cosmopolitan/libc/proc/fork.c

/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8                               :vi │
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
│                                                                              │
│ Permission to use, copy, modify, and/or distribute this software for         │
│ any purpose with or without fee is hereby granted, provided that the         │
│ above copyright notice and this permission notice appear in all copies.      │
│                                                                              │
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
│ PERFORMANCE OF THIS SOFTWARE.                                                │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/calls/calls.h"
#include "libc/calls/sig.internal.h"
#include "libc/calls/state.internal.h"
#include "libc/calls/struct/sigset.internal.h"
#include "libc/calls/struct/timespec.h"
#include "libc/calls/syscall-nt.internal.h"
#include "libc/calls/syscall-sysv.internal.h"
#include "libc/dce.h"
#include "libc/intrin/atomic.h"
#include "libc/intrin/cxaatexit.h"
#include "libc/intrin/dll.h"
#include "libc/intrin/maps.h"
#include "libc/intrin/stack.h"
#include "libc/intrin/strace.h"
#include "libc/intrin/weaken.h"
#include "libc/nt/files.h"
#include "libc/nt/process.h"
#include "libc/nt/runtime.h"
#include "libc/nt/thread.h"
#include "libc/nt/thunk/msabi.h"
#include "libc/proc/proc.internal.h"
#include "libc/runtime/internal.h"
#include "libc/runtime/syslib.internal.h"
#include "libc/stdio/internal.h"
#include "libc/str/str.h"
#include "libc/thread/itimer.h"
#include "libc/thread/posixthread.internal.h"
#include "libc/thread/thread.h"
#include "third_party/dlmalloc/dlmalloc.h"
#include "third_party/gdtoa/lock.h"
#include "third_party/tz/lock.h"

__msabi extern typeof(GetCurrentProcessId) *const __imp_GetCurrentProcessId;

extern pthread_mutex_t __rand64_lock_obj;
extern pthread_mutex_t __pthread_lock_obj;
extern pthread_mutex_t __cxa_lock_obj;
extern pthread_mutex_t __sig_worker_lock;

void nsync_mu_semaphore_sem_fork_child(void);

// first and last and always
// it is the lord of all locks
// subordinate to no other lock
static pthread_mutex_t supreme_lock = PTHREAD_MUTEX_INITIALIZER;

static void fork_prepare_stdio(void) {
  struct Dll *e;
  // we acquire the following locks, in order
  //
  //   1. FILE objects created by the user
  //   2. stdin, stdout, and stderr
  //   3. __stdio.lock
  //
StartOver:
  __stdio_lock();
  for (e = dll_last(__stdio.files); e; e = dll_prev(__stdio.files, e)) {
    FILE *f = FILE_CONTAINER(e);
    if (f->forking)
      continue;
    f->forking = 1;
    __stdio_ref(f);
    __stdio_unlock();
    pthread_mutex_lock(&f->lock);
    __stdio_unref(f);
    goto StartOver;
  }
}

static void fork_parent_stdio(void) {
  struct Dll *e;
  for (e = dll_first(__stdio.files); e; e = dll_next(__stdio.files, e)) {
    FILE_CONTAINER(e)->forking = 0;
    pthread_mutex_unlock(&FILE_CONTAINER(e)->lock);
  }
  __stdio_unlock();
}

static void fork_child_stdio(void) {
  struct Dll *e;
  for (e = dll_first(__stdio.files); e; e = dll_next(__stdio.files, e)) {
    pthread_mutex_wipe_np(&FILE_CONTAINER(e)->lock);
    FILE_CONTAINER(e)->forking = 0;
  }
  pthread_mutex_wipe_np(&__stdio.lock);
}

static void fork_prepare(void) {
  pthread_mutex_lock(&supreme_lock);
  if (_weaken(_pthread_onfork_prepare))
    _weaken(_pthread_onfork_prepare)();
  fork_prepare_stdio();
  __localtime_lock();
  __cxa_lock();
  __gdtoa_lock1();
  __gdtoa_lock();
  _pthread_lock();
  dlmalloc_pre_fork();
  __fds_lock();
  pthread_mutex_lock(&__rand64_lock_obj);
  if (_weaken(cosmo_stack_lock))
    _weaken(cosmo_stack_lock)();
  __maps_lock();
  LOCKTRACE("READY TO LOCK AND ROLL");
}

static void fork_parent(void) {
  __maps_unlock();
  if (_weaken(cosmo_stack_unlock))
    _weaken(cosmo_stack_unlock)();
  pthread_mutex_unlock(&__rand64_lock_obj);
  __fds_unlock();
  dlmalloc_post_fork_parent();
  _pthread_unlock();
  __gdtoa_unlock();
  __gdtoa_unlock1();
  __cxa_unlock();
  __localtime_unlock();
  fork_parent_stdio();
  if (_weaken(_pthread_onfork_parent))
    _weaken(_pthread_onfork_parent)();
  pthread_mutex_unlock(&supreme_lock);
}

