Scheduling algorithms

Scheduling algorithms是指操作系统中用于决定进程执行顺序的算法。常见的调度算法有先来先服务（FCFS）、最短作业优先（SJF）、优先级调度、时间片轮转等。

其中，FCFS算法是按照进程到达的先后顺序进行调度，即先到先服务；SJF算法是按照进程需要的CPU时间进行调度，即短作业优先；优先级调度是按照进程的优先级进行调度，优先级高的进程先执行；时间片轮转是按照时间片大小进行调度，每个进程执行一个时间片后切换到下一个进程。

不同的调度算法适用于不同的场景和需求，需要根据具体情况进行选择和调整。

相关问题

Write a C program that implements the following disk-scheduling algorithms: a. FCFS b. SSTF c. SCAN d. C-SCAN e. LOOK f. C-LOOK Your program will service a disk with 5,000 cylinders numbered 0 to 4,999. The program will generate a random series of 1,000 cylinder requests and service them according to each of the algorithms listed above. The program will be passed the initial position of the disk head (as a parameter on the command line) and report the total amount of head movement required by each algorithm.

Sure, here's a sample C program that implements the disk-scheduling algorithms you mentioned:

#include <stdio.h>
#include <stdlib.h>
#include <stdbool.h>

#define CYLINDERS 5000
#define REQUESTS 1000

// Struct to represent a disk request
typedef struct {
    int cylinder;
    bool visited;
} request;

// Function to generate random cylinder requests
void generateRequests(request* queue) {
    for (int i = 0; i < REQUESTS; i++) {
        queue[i].cylinder = rand() % CYLINDERS;
        queue[i].visited = false;
    }
}

// FCFS algorithm
int fcfs(request* queue, int head) {
    int totalMovement = 0;
    for (int i = 0; i < REQUESTS; i++) {
        totalMovement += abs(head - queue[i].cylinder);
        head = queue[i].cylinder;
    }
    return totalMovement;
}

// SSTF algorithm
int sstf(request* queue, int head) {
    int totalMovement = 0;
    for (int i = 0; i < REQUESTS; i++) {
        int minDistance = CYLINDERS;
        int minIndex = -1;
        for (int j = 0; j < REQUESTS; j++) {
            if (!queue[j].visited) {
                int distance = abs(head - queue[j].cylinder);
                if (distance < minDistance) {
                    minDistance = distance;
                    minIndex = j;
                }
            }
        }
        if (minIndex != -1) {
            totalMovement += minDistance;
            head = queue[minIndex].cylinder;
            queue[minIndex].visited = true;
        }
    }
    return totalMovement;
}

// SCAN algorithm
int scan(request* queue, int head) {
    int totalMovement = 0;
    int direction = 1; // 1 for up, -1 for down
    int currentIndex = -1;
    for (int i = 0; i < REQUESTS; i++) {
        if (queue[i].cylinder == head) {
            currentIndex = i;
            break;
        }
    }
    if (currentIndex == -1) {
        // Insert head into queue
        for (int i = 0; i < REQUESTS; i++) {
            if (head < queue[i].cylinder) {
                for (int j = REQUESTS - 1; j > i; j--) {
                    queue[j] = queue[j-1];
                }
                queue[i].cylinder = head;
                queue[i].visited = true;
                currentIndex = i;
                break;
            }
        }
    }
    for (int i = currentIndex; i >= 0 && i < REQUESTS; i += direction) {
        if (!queue[i].visited) {
            totalMovement += abs(head - queue[i].cylinder);
            head = queue[i].cylinder;
            queue[i].visited = true;
        }
        if (i == 0 || i == REQUESTS - 1) {
            direction = -direction;
        }
    }
    return totalMovement;
}

// C-SCAN algorithm
int cscan(request* queue, int head) {
    int totalMovement = 0;
    int currentIndex = -1;
    for (int i = 0; i < REQUESTS; i++) {
        if (queue[i].cylinder == head) {
            currentIndex = i;
            break;
        }
    }
    if (currentIndex == -1) {
        // Insert head into queue
        for (int i = 0; i < REQUESTS; i++) {
            if (head < queue[i].cylinder) {
                for (int j = REQUESTS - 1; j > i; j--) {
                    queue[j] = queue[j-1];
                }
                queue[i].cylinder = head;
                queue[i].visited = true;
                currentIndex = i;
                break;
            }
        }
    }
    // Service requests in one direction
    for (int i = currentIndex; i >= 0; i--) {
        if (!queue[i].visited) {
            totalMovement += abs(head - queue[i].cylinder);
            head = queue[i].cylinder;
            queue[i].visited = true;
        }
    }
    totalMovement += head; // Head movement to go to the end
    head = 0;
    // Service requests in the other direction
    for (int i = REQUESTS - 1; i > currentIndex; i--) {
        if (!queue[i].visited) {
            totalMovement += abs(head - queue[i].cylinder);
            head = queue[i].cylinder;
            queue[i].visited = true;
        }
    }
    return totalMovement;
}

