manu jose
/
6hrslave
B.3 PROGRAM .SLAVE
pt-sem.h@0:9092ea8d9a6c, 2010-12-04 (annotated)
- Committer:
- manujose
- Date:
- Sat Dec 04 05:09:46 2010 +0000
- Revision:
- 0:9092ea8d9a6c
Who changed what in which revision?
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manujose | 0:9092ea8d9a6c | 1 | /* |
manujose | 0:9092ea8d9a6c | 2 | * Copyright (c) 2004, Swedish Institute of Computer Science. |
manujose | 0:9092ea8d9a6c | 3 | * All rights reserved. |
manujose | 0:9092ea8d9a6c | 4 | * |
manujose | 0:9092ea8d9a6c | 5 | * Redistribution and use in source and binary forms, with or without |
manujose | 0:9092ea8d9a6c | 6 | * modification, are permitted provided that the following conditions |
manujose | 0:9092ea8d9a6c | 7 | * are met: |
manujose | 0:9092ea8d9a6c | 8 | * 1. Redistributions of source code must retain the above copyright |
manujose | 0:9092ea8d9a6c | 9 | * notice, this list of conditions and the following disclaimer. |
manujose | 0:9092ea8d9a6c | 10 | * 2. Redistributions in binary form must reproduce the above copyright |
manujose | 0:9092ea8d9a6c | 11 | * notice, this list of conditions and the following disclaimer in the |
manujose | 0:9092ea8d9a6c | 12 | * documentation and/or other materials provided with the distribution. |
manujose | 0:9092ea8d9a6c | 13 | * 3. Neither the name of the Institute nor the names of its contributors |
manujose | 0:9092ea8d9a6c | 14 | * may be used to endorse or promote products derived from this software |
manujose | 0:9092ea8d9a6c | 15 | * without specific prior written permission. |
manujose | 0:9092ea8d9a6c | 16 | * |
manujose | 0:9092ea8d9a6c | 17 | * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND |
manujose | 0:9092ea8d9a6c | 18 | * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE |
manujose | 0:9092ea8d9a6c | 19 | * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE |
manujose | 0:9092ea8d9a6c | 20 | * ARE DISCLAIMED. IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE |
manujose | 0:9092ea8d9a6c | 21 | * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL |
manujose | 0:9092ea8d9a6c | 22 | * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS |
manujose | 0:9092ea8d9a6c | 23 | * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) |
manujose | 0:9092ea8d9a6c | 24 | * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT |
manujose | 0:9092ea8d9a6c | 25 | * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY |
manujose | 0:9092ea8d9a6c | 26 | * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF |
manujose | 0:9092ea8d9a6c | 27 | * SUCH DAMAGE. |
manujose | 0:9092ea8d9a6c | 28 | * |
manujose | 0:9092ea8d9a6c | 29 | * This file is part of the protothreads library. |
manujose | 0:9092ea8d9a6c | 30 | * |
manujose | 0:9092ea8d9a6c | 31 | * Author: Adam Dunkels <adam@sics.se> |
manujose | 0:9092ea8d9a6c | 32 | * |
manujose | 0:9092ea8d9a6c | 33 | * $Id: pt-sem.h,v 1.2 2005/02/24 10:36:59 adam Exp $ |
