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<div class="title">xSemaphoreTakeRecursive</div> </div>
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<p>semphr. h xSemaphoreTakeRecursive( SemaphoreHandle_t xMutex, TickType_t xBlockTime )</p>
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<p><em>Macro</em> to recursively obtain, or 'take', a mutex type semaphore. The mutex must have previously been created using a call to xSemaphoreCreateRecursiveMutex();</p>
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<p>configUSE_RECURSIVE_MUTEXES must be set to 1 in <a class="el" href="_free_r_t_o_s_config_8h.html">FreeRTOSConfig.h</a> for this macro to be available.</p>
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<p>This macro must not be used on mutexes created using xSemaphoreCreateMutex().</p>
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<p>A mutex used recursively can be 'taken' repeatedly by the owner. The mutex doesn't become available again until the owner has called xSemaphoreGiveRecursive() for each successful 'take' request. For example, if a task successfully 'takes' the same mutex 5 times then the mutex will not be available to any other task until it has also 'given' the mutex back exactly five times.</p>
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<dl class="params"><dt>Parameters</dt><dd>
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<table class="params">
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<tr><td class="paramname">xMutex</td><td>A handle to the mutex being obtained. This is the handle returned by xSemaphoreCreateRecursiveMutex();</td></tr>
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<tr><td class="paramname">xBlockTime</td><td>The time in ticks to wait for the semaphore to become available. The macro portTICK_PERIOD_MS can be used to convert this to a real time. A block time of zero can be used to poll the semaphore. If the task already owns the semaphore then xSemaphoreTakeRecursive() will return immediately no matter what the value of xBlockTime.</td></tr>
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</table>
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</dd>
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</dl>
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<dl class="section return"><dt>Returns</dt><dd>pdTRUE if the semaphore was obtained. pdFALSE if xBlockTime expired without the semaphore becoming available.</dd></dl>
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<p>Example usage: </p><pre>
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SemaphoreHandle_t xMutex = NULL;</pre><pre>// A task that creates a mutex.
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void vATask( void * pvParameters )
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{
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// Create the mutex to guard a shared resource.
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xMutex = xSemaphoreCreateRecursiveMutex();
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}</pre><pre>// A task that uses the mutex.
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void vAnotherTask( void * pvParameters )
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{
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// ... Do other things.</pre><pre> if( xMutex != NULL )
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{
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// See if we can obtain the mutex. If the mutex is not available
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// wait 10 ticks to see if it becomes free.
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if( xSemaphoreTakeRecursive( xSemaphore, ( TickType_t ) 10 ) == pdTRUE )
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{
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// We were able to obtain the mutex and can now access the
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// shared resource.</pre><pre> // ...
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// For some reason due to the nature of the code further calls to
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// xSemaphoreTakeRecursive() are made on the same mutex. In real
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// code these would not be just sequential calls as this would make
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// no sense. Instead the calls are likely to be buried inside
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// a more complex call structure.
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xSemaphoreTakeRecursive( xMutex, ( TickType_t ) 10 );
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xSemaphoreTakeRecursive( xMutex, ( TickType_t ) 10 );</pre><pre> // The mutex has now been 'taken' three times, so will not be
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// available to another task until it has also been given back
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// three times. Again it is unlikely that real code would have
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// these calls sequentially, but instead buried in a more complex
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// call structure. This is just for illustrative purposes.
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xSemaphoreGiveRecursive( xMutex );
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xSemaphoreGiveRecursive( xMutex );
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xSemaphoreGiveRecursive( xMutex );</pre><pre> // Now the mutex can be taken by other tasks.
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}
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else
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{
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// We could not obtain the mutex and can therefore not access
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// the shared resource safely.
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}
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}
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}
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