[uclibc-ng.git] / libpthread / nptl / sysdeps / unix / sysv / linux / fork.c

/* Copyright (C) 2002, 2003, 2007, 2008 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <[email protected]>, 2002.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, write to the Free
   Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
   02111-1307 USA.  */

#include <assert.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sysdep.h>
#include <tls.h>
#include "fork.h"
#include <hp-timing.h>
#include <ldsodefs.h>
#include <atomic.h>
#include <errno.h>

unsigned long int *__fork_generation_pointer;


/* The single linked list of all currently registered for handlers.  */
struct fork_handler *__fork_handlers;


static void
fresetlockfiles (void)
{
  FILE *fp;
#ifdef __USE_STDIO_FUTEXES__
  for (fp = _stdio_openlist; fp != NULL; fp = fp->__nextopen)
    STDIO_INIT_MUTEX(fp->__lock);
#else
  pthread_mutexattr_t attr;

  pthread_mutexattr_init(&attr);
  pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE_NP);

  for (fp = _stdio_openlist; fp != NULL; fp = fp->__nextopen)
    pthread_mutex_init(&fp->__lock, &attr);

  pthread_mutexattr_destroy(&attr);
#endif
}


pid_t
__libc_fork (void)
{
  pid_t pid;
  struct used_handler
  {
    struct fork_handler *handler;
    struct used_handler *next;
  } *allp = NULL;

  /* Run all the registered preparation handlers.  In reverse order.
     While doing this we build up a list of all the entries.  */
  struct fork_handler *runp;
  while ((runp = __fork_handlers) != NULL)
    {
      /* Make sure we read from the current RUNP pointer.  */
      atomic_full_barrier ();

      unsigned int oldval = runp->refcntr;

      if (oldval == 0)
	/* This means some other thread removed the list just after
	   the pointer has been loaded.  Try again.  Either the list
	   is empty or we can retry it.  */
	continue;

      /* Bump the reference counter.  */
      if (atomic_compare_and_exchange_bool_acq (&__fork_handlers->refcntr,
						oldval + 1, oldval))
	/* The value changed, try again.  */
	continue;

      /* We bumped the reference counter for the first entry in the
	 list.  That means that none of the following entries will
	 just go away.  The unloading code works in the order of the
	 list.

         While executing the registered handlers we are building a
         list of all the entries so that we can go backward later on.  */
      while (1)
	{
	  /* Execute the handler if there is one.  */
	  if (runp->prepare_handler != NULL)
	    runp->prepare_handler ();

	  /* Create a new element for the list.  */
	  struct used_handler *newp
	    = (struct used_handler *) alloca (sizeof (*newp));
	  newp->handler = runp;
	  newp->next = allp;
	  allp = newp;

	  /* Advance to the next handler.  */
	  runp = runp->next;
	  if (runp == NULL)
	    break;

	  /* Bump the reference counter for the next entry.  */
	  atomic_increment (&runp->refcntr);
	}

      /* We are done.  */
      break;
    }

  __UCLIBC_IO_MUTEX_LOCK_CANCEL_UNSAFE(_stdio_openlist_add_lock);

#ifndef NDEBUG
  pid_t ppid = THREAD_GETMEM (THREAD_SELF, tid);
#endif

  /* We need to prevent the getpid() code to update the PID field so
     that, if a signal arrives in the child very early and the signal
     handler uses getpid(), the value returned is correct.  */
  pid_t parentpid = THREAD_GETMEM (THREAD_SELF, pid);
  THREAD_SETMEM (THREAD_SELF, pid, -parentpid);

#ifdef ARCH_FORK
  pid = ARCH_FORK ();
#else
# error "ARCH_FORK must be defined so that the CLONE_SETTID flag is used"
  pid = INLINE_SYSCALL (fork, 0);
#endif


  if (pid == 0)
    {
      struct pthread *self = THREAD_SELF;

      assert (THREAD_GETMEM (self, tid) != ppid);

      if (__fork_generation_pointer != NULL)
	*__fork_generation_pointer += 4;

      /* Adjust the PID field for the new process.  */
      THREAD_SETMEM (self, pid, THREAD_GETMEM (self, tid));

#if HP_TIMING_AVAIL
      /* The CPU clock of the thread and process have to be set to zero.  */
      hp_timing_t now;
      HP_TIMING_NOW (now);
      THREAD_SETMEM (self, cpuclock_offset, now);
      GL(dl_cpuclock_offset) = now;
#endif

      /* Reset the file list.  These are recursive mutexes.  */
      fresetlockfiles ();

      /* Reset locks in the I/O code.  */
      STDIO_INIT_MUTEX(_stdio_openlist_add_lock);

      /* XXX reset any locks in dynamic loader */

      /* Run the handlers registered for the child.  */
      while (allp != NULL)
	{
	  if (allp->handler->child_handler != NULL)
	    allp->handler->child_handler ();

	  /* Note that we do not have to wake any possible waiter.
 	     This is the only thread in the new process.  The count
 	     may have been bumped up by other threads doing a fork.
 	     We reset it to 1, to avoid waiting for non-existing
 	     thread(s) to release the count.  */
	  allp->handler->refcntr = 1;

