vSemaphoreCreateBinary( xSemaphoreHandle xSemaphore )
Macro that creates a semaphore by using the existing queue mechanism. The queue length is 1 as this is a binary semaphore. The data size is 0 as we don't want to actually store any data - we just want to know if the queue is empty or full.
Binary semaphores and mutexes are very similar but have some subtle differences: Mutexes include
a priority inheritance mechanism, binary semaphores do not. This makes binary semaphores the better choice for implementing
synchronisation (between tasks or between tasks and an interrupt), and mutexes the better choice for implementing simple
A binary semaphore need not be given back once
obtained, so task synchronisation can be implemented by one task/interrupt continuously
'giving' the semaphore while another continuously 'takes' the semaphore. This is demonstrated by
the sample code on the xSemaphoreGiveFromISR() documentation page.
The priority of a task that 'takes' a mutex can potentially be raised if another task of higher
priority attempts to obtain the same mutex. The task that owns the mutex 'inherits' the priority
of the task attempting to 'take' the same mutex. This means the mutex must always be 'given' back -
otherwise the higher priority task will never be able to obtain the mutex, and the lower priority
task will never 'disinherit' the priority. An example of a mutex being used to implement mutual
exclusion is provided on the xSemaphoreTake() documentation page.
Both mutex and binary semaphores are assigned to variables of type xSemaphoreHandle and can be used
in any API function that takes a parameter of this type.
void vATask( void * pvParameters )
// Semaphore cannot be used before a call to vSemaphoreCreateBinary ().
// This is a macro so pass the variable in directly.
vSemaphoreCreateBinary( xSemaphore );
if( xSemaphore != NULL )
// The semaphore was created successfully.
// The semaphore can now be used.
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