nptl/register-atfork.c

   1 /* Copyright (C) 2002-2017 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
  26 struct fork_handler *__fork_handlers;
  27
  28 /* Lock to protect allocation and deallocation of fork handlers.  */
  29 int __fork_lock = LLL_LOCK_INITIALIZER;
  30
  31
  32 /* Number of pre-allocated handler entries.  */
  33 #define NHANDLER 48
  34
  35 /* Memory pool for fork handler structures.  */
  36 static struct fork_handler_pool
  37 {
  38   struct fork_handler_pool *next;
  39   struct fork_handler mem[NHANDLER];
  40 } fork_handler_pool;
  41
  42
  43 static struct fork_handler *
  44 fork_handler_alloc (void)
  45 {
  46   struct fork_handler_pool *runp = &fork_handler_pool;
  47   struct fork_handler *result = NULL;
  48   unsigned int i;
  49
  50   do
  51     {
  52       /* Search for an empty entry.  */
  53       for (i = 0; i < NHANDLER; ++i)
  54         if (runp->mem[i].refcntr == 0)
  55           goto found;
  56     }
  57   while ((runp = runp->next) != NULL);
  58
  59   /* We have to allocate a new entry.  */
  60   runp = (struct fork_handler_pool *) calloc (1, sizeof (*runp));
  61   if (runp != NULL)
  62     {
  63       /* Enqueue the new memory pool into the list.  */
  64       runp->next = fork_handler_pool.next;
  65       fork_handler_pool.next = runp;
  66
  67       /* We use the last entry on the page.  This means when we start
  68          searching from the front the next time we will find the first
  69          entry unused.  */
  70       i = NHANDLER - 1;
  71
  72     found:
  73       result = &runp->mem[i];
  74       result->refcntr = 1;
  75       result->need_signal = 0;
  76     }
  77
  78   return result;
  79 }
  80
  81
  82 int
  83 __register_atfork (void (*prepare) (void), void (*parent) (void),
  84                    void (*child) (void), void *dso_handle)
  85 {
  86   /* Get the lock to not conflict with other allocations.  */
  87   lll_lock (__fork_lock, LLL_PRIVATE);
  88
  89   struct fork_handler *newp = fork_handler_alloc ();
  90
  91   if (newp != NULL)
  92     {
  93       /* Initialize the new record.  */
  94       newp->prepare_handler = prepare;
  95       newp->parent_handler = parent;
  96       newp->child_handler = child;
  97       newp->dso_handle = dso_handle;
  98
  99       __linkin_atfork (newp);
 100     }
 101
 102   /* Release the lock.  */
 103   lll_unlock (__fork_lock, LLL_PRIVATE);
 104
 105   return newp == NULL ? ENOMEM : 0;
 106 }
 107 libc_hidden_def (__register_atfork)
 108
 109
 110 void
 111 attribute_hidden
 112 __linkin_atfork (struct fork_handler *newp)
 113 {
 114   do
 115     newp->next = __fork_handlers;
 116   while (catomic_compare_and_exchange_bool_acq (&__fork_handlers,
 117                                                 newp, newp->next) != 0);
 118 }
 119
 120
 121 libc_freeres_fn (free_mem)
 122 {
 123   /* Get the lock to not conflict with running forks.  */
 124   lll_lock (__fork_lock, LLL_PRIVATE);
 125
 126   /* No more fork handlers.  */
 127   __fork_handlers = NULL;
 128
 129   /* Free eventually allocated memory blocks for the object pool.  */
 130   struct fork_handler_pool *runp = fork_handler_pool.next;
 131
 132   memset (&fork_handler_pool, '\0', sizeof (fork_handler_pool));
 133
 134   /* Release the lock.  */
 135   lll_unlock (__fork_lock, LLL_PRIVATE);
 136
 137   /* We can free the memory after releasing the lock.  */
 138   while (runp != NULL)
 139     {
 140       struct fork_handler_pool *oldp = runp;
 141       runp = runp->next;
 142       free (oldp);
 143     }
 144 }