本文概述

• Java
• Python3
• C#

先决条件–
磁盘调度算法
给定一系列磁盘磁道编号和初始磁头位置, 我们的任务是查找为访问所有请求的磁道而执行的查找操作总数
最短搜寻时间优先(SSTF)
是使用磁盘调度算法的。
最短搜寻时间优先(SSTF)–
基本思想是, 应首先维修更靠近当前磁盘磁头位置的轨道, 以便
最小化搜寻操作
.
最短搜寻时间优先(SSTF)的优势–

1. 性能优于FCFS调度算法。
2. 它提供了更好的吞吐量。
3. 此算法用于批处理系统, 在该系统中, 吞吐量更为重要。
4. 它的平均响应时间和等待时间更少。

最短搜索时间优先(SSTF)的缺点–

1. 对于某些请求, 可能会出现饥饿, 因为它容易达到请求且忽略了遥远的过程。
2. 由于响应时间差异很大, 因此缺乏可预测性。
3. 切换方向会使事情变慢。

算法–

1. 让Request数组表示一个数组, 该数组存储已请求的曲目的索引。 "磁头"是磁盘磁头的位置。
2. 找到请求数组中所有磁迹到头部的正距离。
3. 从请求的阵列中找到一条尚未被访问/维修且距头部最小距离的轨道。
4. 以此距离增加总寻道数。
5. 当前服务的轨道位置现在变为新的头位置。
6. 转到步骤2, 直到未维修请求数组中的所有轨道。

示例–
请求顺序= {176, 79, 34, 60, 92, 11, 41, 114}
初始头部位置= 50
下表显示了使用SSTF服务请求的曲目的顺序。

文章图片
【如何实现SSTF磁盘调度算法程序（）】因此, 总寻道数计算为：

= (50-41)+(41-34)+(34-11)+(60-11)+(79-60)+(92-79)+(114-92)+(176-114)= 204

实施–
SSTF的实现如下。请注意, 我们已使节点类具有2个成员。 "距离"用于存储头部和轨道位置之间的距离。 " accessed"是一个布尔变量, 它指示磁盘磁头之前是否已经访问过/维护过磁道。
Java

class node {// represent difference between // head position and track number int distance = 0 ; // true if track has been accessed boolean accessed = false ; }public class SSTF {// Calculates difference of each // track number with the head position public static void calculateDifference( int queue[], int head, node diff[]){ for ( int i = 0 ; i < diff.length; i++) diff[i].distance = Math.abs(queue[i] - head); }// find unaccessed track // which is at minimum distance from head public static int findMin(node diff[]) { int index = - 1 , minimum = Integer.MAX_VALUE; for ( int i = 0 ; i < diff.length; i++) { if (!diff[i].accessed & & minimum > diff[i].distance) {minimum = diff[i].distance; index = i; } } return index; }public static void shortestSeekTimeFirst( int request[], int head){ if (request.length == 0 ) return ; // create array of objects of class node node diff[] = new node[request.length]; // initialize array for ( int i = 0 ; i < diff.length; i++) diff[i] = new node(); // count total number of seek operation int seek_count = 0 ; // stores sequence in which disk access is done int [] seek_sequence = new int [request.length + 1 ]; for ( int i = 0 ; i < request.length; i++) {seek_sequence[i] = head; calculateDifference(request, head, diff); int index = findMin(diff); diff[index].accessed = true ; // increase the total count seek_count += diff[index].distance; // accessed track is now new head head = request[index]; }// for last accessed track seek_sequence[seek_sequence.length - 1 ] = head; System.out.println( "Total number of seek operations = " + seek_count); System.out.println( "Seek Sequence is" ); // print the sequence for ( int i = 0 ; i < seek_sequence.length; i++) System.out.println(seek_sequence[i]); }public static void main(String[] args) { // request array int arr[] = { 176 , 79 , 34 , 60 , 92 , 11 , 41 , 114 }; shortestSeekTimeFirst(arr, 50 ); } }

Python3

# Python3 program for implementation of # SSTF disk scheduling # Calculates difference of each # track number with the head position def calculateDifference(queue, head, diff): for i in range ( len (diff)): diff[i][ 0 ] = abs (queue[i] - head) # find unaccessed track which is # at minimum distance from head def findMin(diff): index = - 1 minimum = 999999999for i in range ( len (diff)): if ( not diff[i][ 1 ] and minimum > diff[i][ 0 ]): minimum = diff[i][ 0 ] index = i return index def shortestSeekTimeFirst(request, head): if ( len (request) = = 0 ): returnl = len (request) diff = [ 0 ] * l# initialize array for i in range (l): diff[i] = [ 0 , 0 ]# count total number of seek operation seek_count = 0# stores sequence in which disk # access is done seek_sequence = [ 0 ] * (l + 1 ) for i in range (l): seek_sequence[i] = head calculateDifference(request, head, diff) index = findMin(diff) diff[index][ 1 ] = True# increase the total count seek_count + = diff[index][ 0 ] # accessed track is now new head head = request[index] # for last accessed track seek_sequence[ len (seek_sequence) - 1 ] = head print ( "Total number of seek operations =" , seek_count) print ( "Seek Sequence is" ) # print the sequence for i in range (l + 1 ): print (seek_sequence[i]) # Driver code if __name__ = = "__main__" :# request array proc = [ 176 , 79 , 34 , 60 , 92 , 11 , 41 , 114 ] shortestSeekTimeFirst(proc, 50 )# This code is contributed by # Shubham Singh(SHUBHAMSINGH10)

C#

// C# program for implementation of FCFS // scheduling using System; public class node {// represent difference between // head position and track number public int distance = 0; // true if track has been accessed public Boolean accessed = false ; }public class SSTF {// Calculates difference of each // track number with the head position public static void calculateDifference( int []queue, int head, node []diff){ for ( int i = 0; i < diff.Length; i++) diff[i].distance = Math.Abs(queue[i] - head); }// find unaccessed track // which is at minimum distance from head public static int findMin(node []diff) { int index = -1, minimum = int .MaxValue; for ( int i = 0; i < diff.Length; i++) { if (!diff[i].accessed & & minimum > diff[i].distance) {minimum = diff[i].distance; index = i; } } return index; }public static void shortestSeekTimeFirst( int []request, int head) { if (request.Length == 0) return ; // create array of objects of class node node []diff = new node[request.Length]; // initialize array for ( int i = 0; i < diff.Length; i++) diff[i] = new node(); // count total number of seek operation int seek_count = 0; // stores sequence in which disk access is done int [] seek_sequence = new int [request.Length + 1]; for ( int i = 0; i < request.Length; i++) {seek_sequence[i] = head; calculateDifference(request, head, diff); int index = findMin(diff); diff[index].accessed = true ; // increase the total count seek_count += diff[index].distance; // accessed track is now new head head = request[index]; }// for last accessed track seek_sequence[seek_sequence.Length - 1] = head; Console.WriteLine( "Total number of seek operations = " + seek_count); Console.WriteLine( "Seek Sequence is" ); // print the sequence for ( int i = 0; i < seek_sequence.Length; i++) Console.WriteLine(seek_sequence[i]); }// Driver code public static void Main(String[] args) { // request array int []arr = { 176, 79, 34, 60, 92, 11, 41, 114 }; shortestSeekTimeFirst(arr, 50); } }// This code contributed by Rajput-Ji

输出如下：

Total number of seek operations = 204Seek Sequence is50413411607992114176

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