manujose | 0:9092ea8d9a6c | 34 | */ |
manujose | 0:9092ea8d9a6c | 35 | |
manujose | 0:9092ea8d9a6c | 36 | /** |
manujose | 0:9092ea8d9a6c | 37 | * \addtogroup pt |
manujose | 0:9092ea8d9a6c | 38 | * @{ |
manujose | 0:9092ea8d9a6c | 39 | */ |
manujose | 0:9092ea8d9a6c | 40 | |
manujose | 0:9092ea8d9a6c | 41 | /** |
manujose | 0:9092ea8d9a6c | 42 | * \defgroup ptsem Protothread semaphores |
manujose | 0:9092ea8d9a6c | 43 | * @{ |
manujose | 0:9092ea8d9a6c | 44 | * |
manujose | 0:9092ea8d9a6c | 45 | * This module implements counting semaphores on top of |
manujose | 0:9092ea8d9a6c | 46 | * protothreads. Semaphores are a synchronization primitive that |
manujose | 0:9092ea8d9a6c | 47 | * provide two operations: "wait" and "signal". The "wait" operation |
manujose | 0:9092ea8d9a6c | 48 | * checks the semaphore counter and blocks the thread if the counter |
manujose | 0:9092ea8d9a6c | 49 | * is zero. The "signal" operation increases the semaphore counter but |
manujose | 0:9092ea8d9a6c | 50 | * does not block. If another thread has blocked waiting for the |
manujose | 0:9092ea8d9a6c | 51 | * semaphore that is signalled, the blocked thread will become |
manujose | 0:9092ea8d9a6c | 52 | * runnable again. |
manujose | 0:9092ea8d9a6c | 53 | * |
manujose | 0:9092ea8d9a6c | 54 | * Semaphores can be used to implement other, more structured, |
manujose | 0:9092ea8d9a6c | 55 | * synchronization primitives such as monitors and message |
manujose | 0:9092ea8d9a6c | 56 | * queues/bounded buffers (see below). |
manujose | 0:9092ea8d9a6c | 57 | * |
manujose | 0:9092ea8d9a6c | 58 | * The following example shows how the producer-consumer problem, also |
manujose | 0:9092ea8d9a6c | 59 | * known as the bounded buffer problem, can be solved using |
manujose | 0:9092ea8d9a6c | 60 | * protothreads and semaphores. Notes on the program follow after the |
manujose | 0:9092ea8d9a6c | 61 | * example. |
manujose | 0:9092ea8d9a6c | 62 | * |
manujose | 0:9092ea8d9a6c | 63 | \code |
manujose | 0:9092ea8d9a6c | 64 | #include "pt-sem.h" |
manujose | 0:9092ea8d9a6c | 65 | |
manujose | 0:9092ea8d9a6c | 66 | #define NUM_ITEMS 32 |
manujose | 0:9092ea8d9a6c | 67 | #define BUFSIZE 8 |
manujose | 0:9092ea8d9a6c | 68 | |
manujose | 0:9092ea8d9a6c | 69 | static struct pt_sem mutex, full, empty; |
manujose | 0:9092ea8d9a6c | 70 | |
manujose | 0:9092ea8d9a6c | 71 | PT_THREAD(producer(struct pt *pt)) |
manujose | 0:9092ea8d9a6c | 72 | { |
manujose | 0:9092ea8d9a6c | 73 | static int produced; |
manujose | 0:9092ea8d9a6c | 74 | |
manujose | 0:9092ea8d9a6c | 75 | PT_BEGIN(pt); |
manujose | 0:9092ea8d9a6c | 76 | |
manujose | 0:9092ea8d9a6c | 77 | for(produced = 0; produced < NUM_ITEMS; ++produced) { |
manujose | 0:9092ea8d9a6c | 78 | |
manujose | 0:9092ea8d9a6c | 79 | PT_SEM_WAIT(pt, &full); |
manujose | 0:9092ea8d9a6c | 80 | |
manujose | 0:9092ea8d9a6c | 81 | PT_SEM_WAIT(pt, &mutex); |
