1/* Copyright (C) 2002-2016 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
26struct fork_handler *__fork_handlers;
27
28/* Lock to protect allocation and deallocation of fork handlers. */
29int __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. */
36static struct fork_handler_pool
37{
38 struct fork_handler_pool *next;
39 struct fork_handler mem[NHANDLER];
40} fork_handler_pool;
41
42
43static struct fork_handler *
44fork_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
82int
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}
107libc_hidden_def (__register_atfork)
108
109
110void
111attribute_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
121libc_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}
145