static void fork_child(void) {
  nsync_mu_semaphore_sem_fork_child();
  if (_weaken(cosmo_stack_wipe))
    _weaken(cosmo_stack_wipe)();
  pthread_mutex_wipe_np(&__rand64_lock_obj);
  pthread_mutex_wipe_np(&__fds_lock_obj);
  dlmalloc_post_fork_child();
  pthread_mutex_wipe_np(&__gdtoa_lock_obj);
  pthread_mutex_wipe_np(&__gdtoa_lock1_obj);
  fork_child_stdio();
  pthread_mutex_wipe_np(&__pthread_lock_obj);
  pthread_mutex_wipe_np(&__cxa_lock_obj);
  pthread_mutex_wipe_np(&__localtime_lock_obj);
  if (IsWindows()) {
    // we don't bother locking the proc/itimer/sig locks above since
    // their state is reset in the forked child. nothing to protect.
    __proc_wipe_and_reset();
    __itimer_wipe_and_reset();
    pthread_mutex_wipe_np(&__sig_worker_lock);
    if (_weaken(__sig_init))
      _weaken(__sig_init)();
  }
  if (_weaken(_pthread_onfork_child))
    _weaken(_pthread_onfork_child)();
  pthread_mutex_wipe_np(&supreme_lock);
}

int _fork(uint32_t dwCreationFlags) {
  long micros;
  struct Dll *e;
  struct timespec started;
  int ax, dx, tid, parent;
  parent = __pid;
  started = timespec_mono();
  BLOCK_SIGNALS;
  fork_prepare();
  if (!IsWindows()) {
    ax = sys_fork();
  } else {
    ax = sys_fork_nt(dwCreationFlags);
  }
  micros = timespec_tomicros(timespec_sub(timespec_mono(), started));
  if (!ax) {

    // get new process id
    if (!IsWindows()) {
      dx = sys_getpid().ax;
    } else {
      dx = __imp_GetCurrentProcessId();
    }
    __pid = dx;

    // get new thread id
    struct CosmoTib *tib = __get_tls();
    struct PosixThread *pt = (struct PosixThread *)tib->tib_pthread;
    tid = IsLinux() || IsXnuSilicon() ? dx : sys_gettid();
    atomic_store_explicit(&tib->tib_tid, tid, memory_order_relaxed);
    atomic_store_explicit(&pt->ptid, tid, memory_order_relaxed);

    // tracing and kisdangerous need this lock wiped a little earlier
    atomic_store_explicit(&__maps.lock.word, 0, memory_order_relaxed);

    /*
     * it's now safe to call normal functions again
     */

    // turn other threads into zombies
    // we can't free() them since we're monopolizing all locks
    // we assume the operating system already reclaimed system handles
    dll_remove(&_pthread_list, &pt->list);
    for (e = dll_first(_pthread_list); e; e = dll_next(_pthread_list, e)) {
      atomic_store_explicit(&POSIXTHREAD_CONTAINER(e)->pt_status,
                            kPosixThreadZombie, memory_order_relaxed);
      atomic_store_explicit(&POSIXTHREAD_CONTAINER(e)->tib->tib_syshand, 0,
                            memory_order_relaxed);
    }
    dll_make_first(&_pthread_list, &pt->list);
    atomic_store_explicit(&_pthread_count, 1, memory_order_relaxed);

    // get new system thread handle
    intptr_t syshand = 0;
    if (IsXnuSilicon()) {
      syshand = __syslib->__pthread_self();
    } else if (IsWindows()) {
      DuplicateHandle(GetCurrentProcess(), GetCurrentThread(),
                      GetCurrentProcess(), &syshand, 0, false,
                      kNtDuplicateSameAccess);
    }
    atomic_store_explicit(&tib->tib_syshand, syshand, memory_order_relaxed);

    // we can't be canceled if the canceler no longer exists
    atomic_store_explicit(&pt->pt_canceled, false, memory_order_relaxed);

    // forget locks
    memset(tib->tib_locks, 0, sizeof(tib->tib_locks));

    // run user fork callbacks
    fork_child();
    STRACE("fork() → 0 (child of %d; took %ld us)", parent, micros);
  } else {
    // this is the parent process
    fork_parent();
    STRACE("fork() → %d% m (took %ld us)", ax, micros);
  }
  ALLOW_SIGNALS;
  return ax;
}

/**
 * Creates new process.
 *
 * @return 0 to child, child pid to parent, or -1 w/ errno
 * @raise EAGAIN if `RLIMIT_NPROC` was exceeded or system lacked resources
 * @raise ENOMEM if we require more vespene gas
 * @asyncsignalsafe
 */
int fork(void) {
  return _fork(0);
}