Semaphore Manager

The Semaphore Manager utilizes standard Dijkstra counting semaphores to provide synchronization and mutual exclusion capabilities. More...

Functions
rtems_status_code	rtems_semaphore_create (rtems_name name, uint32_t count, rtems_attribute attribute_set, rtems_task_priority priority_ceiling, rtems_id *id)
	Creates a semaphore.
rtems_status_code	rtems_semaphore_ident (rtems_name name, uint32_t node, rtems_id *id)
	Identifies a semaphore by the object name.
rtems_status_code	rtems_semaphore_delete (rtems_id id)
	Deletes the semaphore.
rtems_status_code	rtems_semaphore_obtain (rtems_id id, rtems_option option_set, rtems_interval timeout)
	Obtains the semaphore.
rtems_status_code	rtems_semaphore_release (rtems_id id)
	Releases the semaphore.
rtems_status_code	rtems_semaphore_flush (rtems_id id)
	Flushes the semaphore.
rtems_status_code	rtems_semaphore_set_priority (rtems_id semaphore_id, rtems_id scheduler_id, rtems_task_priority new_priority, rtems_task_priority *old_priority)
	Sets the priority by scheduler for the semaphore.

Detailed Description

The Semaphore Manager utilizes standard Dijkstra counting semaphores to provide synchronization and mutual exclusion capabilities.

Function Documentation

rtems_semaphore_create()

rtems_status_code rtems_semaphore_create	(	rtems_name	name,
		uint32_t	count,
		rtems_attribute	attribute_set,
		rtems_task_priority	priority_ceiling,
		rtems_id *	id
	)

Creates a semaphore.

Parameters

	name	is the object name of the semaphore.
	count	is the initial count of the semaphore. If the semaphore is a binary semaphore, then a count of 0 will make the calling task the owner of the binary semaphore and a count of 1 will create a binary semaphore without an owner.
	attribute_set	is the attribute set of the semaphore.
	priority_ceiling	is the priority ceiling if the semaphore is a binary semaphore with the priority ceiling or MrsP locking protocol as defined by the attribute set.
[out]	id	is the pointer to an rtems_id object. When the directive call is successful, the identifier of the created semaphore will be stored in this object.

This directive creates a semaphore which resides on the local node. The semaphore has the user-defined object name specified in name and the initial count specified in count. The assigned object identifier is returned in id. This identifier is used to access the semaphore with other semaphore related directives.

The attribute set specified in attribute_set is built through a bitwise or of the attribute constants described below. Not all combinations of attributes are allowed. Some attributes are mutually exclusive. If mutually exclusive attributes are combined, the behaviour is undefined. Attributes not mentioned below are not evaluated by this directive and have no effect. Default attributes can be selected by using the RTEMS_DEFAULT_ATTRIBUTES constant. The attribute set defines

• the scope of the semaphore: RTEMS_LOCAL (default) or RTEMS_GLOBAL,
• the task wait queue discipline used by the semaphore: RTEMS_FIFO (default) or RTEMS_PRIORITY,
• the class of the semaphore: RTEMS_COUNTING_SEMAPHORE (default), RTEMS_BINARY_SEMAPHORE, or RTEMS_SIMPLE_BINARY_SEMAPHORE, and
• the locking protocol of a binary semaphore: no locking protocol (default), RTEMS_INHERIT_PRIORITY, RTEMS_PRIORITY_CEILING, or RTEMS_MULTIPROCESSOR_RESOURCE_SHARING.

The semaphore has a local or global scope in a multiprocessing network (this attribute does not refer to SMP systems). The scope is selected by the mutually exclusive RTEMS_LOCAL and RTEMS_GLOBAL attributes.

• A local scope is the default and can be emphasized through the use of the RTEMS_LOCAL attribute. A local semaphore can be only used by the node which created it.
• A global scope is established if the RTEMS_GLOBAL attribute is set. Setting the global attribute in a single node system has no effect.

The task wait queue discipline is selected by the mutually exclusive RTEMS_FIFO and RTEMS_PRIORITY attributes.

• The FIFO discipline is the default and can be emphasized through use of the RTEMS_FIFO attribute.
• The priority discipline is selected by the RTEMS_PRIORITY attribute. The locking protocols require the priority discipline.

The semaphore class is selected by the mutually exclusive RTEMS_COUNTING_SEMAPHORE, RTEMS_BINARY_SEMAPHORE, and RTEMS_SIMPLE_BINARY_SEMAPHORE attributes.

• The counting semaphore class is the default and can be emphasized through use of the RTEMS_COUNTING_SEMAPHORE attribute.
• The binary semaphore class is selected by the RTEMS_BINARY_SEMAPHORE attribute. Binary semaphores are mutual exclusion (mutex) synchronization primitives which may have an owner. The count of a binary semaphore is restricted to 0 and 1 values.
• The simple binary semaphore class is selected by the RTEMS_SIMPLE_BINARY_SEMAPHORE attribute. Simple binary semaphores have no owner. They may be used for task and interrupt synchronization. The count of a simple binary semaphore is restricted to 0 and 1 values.