// LOOK algorithm
int look(request* queue, int head) {
    int totalMovement = 0;
    int direction = 1; // 1 for up, -1 for down
    int currentIndex = -1;
    for (int i = 0; i < REQUESTS; i++) {
        if (queue[i].cylinder == head) {
            currentIndex = i;
            break;
        }
    }
    if (currentIndex == -1) {
        // Insert head into queue
        for (int i = 0; i < REQUESTS; i++) {
            if (head < queue[i].cylinder) {
                for (int j = REQUESTS - 1; j > i; j--) {
                    queue[j] = queue[j-1];
                }
                queue[i].cylinder = head;
                queue[i].visited = true;
                currentIndex = i;
                break;
            }
        }
    }
    for (int i = currentIndex; i >= 0 && i < REQUESTS; i += direction) {
        if (!queue[i].visited) {
            totalMovement += abs(head - queue[i].cylinder);
            head = queue[i].cylinder;
            queue[i].visited = true;
        }
        if (i == 0 || i == REQUESTS - 1) {
            direction = -direction;
        }
    }
    return totalMovement;
}

// C-LOOK algorithm
int clook(request* queue, int head) {
    int totalMovement = 0;
    int currentIndex = -1;
    for (int i = 0; i < REQUESTS; i++) {
        if (queue[i].cylinder == head) {
            currentIndex = i;
            break;
        }
    }
    if (currentIndex == -1) {
        // Insert head into queue
        for (int i = 0; i < REQUESTS; i++) {
            if (head < queue[i].cylinder) {
                for (int j = REQUESTS - 1; j > i; j--) {
                    queue[j] = queue[j-1];
                }
                queue[i].cylinder = head;
                queue[i].visited = true;
                currentIndex = i;
                break;
            }
        }
    }
    // Service requests in one direction
    for (int i = currentIndex; i >= 0; i--) {
        if (!queue[i].visited) {
            totalMovement += abs(head - queue[i].cylinder);
            head = queue[i].cylinder;
            queue[i].visited = true;
        }
    }
    // Service requests in the other direction
    for (int i = REQUESTS - 1; i > currentIndex; i--) {
        if (!queue[i].visited) {
            totalMovement += abs(head - queue[i].cylinder);
            head = queue[i].cylinder;
            queue[i].visited = true;
        }
    }
    return totalMovement;
}

int main(int argc, char* argv[]) {
    if (argc < 2) {
        printf("Usage: %s <initial position>\n", argv[0]);
        return 1;
    }
    int initial = atoi(argv[1]);
    if (initial < 0 || initial >= CYLINDERS) {
        printf("Initial position must be between 0 and %d\n", CYLINDERS - 1);
        return 1;
    }

    request queue[REQUESTS];
    generateRequests(queue);

    printf("FCFS: %d\n", fcfs(queue, initial));
    for (int i = 0; i < REQUESTS; i++) {
        queue[i].visited = false;
    }
    printf("SSTF: %d\n", sstf(queue, initial));
    for (int i = 0; i < REQUESTS; i++) {
        queue[i].visited = false;
    }
    printf("SCAN: %d\n", scan(queue, initial));
    for (int i = 0; i < REQUESTS; i++) {
        queue[i].visited = false;
    }
    printf("C-SCAN: %d\n", cscan(queue, initial));
    for (int i = 0; i < REQUESTS; i++) {
        queue[i].visited = false;
    }
    printf("LOOK: %d\n", look(queue, initial));
    for (int i = 0; i < REQUESTS; i++) {
        queue[i].visited = false;
    }
    printf("C-LOOK: %d\n", clook(queue, initial));

    return 0;
}

To compile and run the program, you can use the following commands:

$ gcc disk-scheduling.c -o disk-scheduling
$ ./disk-scheduling <initial position>

Replace `<initial position>` with the desired starting position of the disk head. The program will generate a random series of 1,000 cylinder requests and service them according to each of the algorithms listed above, reporting the total amount of head movement required by each algorithm.

coflow scheduling frameworks

Coflow scheduling frameworks are used to manage the communication patterns between different stages of a data processing job. These frameworks help in optimizing the overall performance of the job by minimizing the communication delays and improving the data transfer rates. Some popular coflow scheduling frameworks are:

1. Apache Tez: It is a general-purpose data processing framework that supports efficient coflow scheduling. It uses a DAG-based execution model and can handle complex data processing jobs with ease.

2. Apache Flink: It is a distributed data processing framework that supports batch and stream processing. It provides a built-in scheduling algorithm that optimizes the execution of coflows.

3. Apache Spark: It is a popular data processing framework that supports in-memory processing and can handle large-scale data processing jobs. It provides a built-in scheduler that optimizes the execution of coflows.

4. Apache Hadoop: It is a distributed data processing framework that provides support for coflow scheduling through its YARN resource manager. It uses a fair scheduler that allocates resources based on the coflow requirements.

5. Coflowsim: It is a simulation-based coflow scheduling framework that allows users to test different scheduling algorithms and evaluate their performance on different network topologies. It provides a user-friendly interface and supports various scheduling algorithms.