上海交通大学：《操作系统 Operating System》课程教学资源（课件讲稿）OS-deadlock_Lec15

OPERATING SYSTEMS 1 龚玲 lgong@sjtu.edu.cn

OPERATING SYSTEMS 龚玲 lgong@sjtu.edu.cn 1

REVIEW o Semaphores o http://wenku.baidu.com/course/study/77f1dcccda38376ba flfae94#665ea0c7aa00b52acfc7ca94

REVIEW  Semaphores  http://wenku.baidu.com/course/study/77f1dcccda38376ba f1fae94#665ea0c7aa00b52acfc7ca94

Goals for today o Monitors o Deadlock

Goals for today  Monitors  Deadlock

Monitors o A high-level abstraction that provides a convenient and effective mechanism for process synchronization o Only one process may be active within the monitor at a time

Monitors  A high-level abstraction that provides a convenient and effective mechanism for process synchronization  Only one process may be active within the monitor at a time

Syntax of a monitor monitor monitor name /shared variable declarations initialization code (...) } public P1(··.){ } public P2(···){ } public Pn(···){

Syntax of a Monitor

Schematic view of a Monitor □ entry queue shared data operations initialization code

Schematic view of a Monitor

Condition Variables o Condition x,y; o Two operations on a condition variable: x.wait -a process that invokes the operation is suspended. x.signal (-resumes one of processes (if any) that invoked x.wait

Condition Variables  Condition x, y;  Two operations on a condition variable:  x.wait () – a process that invokes the operation is suspended.  x.signal () – resumes one of processes (if any) that invoked x.wait ()

Monitor with Condition Variables entry queue shared data queues associated with X☐□☐. x,y conditions y+G图 operations initialization code

Monitor with Condition Variables

Chapter 7:Deadlocks o The Deadlock Problem oSystem Model o Deadlock Characterization o Methods for Handling Deadlocks o Deadlock Prevention o Deadlock Avoidance o Deadlock Detection o Recovery from Deadlock

Chapter 7: Deadlocks  The Deadlock Problem  System Model  Deadlock Characterization Methods for Handling Deadlocks  Deadlock Prevention  Deadlock Avoidance  Deadlock Detection  Recovery from Deadlock

Chapter Objectives o To develop a description of deadlocks,which prevent sets of concurrent processes from completing their tasks o To present a number of different methods for preventing or avoiding deadlocks in a computer system

Chapter Objectives  To develop a description of deadlocks, which prevent sets of concurrent processes from completing their tasks  To present a number of different methods for preventing or avoiding deadlocks in a computer system