Binary semaphores may use a locking protocol. If a locking protocol is selected, then the scope shall be local and the priority task wait queue discipline shall be selected. The locking protocol is selected by the mutually exclusive RTEMS_INHERIT_PRIORITY, RTEMS_PRIORITY_CEILING, and RTEMS_MULTIPROCESSOR_RESOURCE_SHARING attributes.

• The default is no locking protocol. This can be emphasized through use of the RTEMS_NO_INHERIT_PRIORITY, RTEMS_NO_MULTIPROCESSOR_RESOURCE_SHARING, and RTEMS_NO_PRIORITY_CEILING attributes.
• The priority inheritance locking protocol is selected by the RTEMS_INHERIT_PRIORITY attribute.
• The priority ceiling locking protocol is selected by the RTEMS_PRIORITY_CEILING attribute. For this locking protocol a priority ceiling shall be specified in priority_ceiling.
• The MrsP locking protocol is selected by the RTEMS_MULTIPROCESSOR_RESOURCE_SHARING attribute in SMP configurations, otherwise this attribute selects the priority ceiling locking protocol. For these locking protocols a priority ceiling shall be specified in priority_ceiling. This priority is used to set the priority ceiling for all schedulers. This can be changed later with the rtems_semaphore_set_priority() directive using the returned object identifier.

Return values

RTEMS_SUCCESSFUL	The requested operation was successful.
RTEMS_INVALID_NAME	The name parameter was invalid.
RTEMS_INVALID_ADDRESS	The id parameter was NULL.
RTEMS_INVALID_NUMBER	The count parameter was invalid.
RTEMS_NOT_DEFINED	The attribute_set parameter was invalid.
RTEMS_TOO_MANY	There was no inactive object available to create a semaphore. The number of semaphores available to the application is configured through the CONFIGURE_MAXIMUM_SEMAPHORES application configuration option.
RTEMS_TOO_MANY	In multiprocessing configurations, there was no inactive global object available to create a global semaphore. The number of global objects available to the application is configured through the CONFIGURE_MP_MAXIMUM_GLOBAL_OBJECTS application configuration option.
RTEMS_INVALID_PRIORITY	The priority_ceiling parameter was invalid.

Notes

For control and maintenance of the semaphore, RTEMS allocates a SMCB from the local SMCB free pool and initializes it.

The SMCB for a global semaphore is allocated on the local node. Semaphores should not be made global unless remote tasks must interact with the semaphore. This is to avoid the system overhead incurred by the creation of a global semaphore. When a global semaphore is created, the semaphore's name and identifier must be transmitted to every node in the system for insertion in the local copy of the global object table.

Constraints

The following constraints apply to this directive:

• The directive may be called from within device driver initialization context.
• The directive may be called from within task context.
• The directive may obtain and release the object allocator mutex. This may cause the calling task to be preempted.
• When the directive operates on a global object, the directive sends a message to remote nodes. This may preempt the calling task.
• The number of semaphores available to the application is configured through the CONFIGURE_MAXIMUM_SEMAPHORES application configuration option.
• Where the object class corresponding to the directive is configured to use unlimited objects, the directive may allocate memory from the RTEMS Workspace.
• The number of global objects available to the application is configured through the CONFIGURE_MP_MAXIMUM_GLOBAL_OBJECTS application configuration option.

rtems_semaphore_delete()

rtems_status_code rtems_semaphore_delete

(

rtems_id

id

)

Deletes the semaphore.

Parameters

id	is the semaphore identifier.

This directive deletes the semaphore specified by id.

Return values

RTEMS_SUCCESSFUL	The requested operation was successful.
RTEMS_INVALID_ID	There was no semaphore associated with the identifier specified by id.
RTEMS_ILLEGAL_ON_REMOTE_OBJECT	The semaphore resided on a remote node.
RTEMS_RESOURCE_IN_USE	The binary semaphore had an owner.

Notes

Binary semaphores with an owner cannot be deleted.

When a semaphore is deleted, all tasks blocked waiting to obtain the semaphore will be readied and returned a status code which indicates that the semaphore was deleted.

The SMCB for the deleted semaphore is reclaimed by RTEMS.

When a global semaphore is deleted, the semaphore identifier must be transmitted to every node in the system for deletion from the local copy of the global object table.

The semaphore must reside on the local node, even if the semaphore was created with the RTEMS_GLOBAL attribute.

Proxies, used to represent remote tasks, are reclaimed when the semaphore is deleted.

Constraints

The following constraints apply to this directive:

• The directive may be called from within device driver initialization context.
• The directive may be called from within task context.
• The directive may obtain and release the object allocator mutex. This may cause the calling task to be preempted.
• When the directive operates on a global object, the directive sends a message to remote nodes. This may preempt the calling task.
• The calling task does not have to be the task that created the object. Any local task that knows the object identifier can delete the object.
• Where the object class corresponding to the directive is configured to use unlimited objects, the directive may free memory to the RTEMS Workspace.

rtems_semaphore_flush()

rtems_status_code rtems_semaphore_flush

(

rtems_id

id

)

Flushes the semaphore.

