about summary refs log tree commit diff
path: root/nptl/register-atfork.c
blob: 5ff1c1be8cd0432c45f9726625922e44c1c1b173 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
/* Copyright (C) 2002-2018 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <drepper@redhat.com>, 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, see
   <http://www.gnu.org/licenses/>.  */

#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <fork.h>
#include <atomic.h>

#define DYNARRAY_ELEMENT           struct fork_handler
#define DYNARRAY_STRUCT            fork_handler_list
#define DYNARRAY_PREFIX            fork_handler_list_
#define DYNARRAY_INITIAL_SIZE      48
#include <malloc/dynarray-skeleton.c>

static struct fork_handler_list fork_handlers;
static bool fork_handler_init = false;

static int atfork_lock = LLL_LOCK_INITIALIZER;

int
__register_atfork (void (*prepare) (void), void (*parent) (void),
		   void (*child) (void), void *dso_handle)
{
  lll_lock (atfork_lock, LLL_PRIVATE);

  if (!fork_handler_init)
    {
      fork_handler_list_init (&fork_handlers);
      fork_handler_init = true;
    }

  struct fork_handler *newp = fork_handler_list_emplace (&fork_handlers);
  if (newp != NULL)
    {
      newp->prepare_handler = prepare;
      newp->parent_handler = parent;
      newp->child_handler = child;
      newp->dso_handle = dso_handle;
    }

  /* Release the lock.  */
  lll_unlock (atfork_lock, LLL_PRIVATE);

  return newp == NULL ? ENOMEM : 0;
}
libc_hidden_def (__register_atfork)

static struct fork_handler *
fork_handler_list_find (struct fork_handler_list *fork_handlers,
			void *dso_handle)
{
  for (size_t i = 0; i < fork_handler_list_size (fork_handlers); i++)
    {
      struct fork_handler *elem = fork_handler_list_at (fork_handlers, i);
      if (elem->dso_handle == dso_handle)
	return elem;
    }
  return NULL;
}

void
__unregister_atfork (void *dso_handle)
{
  lll_lock (atfork_lock, LLL_PRIVATE);

  struct fork_handler *first = fork_handler_list_find (&fork_handlers,
						       dso_handle);
  /* Removing is done by shifting the elements in the way the elements
     that are not to be removed appear in the beginning in dynarray.
     This avoid the quadradic run-time if a naive strategy to remove and
     shift one element at time.  */
  if (first != NULL)
    {
      struct fork_handler *new_end = first;
      first++;
      for (; first != fork_handler_list_end (&fork_handlers); ++first)
	{
	  if (first->dso_handle != dso_handle)
	    {
	      *new_end = *first;
	      ++new_end;
	    }
	}

      ptrdiff_t removed = first - new_end;
      for (size_t i = 0; i < removed; i++)
	fork_handler_list_remove_last (&fork_handlers);
    }

  lll_unlock (atfork_lock, LLL_PRIVATE);
}

void
__run_fork_handlers (enum __run_fork_handler_type who)
{
  struct fork_handler *runp;

  if (who == atfork_run_prepare)
    {
      lll_lock (atfork_lock, LLL_PRIVATE);
      size_t sl = fork_handler_list_size (&fork_handlers);
      for (size_t i = sl; i > 0; i--)
	{
	  runp = fork_handler_list_at (&fork_handlers, i - 1);
	  if (runp->prepare_handler != NULL)
	    runp->prepare_handler ();
	}
    }
  else
    {
      size_t sl = fork_handler_list_size (&fork_handlers);
      for (size_t i = 0; i < sl; i++)
	{
	  runp = fork_handler_list_at (&fork_handlers, i);
	  if (who == atfork_run_child && runp->child_handler)
	    runp->child_handler ();
	  else if (who == atfork_run_parent && runp->parent_handler)
	    runp->parent_handler ();
	}
      lll_unlock (atfork_lock, LLL_PRIVATE);
    }
}


libc_freeres_fn (free_mem)
{
  lll_lock (atfork_lock, LLL_PRIVATE);

  fork_handler_list_free (&fork_handlers);

  lll_unlock (atfork_lock, LLL_PRIVATE);
}