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. */
48static Char sema_char = '!'; /* will cause assertion failures if used
49                                before sema_init */
50
51void 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
79void 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 */
90void 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 */
121void 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