Đang chuẩn bị nút TẢI XUỐNG, xin hãy chờ
Tải xuống
Chương 7 - CPU scheduling. Bài giảng gồm có những nội dung chính sau: Multiprocessors, multicomputers, distributed systems, multiprocessor systems, multiprocessor hardware, multiprocessor OS types. | Chapter 7. Deadlock OBJECTIVES A process requests resources; and if the resources are not available at that time, the process enters a waiting state. Sometimes, a waiting process is never again able to change state, because the resources it has requested are held by other waiting processes. This situation is called a deadlock. To develop a description of deadlocks, which prevent sets of concurrent processes from completing their tasks To present a number of different methods that an operating system can use for preventing or avoiding deadlocks in a computer system. 9.1. System Model A system consists of a finite number of resources to be distributed among a number of competing processes. The resources are partitioned into several types, each consisting of some number of identical instances. Memory space, CPU cycles, files, and I/O devices (such as printers and DVD drives) are examples of resource types. If a system has two CPUs, then the resource type CPU has two instances. If a process requests an instance of a resource type, the allocation of any instance of the type will satisfy the request. If it will not, then the instances are not identical, and the resource type classes have not been defined properly. A process must request a resource before using it and must release the resource after using it. A process may request as many resources as it requires to carry out its designated task. Obviously, the number of resources requested may not exceed the total number of resources available in the system. Under the normal mode of operation, a process may utilize a resource in only the following sequence: 1. Request. If the request cannot be granted immediately (for example, if the resource is being used by another process), then the requesting process must wait until it can acquire the resource. 2. Use. The process can operate on the resource (for example, if the resource is a printer, the process can print on the printer). 3. Release. The process releases the . | Chapter 7. Deadlock OBJECTIVES A process requests resources; and if the resources are not available at that time, the process enters a waiting state. Sometimes, a waiting process is never again able to change state, because the resources it has requested are held by other waiting processes. This situation is called a deadlock. To develop a description of deadlocks, which prevent sets of concurrent processes from completing their tasks To present a number of different methods that an operating system can use for preventing or avoiding deadlocks in a computer system. 9.1. System Model A system consists of a finite number of resources to be distributed among a number of competing processes. The resources are partitioned into several types, each consisting of some number of identical instances. Memory space, CPU cycles, files, and I/O devices (such as printers and DVD drives) are examples of resource types. If a system has two CPUs, then the resource type CPU has two instances. If a .