	  /* XXX We could at this point look through the object pool
	     and mark all objects not on the __fork_handlers list as
	     unused.  This is necessary in case the fork() happened
	     while another thread called dlclose() and that call had
	     to create a new list.  */

	  allp = allp->next;
	}

      /* Initialize the fork lock.  */
      __fork_lock = LLL_LOCK_INITIALIZER;
    }
  else
    {
      assert (THREAD_GETMEM (THREAD_SELF, tid) == ppid);

      /* Restore the PID value.  */
      THREAD_SETMEM (THREAD_SELF, pid, parentpid);

      /* We execute this even if the 'fork' call failed.  */
      __UCLIBC_IO_MUTEX_UNLOCK_CANCEL_UNSAFE(_stdio_openlist_add_lock);

      /* Run the handlers registered for the parent.  */
      while (allp != NULL)
	{
	  if (allp->handler->parent_handler != NULL)
	    allp->handler->parent_handler ();

	  if (atomic_decrement_and_test (&allp->handler->refcntr)
	      && allp->handler->need_signal)
	    lll_futex_wake (allp->handler->refcntr, 1, LLL_PRIVATE);

	  allp = allp->next;
	}
    }

  return pid;
}
weak_alias(__libc_fork,__fork)
libc_hidden_proto(fork)
weak_alias(__libc_fork,fork)
libc_hidden_weak(fork)
Commit	Line	Data
a032a658	1	/* Copyright (C) 2002, 2003, 2007, 2008 Free Software Foundation, Inc.
c68d0fa2 AF	2	This file is part of the GNU C Library.
	3	Contributed by Ulrich Drepper <[email protected]>, 2002.
	4
	5	The GNU C Library is free software; you can redistribute it and/or
	6	modify it under the terms of the GNU Lesser General Public
	7	License as published by the Free Software Foundation; either
	8	version 2.1 of the License, or (at your option) any later version.
	9
	10	The GNU C Library is distributed in the hope that it will be useful,
	11	but WITHOUT ANY WARRANTY; without even the implied warranty of
	12	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
	13	Lesser General Public License for more details.
	14
	15	You should have received a copy of the GNU Lesser General Public
	16	License along with the GNU C Library; if not, write to the Free
	17	Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
	18	02111-1307 USA. */
	19
	20	#include <assert.h>
	21	#include <stdlib.h>
	22	#include <stdio.h>
	23	#include <unistd.h>
	24	#include <sys/types.h>
	25	#include <sysdep.h>
	26	#include <tls.h>
	27	#include "fork.h"
	28	#include <hp-timing.h>
	29	#include <ldsodefs.h>
	30	#include <atomic.h>
	31	#include <errno.h>
	32
	33	unsigned long int *__fork_generation_pointer;
	34
	35
	36
	37	/* The single linked list of all currently registered for handlers. */
	38	struct fork_handler *__fork_handlers;
	39
	40
	41	static void
	42	fresetlockfiles (void)
	43	{
	44	FILE *fp;
	45	#ifdef __USE_STDIO_FUTEXES__
	46	for (fp = _stdio_openlist; fp != NULL; fp = fp->__nextopen)
	47	STDIO_INIT_MUTEX(fp->__lock);
	48	#else
	49	pthread_mutexattr_t attr;
	50
	51	pthread_mutexattr_init(&attr);
	52	pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE_NP);
	53
	54	for (fp = _stdio_openlist; fp != NULL; fp = fp->__nextopen)
	55	pthread_mutex_init(&fp->__lock, &attr);
	56
	57	pthread_mutexattr_destroy(&attr);
	58	#endif
	59	}
	60
a032a658 AF	61
	62	pid_t
	63	__libc_fork (void)
c68d0fa2 AF	64	{
	65	pid_t pid;
	66	struct used_handler
	67	{
	68	struct fork_handler *handler;
	69	struct used_handler *next;
	70	} *allp = NULL;
	71
	72	/* Run all the registered preparation handlers. In reverse order.
	73	While doing this we build up a list of all the entries. */
	74	struct fork_handler *runp;
	75	while ((runp = __fork_handlers) != NULL)
	76	{
a032a658 AF	77	/* Make sure we read from the current RUNP pointer. */
	78	atomic_full_barrier ();
	79
c68d0fa2 AF	80	unsigned int oldval = runp->refcntr;
	81
	82	if (oldval == 0)
	83	/* This means some other thread removed the list just after
	84	the pointer has been loaded. Try again. Either the list
	85	is empty or we can retry it. */
	86	continue;
	87
	88	/* Bump the reference counter. */
	89	if (atomic_compare_and_exchange_bool_acq (&__fork_handlers->refcntr,
	90	oldval + 1, oldval))
	91	/* The value changed, try again. */
	92	continue;
	93
	94	/* We bumped the reference counter for the first entry in the
