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28f540f4 | 1 | /* Support for chains recording users of a resource; `struct hurd_userlink'. |
dff8da6b | 2 | Copyright (C) 1994-2024 Free Software Foundation, Inc. |
c84142e8 | 3 | This file is part of the GNU C Library. |
28f540f4 | 4 | |
c84142e8 | 5 | The GNU C Library is free software; you can redistribute it and/or |
41bdb6e2 AJ |
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. | |
28f540f4 | 9 | |
c84142e8 UD |
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 | |
41bdb6e2 | 13 | Lesser General Public License for more details. |
28f540f4 | 14 | |
41bdb6e2 | 15 | You should have received a copy of the GNU Lesser General Public |
59ba27a6 | 16 | License along with the GNU C Library; if not, see |
5a82c748 | 17 | <https://www.gnu.org/licenses/>. */ |
28f540f4 RM |
18 | |
19 | #ifndef _HURD_USERLINK_H | |
20 | ||
21 | #define _HURD_USERLINK_H 1 | |
22 | #include <features.h> | |
23 | ||
24 | #define __need_NULL | |
25 | #include <stddef.h> | |
26 | ||
3403cb7d ST |
27 | #if defined __USE_EXTERN_INLINES && defined _LIBC |
28 | # if IS_IN (libc) | |
29 | # include <hurd/signal.h> | |
30 | # endif | |
31 | #endif | |
1474b80f RM |
32 | #include <setjmp.h> |
33 | ||
34 | ||
35 | /* This structure records a link in two doubly-linked lists. | |
36 | We call these the per-resource user list and the per-thread | |
c84142e8 | 37 | active-resource list. |
1474b80f RM |
38 | |
39 | Users of a given resource are recorded by their presence in a list | |
40 | associated with that resource. A user attaches his own link (in local | |
41 | storage on his stack) to a shared chain at the time he begins using some | |
42 | resource. When finished with that resource, the user removes his link | |
43 | from the chain. If his link is the last (there are no other users of | |
44 | the resource), and his chain has been detached from the shared cell (the | |
45 | resource in the cell has been replaced), then the user deallocates the | |
46 | resource that he used. | |
47 | ||
48 | All uses of shared resources by a single thread are linked together by | |
49 | its `active-resource' list; the head of this list is stored in the | |
50 | per-thread sigstate structure. When the thread makes a non-local exit | |
51 | (i.e. longjmp), it will examine its active-resource list, and each link | |
52 | residing in a stack frame being jumped out of will be unlinked from both | |
53 | the resource's user list and the thread's active-resource list, and | |
54 | deallocate the resource if that was the last user link for that resource. | |
55 | ||
56 | NOTE: Access to a thread's active-resource list must always be done | |
57 | inside a signal-proof critical section; the functions in this file | |
58 | assume they are called inside a critical section, and do no locking of | |
59 | their own. Also important: the longjmp cleanup relies on all userlink | |
60 | structures residing on the stack of the using thread. */ | |
28f540f4 RM |
61 | |
62 | struct hurd_userlink | |
63 | { | |
1474b80f RM |
64 | struct |
65 | { | |
66 | struct hurd_userlink *next, **prevp; | |
67 | } resource, thread; | |
68 | ||
69 | /* This function is called when a non-local exit | |
70 | unwinds the frame containing this link. */ | |
71 | void (*cleanup) (void *cleanup_data, jmp_buf env, int val); | |
72 | void *cleanup_data; | |
28f540f4 RM |
73 | }; |
74 | ||
75 | ||
6f9dc08b | 76 | #ifndef _HURD_USERLINK_H_EXTERN_INLINE |
b037a293 | 77 | #define _HURD_USERLINK_H_EXTERN_INLINE __extern_inline |
28f540f4 RM |
78 | #endif |
79 | ||
80 | ||
81 | /* Attach LINK to the chain of users at *CHAINP. */ | |
82 | ||
28f6186f ST |
83 | extern void |
84 | _hurd_userlink_link (struct hurd_userlink **chainp, | |
85 | struct hurd_userlink *link); | |
86 | ||
87 | #if defined __USE_EXTERN_INLINES && defined _LIBC | |
2f8902cc | 88 | # if IS_IN (libc) |
6f9dc08b | 89 | _HURD_USERLINK_H_EXTERN_INLINE void |
28f540f4 RM |
90 | _hurd_userlink_link (struct hurd_userlink **chainp, |
91 | struct hurd_userlink *link) | |
92 | { | |
1474b80f RM |
93 | struct hurd_userlink **thread_chainp; |
94 | ||
95 | link->resource.next = *chainp; | |
96 | if (link->resource.next) | |
5e75b232 | 97 | link->resource.next->resource.prevp = &link->resource.next; |
1474b80f | 98 | link->resource.prevp = chainp; |
28f540f4 | 99 | *chainp = link; |
