summaryrefslogtreecommitdiff
path: root/libpthread/nptl/sysdeps/pthread/pthread_cond_wait.c
blob: 79245b7c13914d6f31d1f516bafcca2f51bcfa08 (plain)
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
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
/* Copyright (C) 2003, 2004 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>


struct _condvar_cleanup_buffer
{
  int oldtype;
  pthread_cond_t *cond;
  pthread_mutex_t *mutex;
  unsigned int bc_seq;
};


void
__attribute__ ((visibility ("hidden")))
__condvar_cleanup (void *arg)
{
  struct _condvar_cleanup_buffer *cbuffer =
    (struct _condvar_cleanup_buffer *) arg;
  unsigned int destroying;

  /* We are going to modify shared data.  */
  lll_mutex_lock (cbuffer->cond->__data.__lock);

  if (cbuffer->bc_seq == cbuffer->cond->__data.__broadcast_seq)
    {
      /* This thread is not waiting anymore.  Adjust the sequence counters
	 appropriately.  */
      ++cbuffer->cond->__data.__wakeup_seq;
      ++cbuffer->cond->__data.__woken_seq;
      ++cbuffer->cond->__data.__futex;
    }

  cbuffer->cond->__data.__nwaiters -= 1 << COND_CLOCK_BITS;

  /* If pthread_cond_destroy was called on this variable already,
     notify the pthread_cond_destroy caller all waiters have left
     and it can be successfully destroyed.  */
  destroying = 0;
  if (cbuffer->cond->__data.__total_seq == -1ULL
      && cbuffer->cond->__data.__nwaiters < (1 << COND_CLOCK_BITS))
    {
      lll_futex_wake (&cbuffer->cond->__data.__nwaiters, 1);
      destroying = 1;
    }

  /* We are done.  */
  lll_mutex_unlock (cbuffer->cond->__data.__lock);

  /* Wake everybody to make sure no condvar signal gets lost.  */
  if (! destroying)
    lll_futex_wake (&cbuffer->cond->__data.__futex, INT_MAX);

  /* Get the mutex before returning unless asynchronous cancellation
     is in effect.  */
  __pthread_mutex_cond_lock (cbuffer->mutex);
}


int
__pthread_cond_wait (
     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_usercnt (mutex, 0);
  if (__builtin_expect (err, 0))
    {
      lll_mutex_unlock (cond->__data.__lock);
      return err;
    }

  /* We have one new user of the condvar.  */
  ++cond->__data.__total_seq;
  ++cond->__data.__futex;
  cond->__data.__nwaiters += 1 << COND_CLOCK_BITS;

  /* Remember the mutex we are using here.  If there is already a
     different address store this is a bad user bug.  Do not store
     anything for pshared condvars.  */
  if (cond->__data.__mutex != (void *) ~0l)
    cond->__data.__mutex = mutex;

  /* 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;
  /* Remember the broadcast counter.  */
  cbuffer.bc_seq = cond->__data.__broadcast_seq;

  do
    {
      unsigned int futex_val = cond->__data.__futex;

      /* 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.  */
      lll_futex_wait (&cond->__data.__futex, futex_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);

      /* If a broadcast happened, we are done.  */
      if (cbuffer.bc_seq != cond->__data.__broadcast_seq)
	goto bc_out;

      /* Check whether we are eligible for wakeup.  */
      val = cond->__data.__wakeup_seq;
    }
  while (val == seq || cond->__data.__woken_seq == val);

  /* Another thread woken up.  */
  ++cond->__data.__woken_seq;

 bc_out:

  cond->__data.__nwaiters -= 1 << COND_CLOCK_BITS;

  /* If pthread_cond_destroy was called on this varaible already,
     notify the pthread_cond_destroy caller all waiters have left
     and it can be successfully destroyed.  */
  if (cond->__data.__total_seq == -1ULL
      && cond->__data.__nwaiters < (1 << COND_CLOCK_BITS))
    lll_futex_wake (&cond->__data.__nwaiters, 1);

  /* 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_cond_lock (mutex);
}
weak_alias(__pthread_cond_wait, pthread_cond_wait)