没有 pthreads 的 C 多线程 : "The program no longer exists" Seg fault

Question

这是一个我们必须在没有 pthreads 的情况下进行多线程的作业。每个线程中要执行的代码计算 0 和输入整数参数之间的数字总和。到目前为止，该程序仅在使用单个线程时运行良好，但在尝试创建多个线程时出现段错误。

我从几个来源获得了一些代码并对其进行了修改以获得以下内容:

#define _GNU_SOURCE
#include <malloc.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <signal.h>
#include <sched.h>
#include <stdio.h>
#include <stdlib.h>


//Source for threading outline: http://www.evanjones.ca/software/threading.html

// 64kB stack
#define FIBER_STACK 1024*64

struct sum_runner_struct {
    long long limit;
    long long answer;
};

// The child threads will execute this function
int threadFunction( void* argument )
{
    struct sum_runner_struct *arg_struct = (struct sum_runner_struct*) argument;
    long long sum = 0;
    long long i = 0;
    //Calculate the sum of numbers between 0 and input argument
    for (i; i <= arg_struct->limit; i++) {
        sum+=i;
    }

    arg_struct->answer = sum;
         printf( "child thread exiting\n" );
         return 0;
}

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

    if (argc < 2) {
        printf("Wrong number of args\n");
        exit(-1);
    }

    int num_args = argc - 1;

    struct sum_runner_struct args[num_args];


         void* stack;
     //Thread IDs
         pid_t pids[num_args];

         // Allocate the stack
         stack = malloc( FIBER_STACK );
         if ( stack == 0 )
         {
                 perror( "malloc: could not allocate stack" );
                 exit( 1 );
         }

         printf( "Creating child threads\n" );

    int i = 0;
    for (i; i < num_args; i++) {
        args[i].limit = atoll(argv[i + 1]);

            // Call the clone system call to create the child threads
             pids[i] = clone( &threadFunction, (char*) stack + FIBER_STACK,
                 SIGCHLD | CLONE_FS | CLONE_FILES | CLONE_SIGHAND | CLONE_VM, &args[i] );
             if ( pids[i] == -1 )
                 {
                        perror( "clone" );
                        exit( 2 );
             }
    }

    int j = 0;
    for (j; j < num_args; j++) {
            // Wait for the child threads to exit
            pids[j] = waitpid( pids[j], 0, 0 );
        //Prints the answers that were computed in the child threads
        printf("Sum is %lld\n", args[j].answer);
            if ( pids[j] == -1 )
                {
                        perror( "waitpid" );
                        exit( 3 );
                 }
            }
         // Free the stack
         free( stack );

         printf( "Child threads returned and stack freed.\n" );

         return 0;
}

使用gdb调试，程序执行到第70行，此时线程被创建:

pids[i] = clone( &threadFunction, (char*) stack + FIBER_STACK,
                 SIGCHLD | CLONE_FS | CLONE_FILES | CLONE_SIGHAND | CLONE_VM, &args[i] );

然后当我越过它时我得到这个:

70               pids[i] = clone( &threadFunction, (char*) stack + FIBER_STACK,
(gdb) s
Detaching after fork from child process 29143.
child thread exiting
Detaching after fork from child process 29144.

Program terminated with signal SIGSEGV, Segmentation fault.
The program no longer exists.

同样，这只会在尝试创建多个线程时发生。该程序仅使用一个线程即可按预期工作。

如有任何帮助，我们将不胜感激!

Answer 1

您正在将相同的堆栈传递给所有线程。因此，线程将相互踩踏。以及为什么它适用于一个线程。