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root/usr/sample/mutex/mutex.c

DEFINITIONS

1. dump_pri
2. thread_run
3. thread_1
4. thread_2
5. thread_3
6. main

   1 /*
   2  * Copyright (c) 2005, Kohsuke Ohtani
   3  * All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  * 3. Neither the name of the author nor the names of any co-contributors
  14  *    may be used to endorse or promote products derived from this software
  15  *    without specific prior written permission.
  16  *
  17  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
  18  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  19  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  20  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
  21  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  22  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  23  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  24  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  25  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  26  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  27  * SUCH DAMAGE.
  28  */
  30 /*
  31  * mutex.c - sample program for mutex with priority inheritance.
  32  */
  34 /*
  35  * Senario:
  36  * This sample shows how the mutex priority is changed when three
  37  * different threads lock two mutexes at same time.
  38  *
  39  * The priority of each thread are as follows.
  40  *    Thread1 - priority 100 (highest)
  41  *    Thread2 - priority 101
  42  *    Thread3 - priority 102
  43  *
  44  * Thread priority and state are changed as follows.
  45  *
  46  *    Action                    Thread 1  Thread 2  Thread 3  Mutex A  Mutex B
  47  *    ------------------------  --------  --------  --------  -------  -------
  48  * 1) Thread 3 locks mutex A    susp/100  susp/101  run /102  owner=3
  49  * 2) Thread 2 locks mutex B    susp/100  run /101  run /102  owner=3  owner=2
  50  * 3) Thread 2 locks mutex A    susp/100  wait/101  run /101* owner=3  owner=2
  51  * 4) Thread 1 locks mutex B    wait/100  wait/100* run /100* owner=3  owner=2
  52  * 5) Thread 3 unlocks mutex A  wait/100  run /100  run /102* owner=2* owner=2
  53  * 6) Thread 2 unlocks mutex B  run /100* run /100  run /102  owner=2  owner=1*
  54  * 7) Thread 2 unlocks mutex A  run /100  run /100  run /102           owner=1
  55  * 8) Thread 1 unlocks mutex B  wait/100  run /101  run /102
  56  *
  57  */
  59 #include <sys/prex.h>
  60 #include <stdio.h>
  62 static char stack[3][1024];
  63 static thread_t th_1, th_2, th_3;
  64 static mutex_t mtx_A, mtx_B;
  66 static void
dump_pri(void)
  68 {
  69         int pri;
  71         if (thread_getpri(th_1, &pri) == 0)
printf("th_1: pri=%d\n", pri);
  74         if (thread_getpri(th_2, &pri) == 0)
printf("th_2: pri=%d\n", pri);
  77         if (thread_getpri(th_3, &pri) == 0)
printf("th_3: pri=%d\n", pri);
  79 }
thread_t
thread_run(void (*start)(void), void *stack)
  83 {
thread_t t;
  86         if (thread_create(task_self(), &t) != 0)
panic("thread_create is failed");
  89         if (thread_load(t, start, stack) != 0)
panic("thread_load is failed");
  92         return t;
  93 }
  95 /*
  96  * Thread 1 - Priority = 100
  97  */
  98 static void
thread_1(void)
 100 {
printf("thread_1: starting\n");
 103         /*
 104          * 4) Lock mutex B
 105          *
 106          * Priority inheritance:
 107          *    Thread 2... Pri 101 -> 100
 108          *    Thread 3... Pri 101 -> 100
 109          */
printf("thread_1: 4) lock B\n");
mutex_lock(&mtx_B);
printf("thread_1: running\n");
dump_pri();
 116         /*
 117          * 8) Unlock mutex B
 118          */
printf("thread_1: 7) unlock B\n");
mutex_unlock(&mtx_B);
dump_pri();
printf("thread_1: exit\n");
thread_terminate(th_1);
 125 }
 127 /*
 128  * Thread 2 - Priority = 101
 129  */
 130 static void
thread_2(void)
 132 {
printf("thread_2: starting\n");
 135         /*
 136          * 2) Lock mutex B
 137          */
printf("thread_2: 2) lock B\n");
mutex_lock(&mtx_B);
dump_pri();
 142         /*
 143          * 3) Lock mutex A (Switch to thread 3)
 144          *
 145          * Priority inheritance:
 146          *    Thread 3... Pri 102 -> 101
 147          */
printf("thread_2: 3) lock A\n");
mutex_lock(&mtx_A);
printf("thread_2: running\n");
dump_pri();
 154         /*
 155          * 6) Unlock mutex B
 156          */
printf("thread_2: 6) unlock B\n");
mutex_unlock(&mtx_B);
dump_pri();
 162         /*
 163          * 7) Unlock mutex A
 164          */
printf("thread_2: 8) unlock A\n");
mutex_unlock(&mtx_A);
printf("thread_2: exit\n");
thread_terminate(th_2);
 170 }
 173 /*
 174  * Thread 3 - Priority = 102
 175  */
 176 static void
thread_3(void)
 178 {
printf("thread_3: start\n");
 181         /*
 182          * 1) Lock mutex A
 183          */
printf("thread_3: 1) lock A\n");
mutex_lock(&mtx_A);
dump_pri();
 188         /*
 189          * Start thread 2
 190          */
thread_resume(th_2);
 193         /*
 194          * Check priority
 195          */
printf("thread_3: running-1\n");
dump_pri();
 199         /*
 200          * Start thread 1
 201          */
thread_resume(th_1);
printf("thread_3: running-2\n");
dump_pri();
 206         /*
 207          * 5) Unlock mutex A
 208          */
printf("thread_3: 5) unlock A\n");
mutex_unlock(&mtx_A);
dump_pri();
printf("thread_3: exit\n");
thread_terminate(th_3);
 215 }
 217 int
main(int argc, char *argv[])
 219 {
printf("Mutex sample program\n");
 222         /*
 223          * Boost priority of this thread
 224          */
thread_setpri(thread_self(), 90);
 227         /*
 228          * Initialize mutexes.
 229          */
mutex_init(&mtx_A);
mutex_init(&mtx_B);
 233         /*
 234          * Create new threads
 235          */
th_1 = thread_run(thread_1, stack[0]+1024);
thread_setpri(th_1, 100);
th_2 = thread_run(thread_2, stack[1]+1024);
thread_setpri(th_2, 101);
th_3 = thread_run(thread_3, stack[2]+1024);
thread_setpri(th_3, 102);
dump_pri();
 247         /*
 248          * Start lowest priority thread
 249          */
thread_resume(th_3);
 252         /*
 253          * Wait...
 254          */
thread_suspend(thread_self());
 257         return 0;
 258 }