🍱 🤘🏿 😮 fork () is evil; vfork () - good; afork () is better; clone ()

popen() ( , API) clone(2), issue vfork(2) posix_spawn() . , Linux clone(2). , , , - : , , .

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- , Unix, , fork(2) fork-exec , Windows , exec*() _spawn*(), .

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, 4.4BSD , . . 4.4BSD . : vfork(2)

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. vfork(2)

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_spawn()

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posix_spawn()

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exec()

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API, : ! fork(2)

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vfork()

fork()

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vfork()

: ( , , vfork()

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avfork()

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pthread_create()

: , .

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afork()

API popen()

I/O . - , , ( ) EOF, / EPIPE / SIGPIPE, popen()

.

forkx()/vforkx() Illumos , afork()

- :

pid_t afork(int (*start_routine)(void *), void *arg);
pid_t aforkx(int flags /* FORK_NOSIGCHLD / FORK_WAITPID */, int (*fn)(void *), void *arg);

, afork()

Linux: clone(<function>

, <stack>

, CLONE_VM | CLONE_SETTLS

, <argument>

). ( , SIGCHLD , , popen()

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- afork ()

( Illumos forkx()

) POSIX, pthread_create()

, vfork()

, afork()

. taskq, , , afork()

. afork()

, , PID, taskq pre-vfork ( !), , - :

int emulated_afork(int (*start_routine)(void *), void *arg, void (*cb)(pid_t) /*   NULL */);

pre-vfork, PID afork()

, pre-vfork

: pthread_cond_wait()

, , . ( vfork()

. , read()

write()

vfork()

) :

//  ,   vfork()       ,   vfork(),    . ,   Linux.
//      ,    avfork() . ,  Linux    clone(2).

static struct avfork_taskq_s { /*  */ ... } *avfork_taskq;
static void
avfork_taskq_init(void)
{
    // ,     
    ...
}

//  taskq ,  ,  
// taskq    
static void *
worker_start_routine(void *arg)
{
    struct worker_s *me = arg;
    struct job_s *job;
    

    //    pthread_cond_signal()    ,    .
    avfork_taskq_add_worker(avfork_taskq, me);

    do {
        if ((job = calloc(1, sizeof(*job))) == NULL ||
            pipe2(job->dispatch_pipe, O_CLOEXEC) == -1 ||
            pipe2(job->ready_pipe, O_CLOEXEC) == -1 ||
            (pid = vfork()) == -1) {
            avfork_taskq_remove(avfork_taskq, me, errno);  // !
            break;
        }
        if (pid != 0) {
            //     exit  exec
            if (job->errno)
                //      
                reap_child(pid);
            else
                //    ;  ,        .
                //            ,    .
                avfork_taskq_record_child(avfork_taskq, me, job, pid);
                

            if (avfork_taskq_too_big_p(avfork_taskq))
                break;  //   taskq
            continue;
        }
        

        //  
      
        //  ,     read(2), write(2), _exit(2)  start_routine   avfork(). avfork() start_routine()    ,    ,     ,      vfork().       C     -    : ,  , , RTLD  ..   , dup2(2), close(2), sigaction(2),   , exec(2)  _exit(2)     start_routine(),      posix_spawn(),   popen(),  system ()  ..

        //   ,        taskq.

        //  

        if (net_read(me->dispatch_pipe[0], &job->descr, sizeof(job->descr)) != sizeof(job->descr)) {
            job->errno = errno ? errno : EINVAL;
            _exit(1);
        }
        job->descr->pid = getpid();  //  pid,        
        if(net_write(me->ready_pipe[1], "", sizeof("")) != sizeof(""))  {
            job->errno = errno;
            _exit(1);
        }


        // 
        _exit(job->descr->start_routine(job->descr->arg));
    } while(!avfork_taskq->terminated); // ,    atexit()
    return NULL;
}
pid_t
avfork(int (*start_routine)(void *), void *arg)
{
    static pthread_once_t once = PTHREAD_ONCE_INIT;
    struct worker_s *worker;
    struct job_descr_s job;
    struct job_descr_s *jobp = &job;
    char c;

    // avfork_taskq_init()  ,   ,   .     N  ,   ,    ,  taskq.get_worker()   pthread_cond_wait(),     .
    pthread_once(&once, avfork_taskq_init);


    //  
    memset(&job, 0, sizeof(job));
    job.start_routine = start_routine;
    job.arg = arg;
    worker = avfork_taskq_get_worker(avfork_taskq); //  ,   ;    
    //    .   ,   ,  pre-vfork()        .    ,      vfork().         ,     .
    //
    //  taskq   ,        ,   ,     .
    // ,    ,   ,   ,    ( worker_start_routine()).
    if (net_write(worker->dispatch_pipe[1], &jobp, sizeof(jobp)) != sizeof(jobp) ||
        net_read(worker->ready_pipe[0], &c, sizeof(c)) != sizeof(c))
        job.errno = errno ? errno : EINVAL;
    // 
    (void) close(worker->dispatch_pipe[0]);
    (void) close(worker->dispatch_pipe[1]);
    (void) close(worker->ready_pipe[0]);
    (void) close(worker->ready_pipe[1]);


    if (job.errno)
        return -1;
    return job.pid; //   , PID   pid
}

, clone(2) - . . clone (2) POSIX, POSIX. , fork()

, , , , avfork()

! avfork()

. NPTL .

Linux - , pthread

Linux. Linux Solaris/SVR4, BSD libsocket STREAMS . API API .

clone()

- , /jail’, : Linux /jail’, clone(2)

, . clone(2)

, ... clone(2)

, .

Linux fork()

, vfork()

, avfork()

, thread_create()

container_create()

. , ( minder/init). , , /// , . clone(2)

, , .

, , «, - /jail’, », . /jail’, Linux /jail’. , . /jail’ , . - , , , clone(2) . , « » ( Linux : , C, , shell’, , - ). .

. . , fork()

, vfork()

, afork()

( ) clone()

( !). , 4.4BSD vfork()

( ). , , , , .

« ».

fork () is evil; vfork () - good; afork () is better; clone () - stupid

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