diff --git a/Demo/Common/Minimal/recmutex.c b/Demo/Common/Minimal/recmutex.c
index fea1d32c4..a1ceb4485 100644
--- a/Demo/Common/Minimal/recmutex.c
+++ b/Demo/Common/Minimal/recmutex.c
@@ -37,11 +37,10 @@
/*
The tasks defined on this page demonstrate the use of recursive mutexes.
- All mutexes are created using a call to xSemaphoreCreateMutex(). For
- recursive mutex functionality the created mutex should then be manipulated
+ For recursive mutex functionality the created mutex should be created using
+ xSemaphoreCreateRecursiveMutex(), then be manipulated
using the xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() API
- functions. Recursive mutexes must NOT be passed as a parameter to the
- standard mutex API functions xSemaphoreTake() and xSemaphoreGive().
+ functions.
This demo creates three tasks all of which access the same recursive mutex:
diff --git a/Source/include/semphr.h b/Source/include/semphr.h
index b5c61e04c..dc236a599 100644
--- a/Source/include/semphr.h
+++ b/Source/include/semphr.h
@@ -99,18 +99,21 @@ typedef xQueueHandle xSemaphoreHandle;
* portTickType xBlockTime
* )
*
- * Macro to obtain a semaphore. The semaphore must of been created using
- * vSemaphoreCreateBinary ().
+ * Macro to obtain a semaphore. The semaphore must have previously been
+ * created with a call to vSemaphoreCreateBinary(), xSemaphoreCreateMutex() or
+ * xSemaphoreCreateCounting().
*
- * @param xSemaphore A handle to the semaphore being obtained. This is the
- * handle returned by vSemaphoreCreateBinary ();
+ * @param xSemaphore A handle to the semaphore being taken - obtained when
+ * the semaophore was created.
*
* @param xBlockTime The time in ticks to wait for the semaphore to become
* available. The macro portTICK_RATE_MS can be used to convert this to a
- * real time. A block time of zero can be used to poll the semaphore.
+ * real time. A block time of zero can be used to poll the semaphore. A block
+ * time of portMAX_DELAY can be used to block indefinately (provided
+ * INCLUDE_vTaskSuspend is set to 1 in FreeRTOSConfig.h).
*
- * @return pdTRUE if the semaphore was obtained. pdFALSE if xBlockTime
- * expired without the semaphore becoming available.
+ * @return pdTRUE if the semaphore was obtained. pdFALSE
+ * if xBlockTime expired without the semaphore becoming available.
*
* Example usage:
@@ -156,6 +159,100 @@ typedef xQueueHandle xSemaphoreHandle;
*/
#define xSemaphoreTake( xSemaphore, xBlockTime ) xQueueGenericReceive( ( xQueueHandle ) xSemaphore, NULL, xBlockTime, pdFALSE )
+/**
+ * semphr. h
+ * xSemaphoreTakeRecursive(
+ * xSemaphoreHandle xMutex,
+ * portTickType xBlockTime
+ * )
+ *
+ * Macro to recursively obtain, or 'take', a mutex type semaphore.
+ * The mutex must have previously been created using a call to
+ * xSemaphoreCreateRecursiveMutex();
+ *
+ * configUSE_RECURSIVE_MUTEXES must be set to 1 in FreeRTOSConfig.h for this
+ * macro to be available.
+ *
+ * This macro must not be used on mutexes created using xSemaphoreCreateMutex().
+ *
+ * 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 avilable to any other task until it has also 'given' the mutex back
+ * exactly five times.
+ *
+ * @param xMutex A handle to the mutex being obtained. This is the
+ * handle returned by xSemaphoreCreateMutex();
+ *
+ * @param xBlockTime The time in ticks to wait for the semaphore to become
+ * available. The macro portTICK_RATE_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 nomatter what the value of xBlockTime.
+ *
+ * @return pdTRUE if the semaphore was obtained. pdFALSE if xBlockTime
+ * expired without the semaphore becoming available.
+ *
+ * Example usage:
+
+ xSemaphoreHandle xMutex = NULL;
+
+ // A task that creates a mutex.
+ void vATask( void * pvParameters )
+ {
+ // Create the mutex to guard a shared resource.
