a00018.html

Protothreads are extremely lightweight stackless threads designed for severely memory constrained s

00115 <span class="comment">  PT_BEGIN(pt);</span>
00116 <span class="comment">  </span>
00117 <span class="comment">  PT_SEM_INIT(&amp;empty, 0);</span>
00118 <span class="comment">  PT_SEM_INIT(&amp;full, BUFSIZE);</span>
00119 <span class="comment">  PT_SEM_INIT(&amp;mutex, 1);</span>
00120 <span class="comment"></span>
00121 <span class="comment">  PT_INIT(&amp;pt_producer);</span>
00122 <span class="comment">  PT_INIT(&amp;pt_consumer);</span>
00123 <span class="comment"></span>
00124 <span class="comment">  PT_WAIT_THREAD(pt, producer(&amp;pt_producer) &amp;</span>
00125 <span class="comment">                     consumer(&amp;pt_consumer));</span>
00126 <span class="comment"></span>
00127 <span class="comment">  PT_END(pt);</span>
00128 <span class="comment">}</span>
00129 <span class="comment"> \endcode</span>
00130 <span class="comment"> *</span>
00131 <span class="comment"> * The program uses three protothreads: one protothread that</span>
00132 <span class="comment"> * implements the consumer, one thread that implements the producer,</span>
00133 <span class="comment"> * and one protothread that drives the two other protothreads. The</span>
00134 <span class="comment"> * program uses three semaphores: "full", "empty" and "mutex". The</span>
00135 <span class="comment"> * "mutex" semaphore is used to provide mutual exclusion for the</span>
00136 <span class="comment"> * buffer, the "empty" semaphore is used to block the consumer is the</span>
00137 <span class="comment"> * buffer is empty, and the "full" semaphore is used to block the</span>
00138 <span class="comment"> * producer is the buffer is full.</span>
00139 <span class="comment"> *</span>
00140 <span class="comment"> * The "driver_thread" holds two protothread state variables,</span>
00141 <span class="comment"> * "pt_producer" and "pt_consumer". It is important to note that both</span>
00142 <span class="comment"> * these variables are declared as &lt;i&gt;static&lt;/i&gt;. If the static</span>
00143 <span class="comment"> * keyword is not used, both variables are stored on the stack. Since</span>
00144 <span class="comment"> * protothreads do not store the stack, these variables may be</span>
00145 <span class="comment"> * overwritten during a protothread wait operation. Similarly, both</span>
00146 <span class="comment"> * the "consumer" and "producer" protothreads declare their local</span>
00147 <span class="comment"> * variables as static, to avoid them being stored on the stack.</span>
00148 <span class="comment"> * </span>
00149 <span class="comment"> *</span>
00150 <span class="comment"> */</span>
00151    <span class="comment"></span>
00152 <span class="comment">/**</span>
00153 <span class="comment"> * \file</span>
00154 <span class="comment"> * Couting semaphores implemented on protothreads</span>
00155 <span class="comment"> * \author</span>
00156 <span class="comment"> * Adam Dunkels &lt;[e-mail]&gt;</span>
00157 <span class="comment"> *</span>
00158 <span class="comment"> */</span>
00159 
00160 <span class="preprocessor">#ifndef __PT_SEM_H__</span>
00161 <span class="preprocessor"></span><span class="preprocessor">#define __PT_SEM_H__</span>
00162 <span class="preprocessor"></span>
00163 <span class="preprocessor">#include "<a class="code" href="a00011.html">pt.h</a>"</span>
00164 
00165 <span class="keyword">struct </span>pt_sem {
00166   <span class="keywordtype">unsigned</span> <span class="keywordtype">int</span> count;
00167 };
00168 <span class="comment"></span>
00169 <span class="comment">/**</span>
00170 <span class="comment"> * Initialize a semaphore</span>
00171 <span class="comment"> *</span>
00172 <span class="comment"> * This macro initializes a semaphore with a value for the</span>
00173 <span class="comment"> * counter. Internally, the semaphores use an "unsigned int" to</span>
