C语言中使用共享内存的斐波那契序列

Question

2009-EE-182-Part2.c: In function ‘main’:
2009-EE-182-Part2.c:35:13: error: expected identifier or ‘(’ before ‘->’ token
2009-EE-182-Part2.c:40:22: error: expected identifier or ‘(’ before ‘->’ token
2009-EE-182-Part2.c:41:14: error: expected identifier or ‘(’ before ‘->’ token
2009-EE-182-Part2.c:42:22: error: expected expression before ‘shared_data’
2009-EE-182-Part2.c:44:15: error: expected identifier or ‘(’ before ‘->’ token
2009-EE-182-Part2.c:54:15: error: expected expression before ‘shared_data’
2009-EE-182-Part2.c:55:19: error: expected expression before ‘shared_data’

代码是：

# include <stdio.h>
# include <sys/shm.h>
# include <sys/stat.h>
# include <sys/types.h>
# include <unistd.h>
# define MAX_SEQUENCE 10

typedef struct{
long fib_sequence[MAX_SEQUENCE];
int sequence_size;
} shared_data;

char* shared_memory; /* a pointer to the shared memory segment */

int main()
{
int a,b,m,n,i,j;
a=0; b=1;
printf("Enter the number of a Fibonacci Sequence:\n");
scanf("%d", &m);

if (m < 0)
        printf("Please enter a non-negative integer\n");
else if (m> MAX_SEQUENCE)
        printf("Please enter an integer less than 10\n");

int segment_id; /* the identifier for the shared memory segment */

int segment_size = sizeof(shared_data); /* the size (in bytes) of the shared memory segment */
segment_id = shmget(IPC_PRIVATE, segment_size, S_IRUSR | S_IWUSR); /** allocate  a shared memory segment */
shared_data *shared_memory = shmat(segment_id, NULL, 0); /** attach the shared memory segment */
printf("\nshared memory segment %d attached at address %p\n", segment_id, shared_memory);

shared_data->sequence_size = m;
pid_t pid;
pid = fork();
    if (pid == 0){
        printf("Child is producing the Fibonacci Sequence...\n");
        shared_data->fib_sequence[0] = a;
    shared_data->fib_sequence[1] = b;
        for (i=2;i<shared_data->sequence_size;i++){
        n=a+b;
        shared_data->fib_sequence[i] = n;
        a=b;
        b=n;
        }
        printf("\nChild ends\n"); 
    }
    else{
        printf("Parent is waiting for child to complete...\n");
        wait(NULL);
        printf("Parent ends\n");
    for(i=0;i<= shared_data->sequence_size;i++)
        printf("%ld ", shared_data->fib_sequence[i]);
    }

/**printf("%s \n", shared_memory);  now print out the string from shared memory */

/** now detach the shared memory segment */ 
if ( shmdt(shared_memory) == -1) {
    fprintf(stderr, "Unable to detach\n");
}

/** now remove the shared memory segment */
shmctl(segment_id, IPC_RMID, NULL); 

return 0;
}

该语句是“设计斐波那契程序的一种方法是在父进程和子进程之间建立一个共享内存段。这种技术允许子级将斐波那契序列的内容写入共享内存段，并在子级完成时让父级输出序列。因为内存是共享的，所以子进程所做的任何更改也会反映在父进程中。该程序将使用POSIX共享内存结构，如http://graphics.im.ntu.edu.tw/~robin/courses/os07/code/03proc/shm-posix.c所述。该程序首先需要为共享内存段创建数据结构。这最容易使用结构来完成。这个数据结构将包含两项：1。大小为MAX_SEQUENCE的固定大小数组，它将保存斐波那契值和2。子进程要生成的序列的大小，即sequence_size，其中sequence_size≤max_sequence。

这些项可以在结构中表示，如下所示：

# define MAX_SEQUENCE 10
typedef struct{
long fib_sequence[MAX_SEQUENCE];
int sequence_size;
} shared_data;

专家的心智仁慈的帮助。

Answer 1

第一个问题：

int a,b,m,n,i,j;

sequence.fib_sequence[0] = a;
sequence.fib_sequence[1] = b;

您从不初始化A和B，因此会得到垃圾（和未定义的行为）。初始化

a = 0;
b = 1;

更深层次的问题：您设置了共享内存段，但从未使用它。您使用全局

shared_data sequence;

shared_data *shared_memory = shmat(...);

# include <stdlib.h>
# include <stdio.h>
# include <sys/shm.h>
# include <sys/stat.h>
# include <sys/types.h>
# include <unistd.h>
# include <sys/wait.h>
# include <errno.h>

// So we could use other sizes without editing the source.
#ifndef MAX_SEQUENCE
# define MAX_SEQUENCE 10
#endif

// Check that MAX_SEQUENCE is large enough!
#if MAX_SEQUENCE < 2
#error MAX_SEQUENCE must be at least 2
#endif

typedef struct{
    long fib_sequence[MAX_SEQUENCE];
    int sequence_size;
} shared_data;

int main()
{
    int a, b, m, n, i;
    a = 0; b = 1;
    printf("Enter the number of a Fibonacci Sequence:\n");
    // Always check whether input conversion worked
    if (scanf("%d", &m) != 1) {
        printf("Invalid input, couldn't be converted.\n");
        return EXIT_FAILURE;
    }

    if (m <= 0) {
        printf("Please enter a positive integer\n");
        return EXIT_FAILURE;  // exit if input is invalid
    } else if (m > MAX_SEQUENCE) {
        printf("Please enter an integer less than %d\n", MAX_SEQUENCE);
        return EXIT_FAILURE;  // exit if input is invalid
    }

    /* the identifier for the shared memory segment */
    int segment_id;

    /* the size (in bytes) of the shared memory segment */
    size_t segment_size = sizeof(shared_data);

    /* allocate  a shared memory segment */
    segment_id = shmget(IPC_PRIVATE, segment_size, S_IRUSR | S_IWUSR);

    // Check result of shmget
    if (segment_id == -1) {
        perror("shmget failed");
        return EXIT_FAILURE;
    }

    /* attach the shared memory segment */
    shared_data *shared_memory = shmat(segment_id, NULL, 0);

    // Check whether attaching succeeded
    if ((void*)shared_memory == (void*)-1) {
        perror("shmat failed");
        goto destroy; // clean up
    }
    printf("\nshared memory segment %d attached at address %p\n", segment_id, (void*)shared_memory);

    shared_memory->sequence_size = m;
    pid_t pid;
    pid = fork();
    if (pid == 0){
        printf("Child is producing the Fibonacci Sequence...\n");
        shared_memory->fib_sequence[0] = a;
        shared_memory->fib_sequence[1] = b;
        for (i = 2; i < shared_memory->sequence_size; i++){
            n = a+b;
            shared_memory->fib_sequence[i] = n;
            a = b;
            b = n;
        }
        printf("\nChild ends\n"); 
    }
    else{
        printf("Parent is waiting for child to complete...\n");
        wait(NULL);
        printf("Parent ends\n");
        for(i = 0; i < shared_memory->sequence_size; i++) {
            printf("%ld ", shared_memory->fib_sequence[i]);
        }
        printf("\n");
    }

    /* now detach the shared memory segment */ 
    if (shmdt(shared_memory) == -1) {
        fprintf(stderr, "Unable to detach\n");
    }

    destroy:
    /* now remove the shared memory segment */
    shmctl(segment_id, IPC_RMID, NULL); 

    return 0;
}