短作业优先的作业调度-操作系统课程设计.doc

摘 要 作业调度是对成批进入系统的用户作业，根据作业控制块的信息，按一定的策略选取若干个作业使它们可以去获得处理器运行的一项工作。而对每个用户来说总希望自己的作业的周转时间是最小的，短作业优先（SJF）便是其中一种调度方法。 本设计是为了加深对作业概念的理解，掌握短作业优先（SJF）算法，深入了解批处理系统如何组织作业、管理作业和调度作业，了解作业控制块的作用，以及作业控制块的内容和组织方式。 为了将系统中的作业组织起来，需要为每个进入系统的作业建立档案以记录和作业相关的信息，例如作业名、作业所需资源、作业执行时间、作业进入系统的时间、作业信息在存储器中的位置、指向下一个作业控制块的指针等信息。这个记录作业相关信息的数据块称为作业控制块（JCB），并将系统中等待作业调度的作业控制块组织成一个队列，这个队列称为后备队列。一个作业全部信息进入系统后，就为其建立作业控制块，并挂入后备队列。当进行作业调度时，从后备队列中查找选择作业。 在从后备队列中查找选择作业是，先根据作业控制块中的信息，选中一个短作业，也就是执行时间最短的作业，将它们调入内存运行。 关键词 ：作业; 调度; 短作业优先; SJF; JCB Abstract Batch job scheduling problem is to enter the system according to the user, the job control block of information, according to certain strategy selection several assignments that they can go to obtain a processor runs. For each user is always hope their job cycle time is the smallest, short j (SJF) which is the preferred method of a kind of scheduling. This design is to deepen the understanding of the concept of job assignments, short job first (SJF) algorithm is, in-depth understanding of how the system of batch management and organization, scheduling, understand the job assignments, as well as the job control blocks of content and organization. In order to organize the assignment system for everyone to enter the system to establish archives of job assignments and related information recorded, for example, job assignments, resources, work into execution time of time, information system in memory of job assignments, pointing to a position job control block etc. The record of the information data block job assignments job control blocks (called), and the system JCB waiting in the job assignments scheduling job control block into a queue, the queue as backup queue. A full information into a system for its establishment, operation job control block, and hung the backup queue. When scheduling problem, from the backlog queue for choice. From the backlog queue for job first choice, according to the information and job control block a short assignment,