聊城大学计算机学院计算机操作系统（1）英文课件 Chapter5.ppt

Concurrency: Mutual Exclusion and Synchronization Chapter 5 Concurrency Multiple applications Structured applications Operating system structure Concurrency Difficulties of Concurrency Sharing of global resources Operating system managing the allocation of resources optimally Difficult to locate programming errors Currency Communication among processes Sharing resources Synchronization of multiple processes Allocation of processor time Concurrency Multiple applications Multiprogramming Structured application Application can be a set of concurrent processes Operating-system structure Operating system is a set of processes or threads A Simple Example void echo() { chin = getchar(); chout = chin; putchar(chout); } A Simple Example Process P1 Process P2 . . chin = getchar(); . . chin = getchar(); chout = chin; chout = chin; putchar(chout); . . putchar(chout); . . Operating System Concerns Keep track of various processes Allocate and deallocate resources Processor time Memory Files I/O devices Protect data and resources Output of process must be independent of the speed of execution of other concurrent processes Process Interaction Processes unaware of each other Processes indirectly aware of each other Process directly aware of each other Competition Among Processes for Resources Mutual Exclusion Critical sections Only one program at a time is allowed in its critical section Example only one process at a time is allowed to send command to the printer Deadlock Starvation Requirements for Mutual Exclusion Only one process at a time is allowed in the critical section for a resource A process that halts in its noncritical section must do so without interfering with other processes No deadlock or starvation Requirements for Mutual Exclusion A process must not be delayed access to a critical section when there is no other process using it No assumptions are made about relative process speeds or number of processes A process remains inside i