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Question

我在实施多线程程序时遇到问题。该程序似乎适用于单个线程（当我将THREADS设置为1时）但是对于NTHREADS＆gt; 1，我收到以下错误： Segmentation fault (core dumped)

或

double free or corruption (!prev)

或

free(): invalid size: 0xb6b00a10 *** 0Aborted (core dumped)

你可以看到错误变化很大，我感到很困惑。

我执行的程序如下：

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>
#include <pthread.h>
#define NTHREADS 5
typedef struct data_t
{
    int num;
    FILE *fp;
    pthread_mutex_t mutex;
    int thread_id;
}data_t;

void writefp(int num1, FILE *fp){
    if(fp!=NULL){
        int i;
        int nume = 1;
        int long_var=log10(nume);
        for(i=long_var;i>=0;i--){
            nume=(num1 / (int) round(pow(10, i)) % 10);
            char d=nume+'0';
            fwrite(&d, 1, 1, fp);
            printf("%c", d);
        }
    }
    fclose(fp);
}

void *thread_writefp(void* args)
{
    data_t *data = (data_t *)args;
    printf(" Thread id %d\n", data->thread_id);

    pthread_mutex_lock(&(data->mutex));
    writefp(data->num, data->fp);
    pthread_mutex_unlock(&(data->mutex));
    pthread_exit(NULL);
}
int randomf(){
    int num,i;
    for(i = 0; i<2; i++) {
        num = rand()%100000+1;
    }
    return num;
}

int prime(int num1){
    int is_prime=1;
    int i = 2;
    printf("Number: ");
    while( i<=num1/2 && is_prime==1 ) {
        printf("%i ", i);
        if(i%30==0){
            printf("\n");
        }
        if( num1 % i == 0 ) {
                is_prime = 0;
        }
        i++;
    }
    printf("\n");
    if(is_prime){
            printf("%i is number prime\n", num1);
    }else{
             printf("NO is prime %i\n",num1);
    }
    return 0;
}


int main(void){
    int i;
    //int num1=randomf();
    srand(time(NULL));
    FILE *fp = fopen("fich.txt", "w+b");

    data_t data;
    pthread_t consumers_thread[NTHREADS];
    data.mutex = (pthread_mutex_t) PTHREAD_MUTEX_INITIALIZER;
    data.fp = fp;

    //writefp( num1, fp);
    for(i = 0; i < NTHREADS; i++)
    {
        data.num = randomf();
        data.thread_id = i;
        printf("Number prime is %i\n", prime(data.num));
        if(pthread_create(&consumers_thread[i], NULL, 
                    thread_writefp, (void*) &data) != 0)
        {
            fprintf(stderr, "%s\n", "Error creating thread!");
            return EXIT_FAILURE;
        }
    }
    // wait for all consumers thread to finish
    for(i = 0; i < NTHREADS; ++i)
    {
        pthread_join(consumers_thread[i], NULL);
    }
    return EXIT_SUCCESS;
}

我按如下方式编译程序：

$gcc -pthread -Wall -o consummer consummer.c -lm

以下是我连续gdb树连续运行时得到的例外树错误，而不更改代码：

1

Thread 2 "consummer" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0xb7cc1b40 (LWP 18122)]
tcache_thread_freeres () at malloc.c:3003
3003    malloc.c: No such file or directory.
(gdb) bt
#0  tcache_thread_freeres () at malloc.c:3003
#1  0xb7e258c2 in __libc_thread_freeres () at thread-freeres.c:29
#2  0xb7ea03ad in start_thread (arg=0xb7cc1b40) at pthread_create.c:478
#3  0xb7dbb0a6 in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:108
(gdb)

2

Thread 3 "consummer" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0xb72ffb40 (LWP 18131)]
0xb7d2af2b in __GI__IO_fwrite (buf=0xb72ff30f, size=1, count=1, fp=0x404160) at iofwrite.c:37
37  iofwrite.c: No such file or directory.
(gdb) run

3

Thread 3 "consummer" received signal SIGABRT, Aborted.
[Switching to Thread 0xb74c0b40 (LWP 18143)]
0xb7fd7cf9 in __kernel_vsyscall ()
(gdb) bt
#0  0xb7fd7cf9 in __kernel_vsyscall ()
#1  0xb7cf17e2 in __libc_signal_restore_set (set=0xb74bfe9c) at ../sysdeps/unix/sysv/linux/nptl-signals.h:80
#2  __GI_raise (sig=6) at ../sysdeps/unix/sysv/linux/raise.c:48
#3  0xb7cf2f51 in __GI_abort () at abort.c:90
#4  0xb7d340cc in __libc_message (action=(do_abort | do_backtrace), fmt=<optimized out>) at ../sysdeps/posix/libc_fatal.c:181
#5  0xb7d3af5d in malloc_printerr (action=<optimized out>, str=0xb7e418d8 "double free or corruption (!prev)", ptr=<optimized out>, 
ar_ptr=0xb7e967a0 <main_arena>) at malloc.c:5425
#6  0xb7d3bb3b in _int_free (av=0xb7e967a0 <main_arena>, p=<optimized out>, have_lock=have_lock@entry=0) at malloc.c:4174
#7  0xb7d3fcb0 in __GI___libc_free (mem=0x404160) at malloc.c:3144
#8  0xb7e2587d in tcache_thread_freeres () at malloc.c:3004
#9  0xb7e258c2 in __libc_thread_freeres () at thread-freeres.c:29
#10 0xb7ea03ad in start_thread (arg=0xb74c0b40) at pthread_create.c:478
#11 0xb7dbb0a6 in clone () at ../sysdeps/unix/sysv/linux/i386/clone.S:108
(gdb)

我希望/帮助你知道我做错了什么。提前致谢。

Answer 1

每this answer（但请参见编辑2 ），多个线程无法安全地访问相同的FILE *fp。正如@IlyaBursov指出的那样，您只有一个data_t data在所有主题中共享 - 因此，只有一个FILE * data.fp。

感谢your comment注意到您已将fopen移动到线程函数中。这样每个线程独立地打开和关闭文件，因此线程之间没有FILE *共享。

这似乎与实现有关 - 我无法使用gcc 6.4.0在Cygwin x64上重现该问题。我怀疑互斥体的效果也可能因实现而异。它也可能依赖于编译器选项 - 请参阅this example。

编辑正如@MichaelDorgan指出的那样，在其他线程正在使用的fclose上调用FILE *也是一个坏主意。

编辑2 正如@JohnBollinger指出的那样，individual stream operations are thread-safe这些天。这表明在另一个线程试图访问该文件之前fclose可能是问题所在。但是，我想知道OP的stdio实现是否在某种程度上不符合要求。我认为compliant fwrite只会在访问已关闭文件时返回错误，而不是崩溃。 请参阅下面的进一步评论。

双重免费或腐败（！prev）pthread

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1 个答案: