1
2 /*--------------------------------------------------------------------*/
3 /*--- Semaphore stuff. sema.c ---*/
4 /*--------------------------------------------------------------------*/
5
6 /*
7 This file is part of Valgrind, a dynamic binary instrumentation
8 framework.
9
10 Copyright (C) 2000-2011 Julian Seward
11 jseward@acm.org
12
13 This program is free software; you can redistribute it and/or
14 modify it under the terms of the GNU General Public License as
15 published by the Free Software Foundation; either version 2 of the
16 License, or (at your option) any later version.
17
18 This program is distributed in the hope that it will be useful, but
19 WITHOUT ANY WARRANTY; without even the implied warranty of
20 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
21 General Public License for more details.
22
23 You should have received a copy of the GNU General Public License
24 along with this program; if not, write to the Free Software
25 Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
26 02111-1307, USA.
27
28 The GNU General Public License is contained in the file COPYING.
29 */
30
31 #include "pub_core_basics.h"
32 #include "pub_core_debuglog.h"
33 #include "pub_core_vki.h"
34 #include "pub_core_libcassert.h"
35 #include "pub_core_libcfile.h"
36 #include "pub_core_libcproc.h" // For VG_(gettid)()
37 #include "priv_sema.h"
38
39 /*
40 Slower (than the removed futex-based sema scheme) but more portable
41 pipe-based token passing scheme.
42 */
43
44 /* Cycle the char passed through the pipe through 'A' .. 'Z' to make
45 it easier to make sense of strace/truss output - makes it possible
46 to see more clearly the change of ownership of the lock. Need to
47 be careful to reinitialise it at fork() time. */
48 static Char sema_char = '!'; /* will cause assertion failures if used
49 before sema_init */
50
ML_(sema_init)51 void ML_(sema_init)(vg_sema_t *sema)
52 {
53 Char buf[2];
54 Int res, r;
55 r = VG_(pipe)(sema->pipe);
56 vg_assert(r == 0);
57
58 vg_assert(sema->pipe[0] != sema->pipe[1]);
59
60 sema->pipe[0] = VG_(safe_fd)(sema->pipe[0]);
61 sema->pipe[1] = VG_(safe_fd)(sema->pipe[1]);
62
63 if (0)
64 VG_(debugLog)(0,"zz","sema_init: %d %d\n", sema->pipe[0],
65 sema->pipe[1]);
66 vg_assert(sema->pipe[0] != sema->pipe[1]);
67
68 sema->owner_lwpid = -1;
69
70 /* create initial token */
71 sema_char = 'A';
72 buf[0] = sema_char;
73 buf[1] = 0;
74 sema_char++;
75 res = VG_(write)(sema->pipe[1], buf, 1);
76 vg_assert(res == 1);
77 }
78
ML_(sema_deinit)79 void ML_(sema_deinit)(vg_sema_t *sema)
80 {
81 vg_assert(sema->owner_lwpid != -1); /* must be initialised */
82 vg_assert(sema->pipe[0] != sema->pipe[1]);
83 VG_(close)(sema->pipe[0]);
84 VG_(close)(sema->pipe[1]);
85 sema->pipe[0] = sema->pipe[1] = -1;
86 sema->owner_lwpid = -1;
87 }
88
89 /* get a token */
ML_(sema_down)90 void ML_(sema_down)( vg_sema_t *sema, Bool as_LL )
91 {
92 Char buf[2];
93 Int ret;
94 Int lwpid = VG_(gettid)();
95
96 vg_assert(sema->owner_lwpid != lwpid); /* can't have it already */
97 vg_assert(sema->pipe[0] != sema->pipe[1]);
98
99 again:
100 buf[0] = buf[1] = 0;
101 ret = VG_(read)(sema->pipe[0], buf, 1);
102
103 if (ret != 1)
104 VG_(debugLog)(0, "scheduler",
105 "VG_(sema_down): read returned %d\n", ret);
106
107 if (ret == -VKI_EINTR)
108 goto again;
109
110 vg_assert(ret == 1); /* should get exactly 1 token */
111 vg_assert(buf[0] >= 'A' && buf[0] <= 'Z');
112 vg_assert(buf[1] == 0);
113
114 if (sema_char == 'Z') sema_char = 'A'; else sema_char++;
115
116 sema->owner_lwpid = lwpid;
117 sema->held_as_LL = as_LL;
118 }
119
120 /* put token back */
ML_(sema_up)121 void ML_(sema_up)( vg_sema_t *sema, Bool as_LL )
122 {
123 Int ret;
124 Char buf[2];
125 vg_assert(as_LL == sema->held_as_LL);
126 buf[0] = sema_char;
127 buf[1] = 0;
128 vg_assert(sema->owner_lwpid != -1); /* must be initialised */
129 vg_assert(sema->pipe[0] != sema->pipe[1]);
130 vg_assert(sema->owner_lwpid == VG_(gettid)()); /* must have it */
131
132 sema->owner_lwpid = 0;
133
134 ret = VG_(write)(sema->pipe[1], buf, 1);
135
136 if (ret != 1)
137 VG_(debugLog)(0, "scheduler",
138 "VG_(sema_up):write returned %d\n", ret);
139
140 vg_assert(ret == 1);
141 }
142
143 /*--------------------------------------------------------------------*/
144 /*--- end ---*/
145 /*--------------------------------------------------------------------*/
146
147
148