	95	list. That means that none of the following entries will
	96	just go away. The unloading code works in the order of the
	97	list.
	98
	99	While executing the registered handlers we are building a
	100	list of all the entries so that we can go backward later on. */
	101	while (1)
	102	{
	103	/* Execute the handler if there is one. */
	104	if (runp->prepare_handler != NULL)
	105	runp->prepare_handler ();
	106
	107	/* Create a new element for the list. */
	108	struct used_handler *newp
	109	= (struct used_handler ) alloca (sizeof (newp));
	110	newp->handler = runp;
	111	newp->next = allp;
	112	allp = newp;
	113
	114	/* Advance to the next handler. */
	115	runp = runp->next;
	116	if (runp == NULL)
	117	break;
	118
	119	/* Bump the reference counter for the next entry. */
	120	atomic_increment (&runp->refcntr);
	121	}
	122
	123	/* We are done. */
	124	break;
	125	}
	126
	127	__UCLIBC_IO_MUTEX_LOCK_CANCEL_UNSAFE(_stdio_openlist_add_lock);
	128
	129	#ifndef NDEBUG
	130	pid_t ppid = THREAD_GETMEM (THREAD_SELF, tid);
	131	#endif
	132
	133	/* We need to prevent the getpid() code to update the PID field so
	134	that, if a signal arrives in the child very early and the signal
	135	handler uses getpid(), the value returned is correct. */
	136	pid_t parentpid = THREAD_GETMEM (THREAD_SELF, pid);
	137	THREAD_SETMEM (THREAD_SELF, pid, -parentpid);
	138
	139	#ifdef ARCH_FORK
	140	pid = ARCH_FORK ();
	141	#else
	142	# error "ARCH_FORK must be defined so that the CLONE_SETTID flag is used"
	143	pid = INLINE_SYSCALL (fork, 0);
144	#endif
145
146
147	if (pid == 0)
148	{
149	struct pthread *self = THREAD_SELF;
150
151	assert (THREAD_GETMEM (self, tid) != ppid);
152
153	if (__fork_generation_pointer != NULL)
154	*__fork_generation_pointer += 4;
155
156	/* Adjust the PID field for the new process. */
157	THREAD_SETMEM (self, pid, THREAD_GETMEM (self, tid));
158
159	#if HP_TIMING_AVAIL
160	/* The CPU clock of the thread and process have to be set to zero. */
161	hp_timing_t now;
162	HP_TIMING_NOW (now);
163	THREAD_SETMEM (self, cpuclock_offset, now);
164	GL(dl_cpuclock_offset) = now;
165	#endif
166
167	/* Reset the file list. These are recursive mutexes. */
168	fresetlockfiles ();
169
170	/* Reset locks in the I/O code. */
171	STDIO_INIT_MUTEX(_stdio_openlist_add_lock);
172
a032a658 AF	173	/* XXX reset any locks in dynamic loader */
a032a658 AF	174
c68d0fa2 AF	175	/* Run the handlers registered for the child. */
	176	while (allp != NULL)
	177	{
	178	if (allp->handler->child_handler != NULL)
	179	allp->handler->child_handler ();
	180
	181	/* Note that we do not have to wake any possible waiter.
a032a658 AF	182	This is the only thread in the new process. The count
	183	may have been bumped up by other threads doing a fork.
	184	We reset it to 1, to avoid waiting for non-existing
	185	thread(s) to release the count. */
	186	allp->handler->refcntr = 1;
c68d0fa2 AF	187
	188	/* XXX We could at this point look through the object pool
	189	and mark all objects not on the __fork_handlers list as
	190	unused. This is necessary in case the fork() happened
	191	while another thread called dlclose() and that call had
	192	to create a new list. */
	193
	194	allp = allp->next;
	195	}
	196
	197	/* Initialize the fork lock. */
a032a658	198	__fork_lock = LLL_LOCK_INITIALIZER;
c68d0fa2 AF	199	}
	200	else
	201	{
	202	assert (THREAD_GETMEM (THREAD_SELF, tid) == ppid);
	203
	204	/* Restore the PID value. */
	205	THREAD_SETMEM (THREAD_SELF, pid, parentpid);
	206
	207	/* We execute this even if the 'fork' call failed. */
	208	__UCLIBC_IO_MUTEX_UNLOCK_CANCEL_UNSAFE(_stdio_openlist_add_lock);
	209
	210	/* Run the handlers registered for the parent. */
	211	while (allp != NULL)
	212	{
	213	if (allp->handler->parent_handler != NULL)
	214	allp->handler->parent_handler ();
	215
	216	if (atomic_decrement_and_test (&allp->handler->refcntr)
	217	&& allp->handler->need_signal)
a032a658	218	lll_futex_wake (allp->handler->refcntr, 1, LLL_PRIVATE);
c68d0fa2 AF	219
	220	allp = allp->next;
	221	}
	222	}
	223
	224	return pid;
	225	}
	226	weak_alias(__libc_fork,__fork)
	227	libc_hidden_proto(fork)
	228	weak_alias(__libc_fork,fork)
	229	libc_hidden_weak(fork)