Question

我有这个项目，我从命令行接收输入，如“54 342 12”，它假设为每个输入创建一个线程，并让线程返回一个整数数组，然后主线程支持打印出不同的主要因素。但我收到奇怪的输出，如一堆零。我不知道为什么和任何帮助将不胜感激。

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


typedef struct _thread_data_t {
        int tid;
        } thread_data_t;

void *runner(void *param);

int main(int argc, char *argv[]) {

        pthread_t thr[argc];
        pthread_attr_t attr;
        int i, rc;
        //int *primeFactor;
        //primeFactor = (int *)malloc(sizeof(int)*argc);
        //thread_data_t thr_data[argc];
        printf("Prime Numbers: ");

        //Get the default attributes
        pthread_attr_init(&attr);
        //creat the thread
        for(i = 1; i < argc; ++i){
        //thr_data[i].tid = i;
        if ((rc = pthread_create(&thr[i],&attr,runner,argv[i]))){
                fprintf(stderr, "error: pthread_create, rc: %d\n", rc);
                return EXIT_FAILURE;
                }
        }

        //Wait for the thread to exit
        for(i = 1; i < argc; ++i){
        void *returnValue;
        int r = 0;
        int x = (sizeof(returnValue) / sizeof(returnValue[0])) - 1;
        pthread_join(thr[i], &returnValue);
                for(r = 0; r < x; r++){
                //int c = (int *)returnValue[r];
                printf("%d ",  ((int *)returnValue)[r]);
                }
        }
        printf("\nComplete\n");

}

//The Thread will begin control in this function
void *runner(void *param) {
        int *primeFactors;
        int num = atoi(param);
        primeFactors = (int *)malloc(sizeof(int)*num);
        int i, j, isPrime;
        int k = 0;
        for(i=2; i<=num; i++)
        {
                if(num%i==0)
                {
                        isPrime=1;
                        for(j=2; j<=i/2; j++)
                        {
                                if(i%j==0)
                                {
                                        isPrime = 0;
                                        break;
                                }
                        }

                        if(isPrime==1)
                        {
                                primeFactors[k] = i;
                                k++;
                        }
                }
        }


        //Exit the thread
//      pthread_exit(0);

//      pthread_exit((void *)primeFactors);
        pthread_exit(primeFactors);
}

Answer 1

这一行是个问题：

int x = (sizeof(returnValue) / sizeof(returnValue[0])) - 1;

sizeof array / sizeof array[0]仅适用于纯数组，而不适用于指针。请注意，returnValue是指针，因此sizeof(returnValue)可以不返回线程创建的整数序列的字节大小，它给出指针需要存储在内存中的字节数。上 x86_64架构很可能是8，所以x在大多数情况下都是如此大于主要因子的实际数量，你将访问指针超出界限，这就是你看到垃圾值的原因。

因为您要返回指向malloc ed位置的指针，所以需要返回长度也是如此。最好的方法是为它创建一个结构返回值并将信息存储在那里。

创建结构

struct thread_result
{
    int *factors;
    size_t len;
};

并返回一个指向此结构的指针，其中包含以下信息：

void *runner(void *param) {
        int *primeFactors;
        int num = atoi(param);
        if(num == 0)
            pthread_exit(NULL);

        struct thread_result *res = calloc(1, sizeof *res);

        res->factors = NULL;
        res->len = 0;

        int *tmp;

        if(res == NULL)
            pthread_exit(NULL);

        int i, j, isPrime;
        int k = 0;
        for(i=2; i<=num; i++)
        {
            if(num%i==0)
            {
                isPrime=1;
                for(j=2; j<=i/2; j++)
                {
                    if(i%j==0)
                    {
                            isPrime = 0;
                            break;
                    }
                }

                if(isPrime==1)
                {
                    tmp = realloc(res->factors, (k+1) * sizeof *res->factors);
                    if(tmp == NULL)
                    {
                        free(res->factors);
                        free(res);
                        pthread_exit(NULL);
                    }
                    res->factors = tmp;

                    res->factors[k++] = i;
                    res->len = k;
                }
            }
        }


        pthread_exit(res);
}

现在你可以得到这样的值：

for(i = 1; i < argc; ++i){
    void *data;
    pthread_join(thr[i], &data);

    if(data == NULL)
        continue; // error in thread

    struct thread_result *res = data;

    for(size_t r = 0; r < res->len; r++){
        printf("%d ", res->factors[r]);
    }

    free(res->factors);
    free(res);
}

并且不要忘记使用

销毁线程属性

pthread_attr_destroy(&attr);

离开main之前。但是你没有为线程设置任何属性，所以你可以使用：

创建线程

pthread_create(&thr[i], NULL, runner, argv[i]);

同样don't cast malloc，您必须检查返回值 malloc。

修改

OP在评论中写道

我认为我正确地更新了所有代码以匹配您所说的内容，但现在我收到了错误＆＃34; Segmentation dump（core dumped）＆＃34;知道为什么会这样吗？

实际上没有，但你一定错过了某个地方，因为当我编译并运行此代码：

#include <pthread.h> #include <stdio.h> #include <stdlib.h> typedef struct _thread_data_t { int tid; } thread_data_t; void *runner(void *param); struct thread_result { int *factors; size_t len; }; int main(int argc, char *argv[]) { pthread_t thr[argc]; int i, rc; printf("Prime Numbers:\n"); for(i = 1; i < argc; ++i){ if ((rc = pthread_create(&thr[i],NULL,runner,argv[i]))){ fprintf(stderr, "error: pthread_create, rc: %d\n", rc); return EXIT_FAILURE; } } for(i = 1; i < argc; ++i){ void *data; pthread_join(thr[i], &data); if(data == NULL) continue; // error in thread struct thread_result *res = data; for(size_t r = 0; r < res->len; r++){ printf("%d ", res->factors[r]); } free(res->factors); free(res); puts(""); } } void *runner(void *param) { int num = atoi(param); if(num == 0) pthread_exit(NULL); struct thread_result *res = calloc(1, sizeof *res); res->factors = NULL; res->len = 0; int *tmp; if(res == NULL) pthread_exit(NULL); int i, j, isPrime; int k = 0; for(i=2; i<=num; i++) { if(num%i==0) { isPrime=1; for(j=2; j<=i/2; j++) { if(i%j==0) { isPrime = 0; break; } } if(isPrime==1) { tmp = realloc(res->factors, (k+1) * sizeof *res->factors); if(tmp == NULL) { free(res->factors); free(res); pthread_exit(NULL); } res->factors = tmp; res->factors[k++] = i; res->len = k; } } } pthread_exit(res); }

我得到了这个输出：

$ valgrind ./a 54 342 12 ==17697== Memcheck, a memory error detector ==17697== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al. ==17697== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info ==17697== Command: ./a 54 342 12 ==17697== Prime Numbers: 2 3 2 3 19 2 3 ==17697== ==17697== HEAP SUMMARY: ==17697== in use at exit: 0 bytes in 0 blocks ==17697== total heap usage: 19 allocs, 19 frees, 3,640 bytes allocated ==17697== ==17697== All heap blocks were freed -- no leaks are possible ==17697== ==17697== For counts of detected and suppressed errors, rerun with: -v ==17697== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

告诉我一切正常，并且所有内存都已被释放好。

因此，当您复制＆amp ;;时，您一定会犯错粘贴我的代码答案。

Pthread Posix素因子化得到奇怪的结果？

1 个答案: