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Richard Barry 17 years ago
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7
Demo/Common/Minimal/recmutex.c
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@ -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:

289
Source/include/semphr.h
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@ -99,18 +99,21 @@ typedef xQueueHandle xSemaphoreHandle;
* portTickType xBlockTime
* )</pre>
*
* <i>Macro</i> to obtain a semaphore. The semaphore must of been created using
* vSemaphoreCreateBinary ().
* <i>Macro</i> 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:
<pre>
@ -156,6 +159,100 @@ typedef xQueueHandle xSemaphoreHandle;
*/
#define xSemaphoreTake( xSemaphore, xBlockTime ) xQueueGenericReceive( ( xQueueHandle ) xSemaphore, NULL, xBlockTime, pdFALSE )
/**
* semphr. h
* xSemaphoreTakeRecursive(
* xSemaphoreHandle xMutex,
* portTickType xBlockTime
* )
*
* <i>Macro</i> 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:
<pre>
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.
}
}
}
</pre>
* \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
* <pre>xSemaphoreGive( xSemaphoreHandle xSemaphore )</pre>
*
* <i>Macro</i> to release a semaphore. The semaphore must of been created using
* vSemaphoreCreateBinary (), and obtained using sSemaphoreTake ().
* <i>Macro</i> 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
* <pre>xSemaphoreGiveRecursive( xSemaphoreHandle xSemaphore )</pre>
*
* <i>Macro</i> 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:
<pre>
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.
}
}
}
</pre>
* \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
)</pre>
*
* <i>Macro</i> to release a semaphore. The semaphore must of been created using
* vSemaphoreCreateBinary (), and obtained using xSemaphoreTake ().
* <i>Macro</i> 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.
}
}
</pre>
* \defgroup xSemaphoreGiveFromISR xSemaphoreGiveFromISR
@ -335,6 +528,10 @@ typedef xQueueHandle xSemaphoreHandle;
* <i>Macro</i> 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
* <pre>xSemaphoreHandle xSemaphoreCreateRecursiveMutex( void )</pre>
*
* <i>Macro</i> 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:
<pre>
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.
}
}
</pre>
* \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 */

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