1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
|
/* Copyright (C) 2003 Free Software Foundation, Inc.
This file is part of the GNU C Library.
Contributed by Martin Schwidefsky <schwidefsky@de.ibm.com>, 2003.
The GNU C Library is free software; you can redistribute it and/or
modify it under the terms of the GNU Lesser General Public
License as published by the Free Software Foundation; either
version 2.1 of the License, or (at your option) any later version.
The GNU C Library is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
Lesser General Public License for more details.
You should have received a copy of the GNU Lesser General Public
License along with the GNU C Library; if not, write to the Free
Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
02111-1307 USA. */
#include <endian.h>
#include <errno.h>
#include <sysdep.h>
#include <lowlevellock.h>
#include <pthread.h>
#include <pthreadP.h>
#include <shlib-compat.h>
struct _condvar_cleanup_buffer
{
int oldtype;
pthread_cond_t *cond;
pthread_mutex_t *mutex;
};
void
__attribute__ ((visibility ("hidden")))
__condvar_cleanup (void *arg)
{
struct _condvar_cleanup_buffer *cbuffer =
(struct _condvar_cleanup_buffer *) arg;
/* We are going to modify shared data. */
lll_mutex_lock (cbuffer->cond->__data.__lock);
/* This thread is not waiting anymore. Adjust the sequence counters
appropriately. */
++cbuffer->cond->__data.__wakeup_seq;
++cbuffer->cond->__data.__woken_seq;
/* Wake everybody to make sure no condvar signal gets lost. */
#if BYTE_ORDER == LITTLE_ENDIAN
int *futex = ((int *) (&cbuffer->cond->__data.__wakeup_seq));
#elif BYTE_ORDER == BIG_ENDIAN
int *futex = ((int *) (&cbuffer->cond->__data.__wakeup_seq)) + 1;
#else
# error "No valid byte order"
#endif
lll_futex_wake (futex, INT_MAX);
/* We are done. */
lll_mutex_unlock (cbuffer->cond->__data.__lock);
/* Get the mutex before returning unless asynchronous cancellation
is in effect. */
if (!(cbuffer->oldtype & CANCELTYPE_BITMASK))
__pthread_mutex_lock_internal (cbuffer->mutex);
}
int
__pthread_cond_wait (cond, mutex)
pthread_cond_t *cond;
pthread_mutex_t *mutex;
{
struct _pthread_cleanup_buffer buffer;
struct _condvar_cleanup_buffer cbuffer;
int err;
/* Make sure we are along. */
lll_mutex_lock (cond->__data.__lock);
/* Now we can release the mutex. */
err = __pthread_mutex_unlock_internal (mutex);
if (err)
{
lll_mutex_unlock (cond->__data.__lock);
return err;
}
/* We have one new user of the condvar. */
++cond->__data.__total_seq;
/* Prepare structure passed to cancellation handler. */
cbuffer.cond = cond;
cbuffer.mutex = mutex;
/* Before we block we enable cancellation. Therefore we have to
install a cancellation handler. */
__pthread_cleanup_push (&buffer, __condvar_cleanup, &cbuffer);
/* The current values of the wakeup counter. The "woken" counter
must exceed this value. */
unsigned long long int val;
unsigned long long int seq;
val = seq = cond->__data.__wakeup_seq;
/* The futex syscall operates on a 32-bit word. That is fine, we
just use the low 32 bits of the sequence counter. */
#if BYTE_ORDER == LITTLE_ENDIAN
int *futex = ((int *) (&cond->__data.__wakeup_seq));
#elif BYTE_ORDER == BIG_ENDIAN
int *futex = ((int *) (&cond->__data.__wakeup_seq)) + 1;
#else
# error "No valid byte order"
#endif
while (1)
{
/* Prepare to wait. Release the condvar futex. */
lll_mutex_unlock (cond->__data.__lock);
/* Enable asynchronous cancellation. Required by the standard. */
cbuffer.oldtype = __pthread_enable_asynccancel ();
/* Wait until woken by signal or broadcast. Note that we
truncate the 'val' value to 32 bits. */
lll_futex_wait (futex, (unsigned int) val);
/* Disable asynchronous cancellation. */
__pthread_disable_asynccancel (cbuffer.oldtype);
/* We are going to look at shared data again, so get the lock. */
lll_mutex_lock(cond->__data.__lock);
/* Check whether we are eligible for wakeup. */
val = cond->__data.__wakeup_seq;
if (cond->__data.__woken_seq >= seq
&& cond->__data.__woken_seq < val)
break;
}
/* Another thread woken up. */
++cond->__data.__woken_seq;
/* We are done with the condvar. */
lll_mutex_unlock (cond->__data.__lock);
/* The cancellation handling is back to normal, remove the handler. */
__pthread_cleanup_pop (&buffer, 0);
/* Get the mutex before returning. */
return __pthread_mutex_lock_internal (mutex);
}
versioned_symbol (libpthread, __pthread_cond_wait, pthread_cond_wait,
GLIBC_2_3_2);
|