+ xMutex = xSemaphoreCreateRecursiveMutex();
+ }
+
+ // A task that uses the mutex.
+ void vAnotherTask( void * pvParameters )
+ {
+ // ... Do other things.
+
+ if( xMutex != NULL )
+ {
+ // See if we can obtain the mutex. If the mutex is not available
+ // wait 10 ticks to see if it becomes free.
+ if( xSemaphoreTakeRecursive( xSemaphore, ( portTickType ) 10 ) == pdTRUE )
+ {
+ // We were able to obtain the mutex and can now access the
+ // shared resource.
+
+ // ...
+ // For some reason due to the nature of the code further calls to
+ // xSemaphoreTakeRecursive() are made on the same mutex. In real
+ // code these would not be just sequential calls as this would make
+ // no sense. Instead the calls are likely to be buried inside
+ // a more complex call structure.
+ xSemaphoreTakeRecursive( xSemaphore, ( portTickType ) 10 );
+ xSemaphoreTakeRecursive( xSemaphore, ( portTickType ) 10 );
+
+ // The mutex has now been 'taken' three times, so will not be
+ // available to another task until it has also been given back
+ // three times. Again it is unlikely that real code would have
+ // these calls sequentially, but instead buried in a more complex
+ // call structure. This is just for illustrative puproses.
+ xSemaphoreGiveRecursive( xSemaphore );
+ xSemaphoreGiveRecursive( xSemaphore );
+ xSemaphoreGiveRecursive( xSemaphore );
+
+ // Now the mutex can be taken by other tasks.
+ }
+ else
+ {
+ // We could not obtain the mutex and can therefore not access
+ // the shared resource safely.
+ }
+ }
+ }
+
+ * \defgroup xSemaphoreTakeRecursive xSemaphoreTakeRecursive
+ * \ingroup Semaphores
+ */
+#define xSemaphoreTakeRecursive( xMutex, xBlockTime ) xQueueTakeMutexRecursive( xMutex, xBlockTime )
+
+
/*
* xSemaphoreAltTake() is an alternative version of xSemaphoreTake().
*
@@ -174,14 +271,18 @@ typedef xQueueHandle xSemaphoreHandle;
* semphr. h
* xSemaphoreGive( xSemaphoreHandle xSemaphore )
*
- * Macro to release a semaphore. The semaphore must of been created using
- * vSemaphoreCreateBinary (), and obtained using sSemaphoreTake ().
+ * Macro to release a semaphore. The semaphore must have previously been
+ * created with a call to vSemaphoreCreateBinary(), xSemaphoreCreateMutex() or
+ * xSemaphoreCreateCounting(). and obtained using sSemaphoreTake().
*
- * This must not be used from an ISR. See xSemaphoreGiveFromISR () for
+ * This macro must not be used from an ISR. See xSemaphoreGiveFromISR () for
* an alternative which can be used from an ISR.
*
+ * This macro must also not be used on semaphores created using
+ * xSemaphoreCreateRecursiveMutex().
+ *
* @param xSemaphore A handle to the semaphore being released. This is the
- * handle returned by vSemaphoreCreateBinary ();
+ * handle returned when the semaphore was created.
*
* @return pdTRUE if the semaphore was released. pdFALSE if an error occurred.
* Semaphores are implemented using queues. An error can occur if there is
@@ -229,6 +330,90 @@ typedef xQueueHandle xSemaphoreHandle;
*/
#define xSemaphoreGive( xSemaphore ) xQueueGenericSend( ( xQueueHandle ) xSemaphore, NULL, semGIVE_BLOCK_TIME, queueSEND_TO_BACK )
+/**
+ * semphr. h
+ * xSemaphoreGiveRecursive( xSemaphoreHandle xSemaphore )
+ *
+ * Macro to recursively release, or 'give', a mutex type semaphore.
+ * The mutex must have previously been created using a call to
+ * xSemaphoreCreateRecursiveMutex();
+ *
+ * configUSE_RECURSIVE_MUTEXES must be set to 1 in FreeRTOSConfig.h for this
+ * macro to be available.
+ *
+ * This macro must not be used on mutexes created using xSemaphoreCreateMutex().
+ *
+ * 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 avilable to any other task until it has also 'given' the mutex back
+ * exactly five times.
