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<title>使用SDL：线程</title>
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<h1><font color="#8B0000">使用SDL</font></h1>
<h2>线程</h2>
<table border="0" cellpadding="4">
<tr>
<td valign="top"><ul>
<li><strong>创建简单的线程</strong></li>
</ul>
<blockquote>
<p>把一个函数作为SDL_CreateThread()的参数就可以创建一个线程。如果调用成功，该函数就
开始并行运行了，使用自己的栈、寄存器等上下文（context），并能象程序其他部分一样访问内存和文件句柄。
</p>
</blockquote>
</td>
<td valign="top" width="200" bgcolor="#D3D3D3"><strong>提示：</strong><br>
SDL_CreateThread()的第二个参数将被传递给新线程。你可以传入一个放在栈上的值，也可以传入一个供线程使用的数据指针。</td>
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<td valign="top"><font color="#000080"><strong>例程：</strong></font><pre>
<font color="#0000FF">#include</font> "<font color="#000000">SDL_thread.h</font>"
<font color="#008000">int</font> global_data = 0;
<font color="#008000">int</font> thread_func(<font
color="#008000">void *</font>unused)
{
<font color="#008000">int</font> last_value = 0;
<font color="#0000FF">while</font> ( global_data != -1 ) {
<font color="#0000FF">if</font> ( global_data != last_value ) {
printf("数据改变为<font color="#000000"> %d\n</font>", global_data);
last_value = global_data;
}
SDL_Delay(100);
}
printf("<font color="#000000">线程退出</font><font color="#000000">\n</font>");
<font color="#0000FF">return</font>(0);
}
{
SDL_Thread *thread;
<font color="#008000">int</font> i;
thread = SDL_CreateThread(thread_func, NULL);
<font color="#0000FF">if</font> ( thread == NULL ) {
fprintf(stderr, "<font color="#000000">无法创建线程</font><font color="#000000">： %s\n</font>", SDL_GetError());
return;
}
<font color="#0000FF">for</font> ( i=0; i<5; ++i ) {
printf("<font color="#000000">更改数据为</font><font color="#000000"> %d\n</font>", i);
global_data = i;
SDL_Delay(1000);
}
printf("<font color="#000000">通知线程退出</font><font color="#000000">\n</font>");
global_data = -1;
SDL_WaitThread(thread, NULL);
}
</pre>
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</tr>
</table>
<table border="0" cellpadding="4">
<tr>
<td valign="top"><ul>
<li><strong>对资源访问进行同步 </strong></li>
</ul>
<blockquote>
<p>通过创建互斥体（mutex），并将资源用lock
(SDL_mutexP())和unlock (SDL_mutexV())保护起来，就可以防止多个线程同时访问该资源。</p>
</blockquote>
</td>
<td valign="top" width="200" bgcolor="#D3D3D3"><strong>提示：</strong><br>
任何可能会被多个线程访问的数据都应该用mutex保护起来。</td>
</tr>
</table>
<table border="0" cellpadding="50">
<tr>
<td valign="top"><font color="#000080"><strong>例程：</strong></font><pre>
<font color="#0000FF">#include</font> "<font color="#000000">SDL_thread.h</font>"
<font color="#0000FF">#include</font> "<font color="#000000">SDL_mutex.h</font>"
<font color="#008000">int</font> potty = 0;
<font color="#008000">int</font> gotta_go;
<font color="#008000">int</font> thread_func(<font
color="#008000">void *</font>data)
{
SDL_mutex *lock = (SDL_mutex *)data;
<font color="#008000">int</font> times_went;
times_went = 0;
<font color="#0000FF">while</font> ( gotta_go ) {
SDL_mutexP(lock); <font color="#FF0000">/* 锁住potty */</font>
++potty;
printf("<font color="#000000">线程</font><font color="#000000">%d 正在使用potty\n</font>", SDL_ThreadID());
<font color="#0000FF">if</font> ( potty > 1 ) {
printf("<font color="#000000">哦</font><font color="#000000">，有人在用potty!\n</font>");
}
--potty;
SDL_mutexV(lock);
++times_went;
}
printf("好了<font color="#000000">\n</font>");
<font color="#0000FF">return</font>(times_went);
}
{
<font color="#0000FF">const</font> <font color="#008000">int</font> progeny = 5;
SDL_Thread *kids[progeny];
SDL_mutex *lock;
<font color="#008000">int</font> i, lots;
<font color="#FF0000">/* 创建同步锁 */</font>
lock = SDL_CreateMutex();
gotta_go = 1;
<font color="#0000FF">for</font> ( i=0; i<progeny; ++i ) {
kids[i] = SDL_CreateThread(thread_func, lock);
}
SDL_Delay(5*1000);
SDL_mutexP(lock);
printf("<font color="#000000">都完成了吗？\n</font>");
gotta_go = 0;
SDL_mutexV(lock);
<font color="#0000FF">for</font> ( i=0; i<progeny; ++i ) {
SDL_WaitThread(kids[i], &lots);
printf("<font color="#000000">线程</font><font color="#000000"> %d 用过potty %d 次了\n</font>", i+1, lots);
}
SDL_DestroyMutex(lock);
}
</pre>
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