作为线程而不是进程运行外部程序

Question

I want to be able to run an external program as a pthread rather than as a separate process in C. How would I, for example, change the following program to use threads?

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

// ...other code

int main () {
    char* command[] = {"/bin/ls", NULL};
    pid_t pid = fork();

    if (pid == 0) {
        execv(command[0], command);
    } else {
        wait(NULL);
    }
    return 0;
}

Answer 1

This question doesn't make a lot of sense, as the major difference between a process and a thread is that threads share a single memory space, and an external program cannot do that. You might want to load a dynamic library or have two processes map a shared memory object, if you want them to share memory.

A way to run an external program from a child thread without replacing the process, though, is with popen() .

Answer 2

For your specific case, where you want to run shell commands, system() function call can be used in threads, eliminating need to create child process.

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

#define MAX_COUNT 10 // Change MAX_COUNT as per maximum number of commands possible

void ThreadFunc(char *command)
{
    int ret = 0;

    if (NULL == command)
    {
        printf("ERROR::Input pointer argument is NULL\n");
        return;
    }
    if ('\0' == command[0])
    {
        printf("ERROR::Input command string is EMPTY\n");
        return;
    }

    ret = system(command);
    if (0 != ret)
    {
        printf("ERROR::system(%s) failed. errno=%d\n", command, errno);
    }
    else
    {
        printf("SUCCESS::system(%s) succeeded\n", command);
    }
}

int main () 
{
    char* command[] = {"/bin/ls", NULL};
    int i = 0;
    int count = 0;
    int ret = 0;
    pthread_t threadId[MAX_COUNT]; // Change MAX_COUNT as per maximum number of commands possible

    while (NULL != command[i])
    {
        ret = pthread_create(&threadId[i], NULL, (void *(*)(void *))ThreadFunc, (void *)command[i]);
        if (0 != ret)
        {
            printf("ERROR::pthread_create() failed for command %s. errno = %d\n", command[i], errno);
        }
        else
        {
            printf("SUCCESS::pthread_create() succeeded for command %s\n", command[i]);
            count++; // update i
        }
        i++;
    }

    // pthread_join to wait till all thread are finished
    for (i = 0; i < count; i++)
    {
        pthread_join(threadId[i], NULL);
    }

    return 0;
}