1474b80f | 100 | |
2ce0481d ST |
101 | if (!__LIBC_NO_TLS ()) |
102 | { | |
103 | /* Also chain it on the current thread's list of active resources. */ | |
104 | thread_chainp = &_hurd_self_sigstate ()->active_resources; | |
105 | link->thread.next = *thread_chainp; | |
106 | if (link->thread.next) | |
107 | link->thread.next->thread.prevp = &link->thread.next; | |
108 | link->thread.prevp = thread_chainp; | |
109 | *thread_chainp = link; | |
110 | } | |
28f540f4 | 111 | } |
2f8902cc | 112 | # endif |
28f6186f | 113 | #endif |
28f540f4 RM |
114 | |
115 | ||
1474b80f RM |
116 | /* Detach LINK from its chain. Returns nonzero iff this was the |
117 | last user of the resource and it should be deallocated. */ | |
28f540f4 | 118 | |
28f6186f ST |
119 | extern int _hurd_userlink_unlink (struct hurd_userlink *link); |
120 | ||
121 | #if defined __USE_EXTERN_INLINES && defined _LIBC | |
2f8902cc | 122 | # if IS_IN (libc) |
6f9dc08b | 123 | _HURD_USERLINK_H_EXTERN_INLINE int |
28f540f4 RM |
124 | _hurd_userlink_unlink (struct hurd_userlink *link) |
125 | { | |
1474b80f RM |
126 | /* We should deallocate the resource used if this chain has been detached |
127 | from the cell (and thus has a nil `prevp'), and there is no next link | |
128 | representing another user reference to the same resource. */ | |
129 | int dealloc = ! link->resource.next && ! link->resource.prevp; | |
28f540f4 RM |
130 | |
131 | /* Remove our link from the chain of current users. */ | |
1474b80f RM |
132 | if (link->resource.prevp) |
133 | *link->resource.prevp = link->resource.next; | |
134 | if (link->resource.next) | |
135 | link->resource.next->resource.prevp = link->resource.prevp; | |
136 | ||
2ce0481d ST |
137 | if (!__LIBC_NO_TLS ()) |
138 | { | |
139 | /* Remove our link from the chain of currently active resources | |
140 | for this thread. */ | |
141 | *link->thread.prevp = link->thread.next; | |
142 | if (link->thread.next) | |
143 | link->thread.next->thread.prevp = link->thread.prevp; | |
144 | } | |
28f540f4 RM |
145 | |
146 | return dealloc; | |
147 | } | |
2f8902cc | 148 | # endif |
28f6186f | 149 | #endif |
28f540f4 | 150 | |
7fa495cd ST |
151 | /* Relocate LINK to NEW_LINK. |
152 | To be used when e.g. reallocating a link array. */ | |
153 | ||
154 | extern void _hurd_userlink_move (struct hurd_userlink *new_link, | |
155 | struct hurd_userlink *link); | |
156 | ||
157 | #if defined __USE_EXTERN_INLINES && defined _LIBC | |
158 | # if IS_IN (libc) | |
159 | _HURD_USERLINK_H_EXTERN_INLINE void | |
160 | _hurd_userlink_move (struct hurd_userlink *new_link, | |
161 | struct hurd_userlink *link) | |
162 | { | |
163 | *new_link = *link; | |
164 | ||
165 | if (new_link->resource.next != NULL) | |
166 | new_link->resource.next->resource.prevp = &new_link->resource.next; | |
278fdabd | 167 | *new_link->resource.prevp = new_link; |
7fa495cd | 168 | |
2ce0481d ST |
169 | if (!__LIBC_NO_TLS ()) |
170 | { | |
171 | if (new_link->thread.next != NULL) | |
172 | new_link->thread.next->thread.prevp = &new_link->thread.next; | |
173 | *new_link->thread.prevp = new_link; | |
174 | } | |
7fa495cd ST |
175 | } |
176 | # endif | |
177 | #endif | |
28f540f4 RM |
178 | |
179 | /* Clear all users from *CHAINP. Call this when the resource *CHAINP | |
180 | protects is changing. If the return value is nonzero, no users are on | |
181 | the chain and the caller should deallocate the resource. If the return | |
182 | value is zero, someone is still using the resource and they will | |
183 | deallocate it when they are finished. */ | |
184 | ||
28f6186f ST |
185 | extern int _hurd_userlink_clear (struct hurd_userlink **chainp); |
186 | ||
187 | #if defined __USE_EXTERN_INLINES && defined _LIBC | |
2f8902cc | 188 | # if IS_IN (libc) |
6f9dc08b | 189 | _HURD_USERLINK_H_EXTERN_INLINE int |
28f540f4 RM |
190 | _hurd_userlink_clear (struct hurd_userlink **chainp) |
191 | { | |
192 | if (*chainp == NULL) | |
193 | return 1; | |
194 | ||
195 | /* Detach the chain of current users from the cell. The last user to | |
196 | remove his link from that chain will deallocate the old resource. */ | |
1474b80f | 197 | (*chainp)->resource.prevp = NULL; |
28f540f4 RM |
198 | *chainp = NULL; |
199 | return 0; | |
200 | } | |
2f8902cc | 201 | # endif |
28f6186f | 202 | #endif |
28f540f4 RM |
203 | |
204 | #endif /* hurd/userlink.h */ |