+ *
+ * @param xMutex A handle to the mutex being released, or 'given'. This is the
+ * handle returned by xSemaphoreCreateMutex();
+ *
+ * @return pdTRUE if the semaphore was given.
+ *
+ * Example usage:
+
+ xSemaphoreHandle xMutex = NULL;
+
+ // A task that creates a mutex.
+ void vATask( void * pvParameters )
+ {
+ // Create the mutex to guard a shared resource.
+ xMutex = xSemaphoreCreateRecursiveMutex();
+ }
+
+ // A task that uses the mutex.
+ void vAnotherTask( void * pvParameters )
+ {
+ // ... Do other things.
+
+ if( xMutex != NULL )
+ {
+ // See if we can obtain the mutex. If the mutex is not available
+ // wait 10 ticks to see if it becomes free.
+ if( xSemaphoreTakeRecursive( xSemaphore, ( portTickType ) 10 ) == pdTRUE )
+ {
+ // We were able to obtain the mutex and can now access the
+ // shared resource.
+
+ // ...
+ // For some reason due to the nature of the code further calls to
+ // xSemaphoreTakeRecursive() are made on the same mutex. In real
+ // code these would not be just sequential calls as this would make
+ // no sense. Instead the calls are likely to be buried inside
+ // a more complex call structure.
+ xSemaphoreTakeRecursive( xSemaphore, ( portTickType ) 10 );
+ xSemaphoreTakeRecursive( xSemaphore, ( portTickType ) 10 );
+
+ // The mutex has now been 'taken' three times, so will not be
+ // available to another task until it has also been given back
+ // three times. Again it is unlikely that real code would have
+ // these calls sequentially, it would be more likely that the calls
+ // to xSemaphoreGiveRecursive() would be called as a call stack
+ // unwound. This is just for demonstrative purposes.
+ xSemaphoreGiveRecursive( xSemaphore );
+ xSemaphoreGiveRecursive( xSemaphore );
+ xSemaphoreGiveRecursive( xSemaphore );
+
+ // Now the mutex can be taken by other tasks.
+ }
+ else
+ {
+ // We could not obtain the mutex and can therefore not access
+ // the shared resource safely.
+ }
+ }
+ }
+
+ * \defgroup xSemaphoreGiveRecursive xSemaphoreGiveRecursive
+ * \ingroup Semaphores
+ */
+#define xSemaphoreGiveRecursive( xMutex ) xQueueGiveMutexRecursive( xMutex )
+
/*
* xSemaphoreAltGive() is an alternative version of xSemaphoreGive().
*
@@ -251,8 +436,8 @@ typedef xQueueHandle xSemaphoreHandle;
portSHORT sTaskPreviouslyWoken
)
*
- * Macro to release a semaphore. The semaphore must of been created using
- * vSemaphoreCreateBinary (), and obtained using xSemaphoreTake ().
+ * Macro to release a semaphore. The semaphore must have previously been
+ * created with a call to vSemaphoreCreateBinary() or xSemaphoreCreateCounting().
*
* Mutex type semaphores (those created using a call to xSemaphoreCreateMutex())
* must not be used with this macro.
@@ -260,7 +445,7 @@ typedef xQueueHandle xSemaphoreHandle;
* This macro can be used from an ISR.
*
* @param xSemaphore A handle to the semaphore being released. This is the
- * handle returned by vSemaphoreCreateBinary ();
+ * handle returned when the semaphore was created.
*
* @param sTaskPreviouslyWoken This is included so an ISR can make multiple calls
* to xSemaphoreGiveFromISR () from a single interrupt. The first call
@@ -283,8 +468,8 @@ typedef xQueueHandle xSemaphoreHandle;
{
for( ;; )
{
- // We want this task to run every 10 ticks or a timer. The semaphore
- // was created before this task was started
+ // We want this task to run every 10 ticks of a timer. The semaphore
+ // was created before this task was started.
// Block waiting for the semaphore to become available.
if( xSemaphoreTake( xSemaphore, LONG_TIME ) == pdTRUE )
@@ -295,7 +480,8 @@ typedef xQueueHandle xSemaphoreHandle;
// We have finished our task. Return to the top of the loop where
// we will block on the semaphore until it is time to execute
- // again.
