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<h2>
<a name="1204432"> </a><font color="#003366" face="Verdana, Arial, Helvetica, sans-serif">6.1 Overview</font>
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<p>
<a name="1204434"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">A semaphore structure <font size=2 face=Courier><strong>semaphore_t</strong></font> contains two pieces of data:</font>
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<p> <font size=2 face="Verdana, Arial, Helvetica, sans-serif"><li ><a name="1204435"> </a>a count of the number of times the semaphore can be taken,</font></p>
<p> <font size=2 face="Verdana, Arial, Helvetica, sans-serif"><li ><a name="1204436"> </a>a queue of tasks waiting to take the semaphore.</font></p>
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<p>
<a name="1204437"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">Semaphores are created using one of the following functions:</font>
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<a name="1204439"> </a><font size=2 face=Courier><strong>semaphore_t* semaphore_create_fifo (int value);<br>void semaphore_init_fifo(semaphore_t *sem, int value);<br>semaphore_t* semaphore_create_priority (int value);<br>void semaphore_init_priority (semaphore_t *sem, int value);<br></strong></font>
<p>
<a name="1204443"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">or if a timeout capability is required while waiting for a semaphore, use the timeout versions of the above functions:</font>
</p>
<a name="1204445"> </a><font size=2 face=Courier><strong>semaphore_t* semaphore_create_fifo_timeout (int value);<br>void semaphore_init_fifo_timeout(semaphore_t *sem, int value);<br>semaphore_t* semaphore_create_priority_timeout (int value);<br>void semaphore_init_priority_timeout(semaphore_t *sem, int value);<br></strong></font>
<p>
<a name="1204449"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">The <font size=2 face=Courier><strong>create_</strong></font> versions of the functions allocate memory for the semaphore automatically, while the <font size=2 face=Courier><strong>init_</strong></font> versions enable the user to specify a pointer to the semaphore, using the data structure <font size=2 face=Courier><strong>semaphore_t</strong></font>.</font>
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<p>
<a name="1204453"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">The semaphores which OS20 provides differ in the way in which tasks are queued. Normally tasks are queued in the order which they call <font size=2 face=Courier><strong>semaphore_wait</strong></font>, in which case this is termed a FIFO semaphore. Semaphores of this type are created using <font size=2 face=Courier><strong>semaphore_create_fifo</strong></font> or <font size=2 face=Courier><strong>semaphore_init_fifo</strong></font> or by using one of the timeout versions of these functions.</font>
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<p>
<a name="1205049"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">However, sometimes it is useful to allow higher priority tasks to jump the queue, so that they are blocked for a minimum amount of time. In this case a second type of semaphore can be used, a priority based semaphore. For this type of semaphore, tasks are queued based on their priority first, and the order which they call <font size=2 face=Courier><strong>semaphore_wait</strong></font> second. Semaphores of this type are created using <font size=2 face=Courier><strong>semaphore_create_priority</strong></font> or <font size=2 face=Courier><strong>semaphore_init_priority</strong></font> or one of the timeout versions of these functions.</font>
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<p>
<a name="1205050"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">Semaphores may be acquired by the function:</font>
</p>
<a name="1205052"> </a><font size=2 face=Courier><strong>void semaphore_wait(semaphore_t* Sem);<br></strong></font>
<p>
<a name="1204458"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">For semaphores created via one of the timeout functions, the following function may also be used:</font>
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<a name="1204460"> </a><font size=2 face=Courier><strong>int semaphore_wait_timeout( semaphore_t* Sem<br>⌨️ 快捷键说明
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