1/*
2   An example that shows how to implement the monitor synchronization concept.
3   See also http://en.wikipedia.org/wiki/Monitor_(synchronization) for more
4   information about this concept.
5
6   ----------------------------------------------------------------
7
8   Notice that the following BSD-style license applies to this one
9   file (monitor_example.cpp) only.  The rest of Valgrind is licensed
10   under the terms of the GNU General Public License, version 2,
11   unless otherwise indicated.  See the COPYING file in the source
12   distribution for details.
13
14   ----------------------------------------------------------------
15
16   This file is part of DRD, a heavyweight Valgrind tool for detecting
17   errors in multithreaded programs.
18
19   Copyright (C) 2008-2009 Bart Van Assche. All rights reserved.
20
21   Redistribution and use in source and binary forms, with or without
22   modification, are permitted provided that the following conditions
23   are met:
24
25   1. Redistributions of source code must retain the above copyright
26      notice, this list of conditions and the following disclaimer.
27
28   2. The origin of this software must not be misrepresented; you must
29      not claim that you wrote the original software.  If you use this
30      software in a product, an acknowledgment in the product
31      documentation would be appreciated but is not required.
32
33   3. Altered source versions must be plainly marked as such, and must
34      not be misrepresented as being the original software.
35
36   4. The name of the author may not be used to endorse or promote
37      products derived from this software without specific prior written
38      permission.
39
40   THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS
41   OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
42   WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
43   ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
44   DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
45   DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE
46   GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
47   INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
48   WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
49   NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
50   SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
51
52   ----------------------------------------------------------------
53
54   Notice that the above BSD-style license applies to this one
55   file (monitor_example.cpp) only.  The rest of Valgrind is licensed
56   under the terms of the GNU General Public License, version 2,
57   unless otherwise indicated.  See the COPYING file in the source
58   distribution for details.
59
60   ----------------------------------------------------------------
61*/
62
63
64#define _GNU_SOURCE 1
65
66
67#include "config.h"
68#include <cassert>
69#include <iostream>
70#include <pthread.h>
71
72
73class Monitor
74{
75public:
76  Monitor()
77    : m_mutex()
78    , m_cond()
79    , m_owner()
80    , m_recursion_count()
81  {
82    pthread_mutexattr_t mutexattr;
83    pthread_mutexattr_init(&mutexattr);
84    pthread_mutexattr_settype(&mutexattr, PTHREAD_MUTEX_RECURSIVE);
85    pthread_mutex_init(&m_mutex, &mutexattr);
86    pthread_mutexattr_destroy(&mutexattr);
87    pthread_condattr_t condattr;
88    pthread_condattr_init(&condattr);
89#if defined(HAVE_PTHREAD_CONDATTR_SETCLOCK)
90    pthread_condattr_setclock(&condattr, CLOCK_MONOTONIC);
91#endif
92    pthread_cond_init(&m_cond, &condattr);
93    pthread_condattr_destroy(&condattr);
94  }
95  ~Monitor()
96  {
97    assert(m_recursion_count == 0);
98    pthread_cond_destroy(&m_cond);
99    pthread_mutex_destroy(&m_mutex);
100  }
101  void lock()
102  {
103    pthread_mutex_lock(&m_mutex);
104    assert(m_recursion_count >= 0);
105    if (++m_recursion_count == 1)
106    {
107      m_owner = pthread_self();
108    }
109  }
110  void unlock()
111  {
112    m_recursion_count--;
113    assert(m_recursion_count >= 0);
114    pthread_mutex_unlock(&m_mutex);
115  }
116  void wait()
117  {
118    assert(m_recursion_count == 1);
119    assert(m_owner == pthread_self());
120    m_recursion_count--;
121    pthread_cond_wait(&m_cond, &m_mutex);
122    m_recursion_count++;
123    m_owner = pthread_self();
124  }
125  void signal()
126  {
127    assert(m_recursion_count > 0);
128    pthread_cond_signal(&m_cond);
129  }
130  void broadcast_signal()
131  {
132    assert(m_recursion_count > 0);
133    pthread_cond_broadcast(&m_cond);
134  }
135  bool is_locked_by_self()
136  {
137    bool result;
138    pthread_mutex_lock(&m_mutex);
139    result = m_recursion_count > 0 && m_owner == pthread_self();
140    pthread_mutex_unlock(&m_mutex);
141    return result;
142  }
143
144private:
145  Monitor(const Monitor&);
146  Monitor& operator=(const Monitor&);
147
148  pthread_mutex_t m_mutex;
149  pthread_cond_t  m_cond;
150  pthread_t       m_owner;
151  int             m_recursion_count;
152};
153
154
155class ScopedLock
156{
157public:
158  ScopedLock(Monitor& m)
159    : m_monitor(m)
160    , m_locked(false)
161  { lock(); }
162  ~ScopedLock()
163  { if (m_locked) unlock(); }
164  void lock()
165  { assert(! m_locked); m_monitor.lock(); m_locked = true; }
166  void unlock()
167  { assert(m_locked); m_locked = false; m_monitor.unlock(); }
168
169private:
170  ScopedLock(const ScopedLock&);
171  ScopedLock& operator=(const ScopedLock&);
172
173  Monitor& m_monitor;
174  bool     m_locked;
175};
176
177
178class StateVariable
179{
180public:
181  StateVariable()
182    : m_state()
183  { }
184  int get()
185  {
186    ScopedLock sl(m_monitor);
187    return m_state;
188  }
189  void set(const int state)
190  {
191    ScopedLock sl(m_monitor);
192    m_state = state;
193    m_monitor.signal();
194  }
195  void wait(const int state)
196  {
197    ScopedLock sl(m_monitor);
198    while (m_state != state)
199      m_monitor.wait();
200  }
201
202private:
203  Monitor m_monitor;
204  int     m_state;
205};
206
207
208static StateVariable s_sv;
209
210
211static void* thread_func(void*)
212{
213  s_sv.wait(1);
214  s_sv.set(2);
215  s_sv.wait(3);
216  s_sv.set(4);
217  return 0;
218}
219
220int main(int, char**)
221{
222  pthread_t tid;
223  pthread_create(&tid, 0, thread_func, 0);
224  s_sv.set(1);
225  s_sv.wait(2);
226  s_sv.set(3);
227  s_sv.wait(4);
228  pthread_join(tid, 0);
229  std::cerr << "Finished successfully.\n";
230  return 0;
231}
232