速度和处理机的数目没有任何要求和限制) 6. A process remains inside its critical section for a finite time only(一个进程驻留在它的临界区中的 时间必须是有限的确)
Requirements for Mutual Exclusion (互斥的要求) 空闲让进 则等待 有限等待 让权等待
Approaches of Mutual Exclusion (互斥的方法) Software Approaches(软件方法) Hardware Support Semaphores Monitors essage Passing
5.2 Software Approaches Memory access level Access to the same location in main memory are serialized by some sort of memory arbiter Dekkers algorithm · Peterson’ S Algorithn