manujose | 0:9092ea8d9a6c | 82 | add_to_buffer(produce_item()); |
manujose | 0:9092ea8d9a6c | 83 | PT_SEM_SIGNAL(pt, &mutex); |
manujose | 0:9092ea8d9a6c | 84 | |
manujose | 0:9092ea8d9a6c | 85 | PT_SEM_SIGNAL(pt, &empty); |
manujose | 0:9092ea8d9a6c | 86 | } |
manujose | 0:9092ea8d9a6c | 87 | |
manujose | 0:9092ea8d9a6c | 88 | PT_END(pt); |
manujose | 0:9092ea8d9a6c | 89 | } |
manujose | 0:9092ea8d9a6c | 90 | |
manujose | 0:9092ea8d9a6c | 91 | PT_THREAD(consumer(struct pt *pt)) |
manujose | 0:9092ea8d9a6c | 92 | { |
manujose | 0:9092ea8d9a6c | 93 | static int consumed; |
manujose | 0:9092ea8d9a6c | 94 | |
manujose | 0:9092ea8d9a6c | 95 | PT_BEGIN(pt); |
manujose | 0:9092ea8d9a6c | 96 | |
manujose | 0:9092ea8d9a6c | 97 | for(consumed = 0; consumed < NUM_ITEMS; ++consumed) { |
manujose | 0:9092ea8d9a6c | 98 | |
manujose | 0:9092ea8d9a6c | 99 | PT_SEM_WAIT(pt, &empty); |
manujose | 0:9092ea8d9a6c | 100 | |
manujose | 0:9092ea8d9a6c | 101 | PT_SEM_WAIT(pt, &mutex); |
manujose | 0:9092ea8d9a6c | 102 | consume_item(get_from_buffer()); |
manujose | 0:9092ea8d9a6c | 103 | PT_SEM_SIGNAL(pt, &mutex); |
manujose | 0:9092ea8d9a6c | 104 | |
manujose | 0:9092ea8d9a6c | 105 | PT_SEM_SIGNAL(pt, &full); |
manujose | 0:9092ea8d9a6c | 106 | } |
manujose | 0:9092ea8d9a6c | 107 | |
manujose | 0:9092ea8d9a6c | 108 | PT_END(pt); |
manujose | 0:9092ea8d9a6c | 109 | } |
manujose | 0:9092ea8d9a6c | 110 | |
manujose | 0:9092ea8d9a6c | 111 | PT_THREAD(driver_thread(struct pt *pt)) |
manujose | 0:9092ea8d9a6c | 112 | { |
manujose | 0:9092ea8d9a6c | 113 | static struct pt pt_producer, pt_consumer; |
manujose | 0:9092ea8d9a6c | 114 | |
manujose | 0:9092ea8d9a6c | 115 | PT_BEGIN(pt); |
manujose | 0:9092ea8d9a6c | 116 | |
manujose | 0:9092ea8d9a6c | 117 | PT_SEM_INIT(&empty, 0); |
manujose | 0:9092ea8d9a6c | 118 | PT_SEM_INIT(&full, BUFSIZE); |
manujose | 0:9092ea8d9a6c | 119 | PT_SEM_INIT(&mutex, 1); |
manujose | 0:9092ea8d9a6c | 120 | |
manujose | 0:9092ea8d9a6c | 121 | PT_INIT(&pt_producer); |
manujose | 0:9092ea8d9a6c | 122 | PT_INIT(&pt_consumer); |
manujose | 0:9092ea8d9a6c | 123 | |
manujose | 0:9092ea8d9a6c | 124 | PT_WAIT_THREAD(pt, producer(&pt_producer) & |
manujose | 0:9092ea8d9a6c | 125 | consumer(&pt_consumer)); |
manujose | 0:9092ea8d9a6c | 126 | |
manujose | 0:9092ea8d9a6c | 127 | PT_END(pt); |
manujose | 0:9092ea8d9a6c | 128 | } |
manujose | 0:9092ea8d9a6c | 129 | \endcode |
manujose | 0:9092ea8d9a6c | 130 | * |
manujose | 0:9092ea8d9a6c | 131 | * The program uses three protothreads: one protothread that |
manujose | 0:9092ea8d9a6c | 132 | * implements the consumer, one thread that implements the producer, |
manujose | 0:9092ea8d9a6c | 133 | * and one protothread that drives the two other protothreads. The |
manujose | 0:9092ea8d9a6c | 134 | * program uses three semaphores: "full", "empty" and "mutex". The |
manujose | 0:9092ea8d9a6c | 135 | * "mutex" semaphore is used to provide mutual exclusion for the |
