nptl/register-atfork.c

   1 /* Copyright (C) 2002-2018 Free Software Foundation, Inc.
   2    This file is part of the GNU C Library.
   3    Contributed by Ulrich Drepper <drepper@redhat.com>, 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, see
  17    <http://www.gnu.org/licenses/>.  */
  18
  19 #include <errno.h>
  20 #include <stdlib.h>
  21 #include <string.h>
  22 #include <fork.h>
  23 #include <atomic.h>
  24
  25 #define DYNARRAY_ELEMENT           struct fork_handler
  26 #define DYNARRAY_STRUCT            fork_handler_list
  27 #define DYNARRAY_PREFIX            fork_handler_list_
  28 #define DYNARRAY_INITIAL_SIZE      48
  29 #include <malloc/dynarray-skeleton.c>
  30
  31 static struct fork_handler_list fork_handlers;
  32 static bool fork_handler_init = false;
  33
  34 static int atfork_lock = LLL_LOCK_INITIALIZER;
  35
  36 int
  37 __register_atfork (void (*prepare) (void), void (*parent) (void),
  38                    void (*child) (void), void *dso_handle)
  39 {
  40   lll_lock (atfork_lock, LLL_PRIVATE);
  41
  42   if (!fork_handler_init)
  43     {
  44       fork_handler_list_init (&fork_handlers);
  45       fork_handler_init = true;
  46     }
  47
  48   struct fork_handler *newp = fork_handler_list_emplace (&fork_handlers);
  49   if (newp != NULL)
  50     {
  51       newp->prepare_handler = prepare;
  52       newp->parent_handler = parent;
  53       newp->child_handler = child;
  54       newp->dso_handle = dso_handle;
  55     }
  56
  57   /* Release the lock.  */
  58   lll_unlock (atfork_lock, LLL_PRIVATE);
  59
  60   return newp == NULL ? ENOMEM : 0;
  61 }
  62 libc_hidden_def (__register_atfork)
  63
  64 static struct fork_handler *
  65 fork_handler_list_find (struct fork_handler_list *fork_handlers,
  66                         void *dso_handle)
  67 {
  68   for (size_t i = 0; i < fork_handler_list_size (fork_handlers); i++)
  69     {
  70       struct fork_handler *elem = fork_handler_list_at (fork_handlers, i);
  71       if (elem->dso_handle == dso_handle)
  72         return elem;
  73     }
  74   return NULL;
  75 }
  76
  77 void
  78 __unregister_atfork (void *dso_handle)
  79 {
  80   lll_lock (atfork_lock, LLL_PRIVATE);
  81
  82   struct fork_handler *first = fork_handler_list_find (&fork_handlers,
  83                                                        dso_handle);
  84   /* Removing is done by shifting the elements in the way the elements
  85      that are not to be removed appear in the beginning in dynarray.
  86      This avoid the quadradic run-time if a naive strategy to remove and
  87      shift one element at time.  */
  88   if (first != NULL)
  89     {
  90       struct fork_handler *new_end = first;
  91       first++;
  92       for (; first != fork_handler_list_end (&fork_handlers); ++first)
  93         {
  94           if (first->dso_handle != dso_handle)
  95             {
  96               *new_end = *first;
  97               ++new_end;
  98             }
  99         }
 100
 101       ptrdiff_t removed = first - new_end;
 102       for (size_t i = 0; i < removed; i++)
 103         fork_handler_list_remove_last (&fork_handlers);
 104     }
 105
 106   lll_unlock (atfork_lock, LLL_PRIVATE);
 107 }
 108
 109 void
 110 __run_fork_handlers (enum __run_fork_handler_type who)
 111 {
 112   struct fork_handler *runp;
 113
 114   if (who == atfork_run_prepare)
 115     {
 116       lll_lock (atfork_lock, LLL_PRIVATE);
 117       size_t sl = fork_handler_list_size (&fork_handlers);
 118       for (size_t i = sl; i > 0; i--)
 119         {
 120           runp = fork_handler_list_at (&fork_handlers, i - 1);
 121           if (runp->prepare_handler != NULL)
 122             runp->prepare_handler ();
 123         }
 124     }
 125   else
 126     {
 127       size_t sl = fork_handler_list_size (&fork_handlers);
 128       for (size_t i = 0; i < sl; i++)
 129         {
 130           runp = fork_handler_list_at (&fork_handlers, i);
 131           if (who == atfork_run_child && runp->child_handler)
 132             runp->child_handler ();
 133           else if (who == atfork_run_parent && runp->parent_handler)
 134             runp->parent_handler ();
 135         }
 136       lll_unlock (atfork_lock, LLL_PRIVATE);
 137     }
 138 }
 139
 140
 141 libc_freeres_fn (free_mem)
 142 {
 143   lll_lock (atfork_lock, LLL_PRIVATE);
 144
 145   fork_handler_list_free (&fork_handlers);
 146
 147   lll_unlock (atfork_lock, LLL_PRIVATE);
 148 }