00174 <span class="comment"> * represent the counter, and therefore the "count" argument should be</span>
00175 <span class="comment"> * within range of an unsigned int.</span>
00176 <span class="comment"> *</span>
00177 <span class="comment"> * \param s (struct pt_sem *) A pointer to the pt_sem struct</span>
00178 <span class="comment"> * representing the semaphore</span>
00179 <span class="comment"> *</span>
00180 <span class="comment"> * \param c (unsigned int) The initial count of the semaphore.</span>
00181 <span class="comment"> * \hideinitializer</span>
00182 <span class="comment"> */</span>
<a name="l00183"></a><a class="code" href="a00013.html#ga0">00183</a> <span class="preprocessor">#define PT_SEM_INIT(s, c) (s)-&gt;count = c</span>
00184 <span class="preprocessor"></span><span class="comment"></span>
00185 <span class="comment">/**</span>
00186 <span class="comment"> * Wait for a semaphore</span>
00187 <span class="comment"> *</span>
00188 <span class="comment"> * This macro carries out the "wait" operation on the semaphore. The</span>
00189 <span class="comment"> * wait operation causes the protothread to block while the counter is</span>
00190 <span class="comment"> * zero. When the counter reaches a value larger than zero, the</span>
00191 <span class="comment"> * protothread will continue.</span>
00192 <span class="comment"> *</span>
00193 <span class="comment"> * \param pt (struct pt *) A pointer to the protothread (struct pt) in</span>
00194 <span class="comment"> * which the operation is executed.</span>
00195 <span class="comment"> *</span>
00196 <span class="comment"> * \param s (struct pt_sem *) A pointer to the pt_sem struct</span>
00197 <span class="comment"> * representing the semaphore</span>
00198 <span class="comment"> *</span>
00199 <span class="comment"> * \hideinitializer</span>
00200 <span class="comment"> */</span>
<a name="l00201"></a><a class="code" href="a00013.html#ga1">00201</a> <span class="preprocessor">#define PT_SEM_WAIT(pt, s)      \</span>
00202 <span class="preprocessor">  do {                                          \</span>
00203 <span class="preprocessor">    PT_WAIT_UNTIL(pt, (s)-&gt;count &gt; 0);          \</span>
00204 <span class="preprocessor">    --(s)-&gt;count;                               \</span>
00205 <span class="preprocessor">  } while(0)</span>
00206 <span class="preprocessor"></span><span class="comment"></span>
00207 <span class="comment">/**</span>
00208 <span class="comment"> * Signal a semaphore</span>
00209 <span class="comment"> *</span>
00210 <span class="comment"> * This macro carries out the "signal" operation on the semaphore. The</span>
00211 <span class="comment"> * signal operation increments the counter inside the semaphore, which</span>
00212 <span class="comment"> * eventually will cause waiting protothreads to continue executing.</span>
00213 <span class="comment"> *</span>
00214 <span class="comment"> * \param pt (struct pt *) A pointer to the protothread (struct pt) in</span>
00215 <span class="comment"> * which the operation is executed.</span>
00216 <span class="comment"> *</span>
00217 <span class="comment"> * \param s (struct pt_sem *) A pointer to the pt_sem struct</span>
00218 <span class="comment"> * representing the semaphore</span>
00219 <span class="comment"> *</span>
00220 <span class="comment"> * \hideinitializer</span>
00221 <span class="comment"> */</span>
<a name="l00222"></a><a class="code" href="a00013.html#ga2">00222</a> <span class="preprocessor">#define PT_SEM_SIGNAL(pt, s) ++(s)-&gt;count</span>
00223 <span class="preprocessor"></span>
00224 <span class="preprocessor">#endif </span><span class="comment">/* __PT_SEM_H__ */</span>
00225 <span class="comment"></span>
00226 <span class="comment">/** @} */</span><span class="comment"></span>
00227 <span class="comment">/** @} */</span>
00228    
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