manujose | 0:9092ea8d9a6c | 136 | * buffer, the "empty" semaphore is used to block the consumer is the |
manujose | 0:9092ea8d9a6c | 137 | * buffer is empty, and the "full" semaphore is used to block the |
manujose | 0:9092ea8d9a6c | 138 | * producer is the buffer is full. |
manujose | 0:9092ea8d9a6c | 139 | * |
manujose | 0:9092ea8d9a6c | 140 | * The "driver_thread" holds two protothread state variables, |
manujose | 0:9092ea8d9a6c | 141 | * "pt_producer" and "pt_consumer". It is important to note that both |
manujose | 0:9092ea8d9a6c | 142 | * these variables are declared as <i>static</i>. If the static |
manujose | 0:9092ea8d9a6c | 143 | * keyword is not used, both variables are stored on the stack. Since |
manujose | 0:9092ea8d9a6c | 144 | * protothreads do not store the stack, these variables may be |
manujose | 0:9092ea8d9a6c | 145 | * overwritten during a protothread wait operation. Similarly, both |
manujose | 0:9092ea8d9a6c | 146 | * the "consumer" and "producer" protothreads declare their local |
manujose | 0:9092ea8d9a6c | 147 | * variables as static, to avoid them being stored on the stack. |
manujose | 0:9092ea8d9a6c | 148 | * |
manujose | 0:9092ea8d9a6c | 149 | * |
manujose | 0:9092ea8d9a6c | 150 | */ |
manujose | 0:9092ea8d9a6c | 151 | |
manujose | 0:9092ea8d9a6c | 152 | /** |
manujose | 0:9092ea8d9a6c | 153 | * \file |
manujose | 0:9092ea8d9a6c | 154 | * Couting semaphores implemented on protothreads |
manujose | 0:9092ea8d9a6c | 155 | * \author |
manujose | 0:9092ea8d9a6c | 156 | * Adam Dunkels <adam@sics.se> |
manujose | 0:9092ea8d9a6c | 157 | * |
manujose | 0:9092ea8d9a6c | 158 | */ |
manujose | 0:9092ea8d9a6c | 159 | |
manujose | 0:9092ea8d9a6c | 160 | #ifndef __PT_SEM_H__ |
manujose | 0:9092ea8d9a6c | 161 | #define __PT_SEM_H__ |
manujose | 0:9092ea8d9a6c | 162 | |
manujose | 0:9092ea8d9a6c | 163 | #include "pt.h" |
manujose | 0:9092ea8d9a6c | 164 | |
manujose | 0:9092ea8d9a6c | 165 | struct pt_sem { |
manujose | 0:9092ea8d9a6c | 166 | unsigned int count; |
manujose | 0:9092ea8d9a6c | 167 | }; |
manujose | 0:9092ea8d9a6c | 168 | |
manujose | 0:9092ea8d9a6c | 169 | /** |
manujose | 0:9092ea8d9a6c | 170 | * Initialize a semaphore |
manujose | 0:9092ea8d9a6c | 171 | * |
manujose | 0:9092ea8d9a6c | 172 | * This macro initializes a semaphore with a value for the |
manujose | 0:9092ea8d9a6c | 173 | * counter. Internally, the semaphores use an "unsigned int" to |
manujose | 0:9092ea8d9a6c | 174 | * represent the counter, and therefore the "count" argument should be |
manujose | 0:9092ea8d9a6c | 175 | * within range of an unsigned int. |
manujose | 0:9092ea8d9a6c | 176 | * |
manujose | 0:9092ea8d9a6c | 177 | * \param s (struct pt_sem *) A pointer to the pt_sem struct |
manujose | 0:9092ea8d9a6c | 178 | * representing the semaphore |
manujose | 0:9092ea8d9a6c | 179 | * |
manujose | 0:9092ea8d9a6c | 180 | * \param c (unsigned int) The initial count of the semaphore. |