+ // again. Note when using the semaphore for synchronisation with an
+ // ISR in this manner there is no need to 'give' the semaphore back.
}
}
}
@@ -316,11 +502,18 @@ typedef xQueueHandle xSemaphoreHandle;
if( ucLocalTickCount >= TICKS_TO_WAIT )
{
// Unblock the task by releasing the semaphore.
- xSemaphoreGiveFromISR( xSemaphore, xTaskWoken );
+ xTaskWoken = xSemaphoreGiveFromISR( xSemaphore, xTaskWoken );
// Reset the count so we release the semaphore again in 10 ticks time.
ucLocalTickCount = 0;
}
+
+ if( xTaskWoken != pdFALSE )
+ {
+ // We can force a context switch here. Context switching from an
+ // ISR uses port specific syntax. Check the demo task for your port
+ // to find the syntax required.
+ }
}
* \defgroup xSemaphoreGiveFromISR xSemaphoreGiveFromISR
@@ -335,6 +528,10 @@ typedef xQueueHandle xSemaphoreHandle;
* Macro that implements a mutex semaphore by using the existing queue
* mechanism.
*
+ * Mutexes created using this macro can be accessed using the xSemaphoreTake()
+ * and xSemaphoreGive() macros. The xSemaphoreTakeRecursive() and
+ * xSemaphoreGiveRecursive() macros should not be used.
+ *
* This type of semaphore uses a priority inheritance mechanism so a task
* 'taking' a semaphore MUST ALWAYS 'give' the semaphore back once the
* semaphore it is no longer required.
@@ -370,6 +567,60 @@ typedef xQueueHandle xSemaphoreHandle;
* \ingroup Semaphores
*/
#define xSemaphoreCreateMutex() xQueueCreateMutex()
+
+
+/**
+ * semphr. h
+ * xSemaphoreHandle xSemaphoreCreateRecursiveMutex( void )
+ *
+ * Macro that implements a recursive mutex by using the existing queue
+ * mechanism.
+ *
+ * Mutexes created using this macro can be accessed using the
+ * xSemaphoreTakeRecursive() and xSemaphoreGiveRecursive() macros. The
+ * xSemaphoreTake() and xSemaphoreGive() macros should not be used.
+ *
+ * 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 avilable to any other task until it has also 'given' the mutex back
+ * exactly five times.
+ *
+ * This type of semaphore uses a priority inheritance mechanism so a task
+ * 'taking' a semaphore MUST ALWAYS 'give' the semaphore back once the
+ * semaphore it is no longer required.
+ *
+ * Mutex type semaphores cannot be used from within interrupt service routines.
+ *
+ * See xSemaphoreCreateBinary() for an alternative implementation that can be
+ * used for pure synchronisation (where one task or interrupt always 'gives' the
+ * semaphore and another always 'takes' the semaphore) and from within interrupt
+ * service routines.
+ *
+ * @return xSemaphore Handle to the created mutex semaphore. Should be of type
+ * xSemaphoreHandle.
+ *
+ * Example usage:
+
+ xSemaphoreHandle xSemaphore;
+
+ void vATask( void * pvParameters )
+ {
+ // Semaphore cannot be used before a call to xSemaphoreCreateMutex().
+ // This is a macro so pass the variable in directly.
+ xSemaphore = xSemaphoreCreateRecursiveMutex();
+
+ if( xSemaphore != NULL )
+ {
+ // The semaphore was created successfully.
+ // The semaphore can now be used.
+ }
+ }
+
+ * \defgroup vSemaphoreCreateMutex vSemaphoreCreateMutex
+ * \ingroup Semaphores
+ */
#define xSemaphoreCreateRecursiveMutex() xQueueCreateMutex()
/**
@@ -435,8 +686,6 @@ typedef xQueueHandle xSemaphoreHandle;
*/
#define xSemaphoreCreateCounting( uxMaxCount, uxInitialCount ) xQueueCreateCountingSemaphore( uxMaxCount, uxInitialCount )
-#define xSemaphoreTakeRecursive( xMutex, xBlockTime ) xQueueTakeMutexRecursive( xMutex, xBlockTime )
-#define xSemaphoreGiveRecursive( xMutex ) xQueueGiveMutexRecursive( xMutex )
#endif /* SEMAPHORE_H */