manujose | 0:9092ea8d9a6c | 181 | * \hideinitializer |
manujose | 0:9092ea8d9a6c | 182 | */ |
manujose | 0:9092ea8d9a6c | 183 | #define PT_SEM_INIT(s, c) (s)->count = c |
manujose | 0:9092ea8d9a6c | 184 | |
manujose | 0:9092ea8d9a6c | 185 | /** |
manujose | 0:9092ea8d9a6c | 186 | * Wait for a semaphore |
manujose | 0:9092ea8d9a6c | 187 | * |
manujose | 0:9092ea8d9a6c | 188 | * This macro carries out the "wait" operation on the semaphore. The |
manujose | 0:9092ea8d9a6c | 189 | * wait operation causes the protothread to block while the counter is |
manujose | 0:9092ea8d9a6c | 190 | * zero. When the counter reaches a value larger than zero, the |
manujose | 0:9092ea8d9a6c | 191 | * protothread will continue. |
manujose | 0:9092ea8d9a6c | 192 | * |
manujose | 0:9092ea8d9a6c | 193 | * \param pt (struct pt *) A pointer to the protothread (struct pt) in |
manujose | 0:9092ea8d9a6c | 194 | * which the operation is executed. |
manujose | 0:9092ea8d9a6c | 195 | * |
manujose | 0:9092ea8d9a6c | 196 | * \param s (struct pt_sem *) A pointer to the pt_sem struct |
manujose | 0:9092ea8d9a6c | 197 | * representing the semaphore |
manujose | 0:9092ea8d9a6c | 198 | * |
manujose | 0:9092ea8d9a6c | 199 | * \hideinitializer |
manujose | 0:9092ea8d9a6c | 200 | */ |
manujose | 0:9092ea8d9a6c | 201 | #define PT_SEM_WAIT(pt, s) \ |
manujose | 0:9092ea8d9a6c | 202 | do { \ |
manujose | 0:9092ea8d9a6c | 203 | PT_WAIT_UNTIL(pt, (s)->count > 0); \ |
manujose | 0:9092ea8d9a6c | 204 | --(s)->count; \ |
manujose | 0:9092ea8d9a6c | 205 | } while(0) |
manujose | 0:9092ea8d9a6c | 206 | |
manujose | 0:9092ea8d9a6c | 207 | /** |
manujose | 0:9092ea8d9a6c | 208 | * Signal a semaphore |
manujose | 0:9092ea8d9a6c | 209 | * |
manujose | 0:9092ea8d9a6c | 210 | * This macro carries out the "signal" operation on the semaphore. The |
manujose | 0:9092ea8d9a6c | 211 | * signal operation increments the counter inside the semaphore, which |
manujose | 0:9092ea8d9a6c | 212 | * eventually will cause waiting protothreads to continue executing. |
manujose | 0:9092ea8d9a6c | 213 | * |
manujose | 0:9092ea8d9a6c | 214 | * \param pt (struct pt *) A pointer to the protothread (struct pt) in |
manujose | 0:9092ea8d9a6c | 215 | * which the operation is executed. |
manujose | 0:9092ea8d9a6c | 216 | * |
manujose | 0:9092ea8d9a6c | 217 | * \param s (struct pt_sem *) A pointer to the pt_sem struct |
manujose | 0:9092ea8d9a6c | 218 | * representing the semaphore |
manujose | 0:9092ea8d9a6c | 219 | * |
manujose | 0:9092ea8d9a6c | 220 | * \hideinitializer |
manujose | 0:9092ea8d9a6c | 221 | */ |
manujose | 0:9092ea8d9a6c | 222 | #define PT_SEM_SIGNAL(pt, s) ++(s)->count |
manujose | 0:9092ea8d9a6c | 223 | |
manujose | 0:9092ea8d9a6c | 224 | #endif /* __PT_SEM_H__ */ |
manujose | 0:9092ea8d9a6c | 225 | |
manujose | 0:9092ea8d9a6c | 226 | /** @} */ |
manujose | 0:9092ea8d9a6c | 227 | /** @} */ |
manujose | 0:9092ea8d9a6c | 228 |