Parameters

id	is the semaphore identifier.

This directive unblocks all tasks waiting on the semaphore specified by id. The semaphore's count is not changed by this directive. Tasks which are unblocked as the result of this directive will return from the rtems_semaphore_obtain() directive with a status code of RTEMS_UNSATISFIED to indicate that the semaphore was not obtained.

Return values

RTEMS_SUCCESSFUL	The requested operation was successful.
RTEMS_INVALID_ID	There was no semaphore associated with the identifier specified by id.
RTEMS_ILLEGAL_ON_REMOTE_OBJECT	The semaphore resided on a remote node.
RTEMS_NOT_DEFINED	Flushing a semaphore using the MrsP locking protocol is undefined behaviour.

Notes

If the task to be unblocked resides on a different node from the semaphore, then the waiting task is unblocked, and the proxy used to represent the task is reclaimed.

It is not allowed to flush a local, binary semaphore using the MrsP locking protocol and any attempt to do this will just return the RTEMS_NOT_DEFINED status code. This error can only happen in SMP configurations.

For barrier synchronization, the Barrier Manager offers a cleaner alternative to using the semaphore flush directive. Unlike POSIX barriers, they have a manual release option.

Using the semaphore flush directive for condition synchronization in concert with another semaphore may be subject to the lost wake-up problem. The following attempt to implement a condition variable is broken.

#include <rtems.h>
#include <assert.h>
 
void cnd_wait( rtems_id cnd, rtems_id mtx )
{
  rtems_status_code sc;
 
  sc = rtems_semaphore_release( mtx );
  assert( sc == RTEMS_SUCCESSFUL );
 
  // Here, a higher priority task may run and satisfy the condition.
  // We may never wake up from the next semaphore obtain.
 
  sc = rtems_semaphore_obtain( cnd, RTEMS_WAIT, RTEMS_NO_TIMEOUT );
  assert( sc == RTEMS_UNSATISFIED );
 
  sc = rtems_semaphore_obtain( mtx, RTEMS_WAIT, RTEMS_NO_TIMEOUT );
  assert( sc == RTEMS_SUCCESSFUL );
}
 
void cnd_broadcast( rtems_id cnd )
{
  rtems_status_code sc;
 
  sc = rtems_semaphore_flush( cnd );
  assert( sc == RTEMS_SUCCESSFUL );
}

Constraints

The following constraints apply to this directive:

• When a local, counting semaphore or a local, simple binary semaphore is accessed, the directive may be called from within interrupt context.
• When a local semaphore is accessed, the directive may be called from within device driver initialization context.
• The directive may be called from within task context.
• The directive may unblock a task. This may cause the calling task to be preempted.
• When the directive operates on a remote object, the directive sends a message to the remote node and waits for a reply. This will preempt the calling task.

rtems_semaphore_ident()

rtems_status_code rtems_semaphore_ident	(	rtems_name	name,
		uint32_t	node,
		rtems_id *	id
	)

Identifies a semaphore by the object name.

Parameters

	name	is the object name to look up.
	node	is the node or node set to search for a matching object.
[out]	id	is the pointer to an rtems_id object. When the directive call is successful, the object identifier of an object with the specified name will be stored in this object.

This directive obtains a semaphore identifier associated with the semaphore name specified in name.

The node to search is specified in node. It shall be

• a valid node number,
• the constant RTEMS_SEARCH_ALL_NODES to search in all nodes,
• the constant RTEMS_SEARCH_LOCAL_NODE to search in the local node only, or
• the constant RTEMS_SEARCH_OTHER_NODES to search in all nodes except the local node.

Return values

RTEMS_SUCCESSFUL	The requested operation was successful.
RTEMS_INVALID_ADDRESS	The id parameter was NULL.
RTEMS_INVALID_NAME	The name parameter was 0.
RTEMS_INVALID_NAME	There was no object with the specified name on the specified nodes.
RTEMS_INVALID_NODE	In multiprocessing configurations, the specified node was invalid.

Notes

If the semaphore name is not unique, then the semaphore identifier will match the first semaphore with that name in the search order. However, this semaphore identifier is not guaranteed to correspond to the desired semaphore.

The objects are searched from lowest to the highest index. If node is RTEMS_SEARCH_ALL_NODES, all nodes are searched with the local node being searched first. All other nodes are searched from lowest to the highest node number.

If node is a valid node number which does not represent the local node, then only the semaphores exported by the designated node are searched.

This directive does not generate activity on remote nodes. It accesses only the local copy of the global object table.

The semaphore identifier is used with other semaphore related directives to access the semaphore.

Constraints

The following constraints apply to this directive:

• The directive may be called from within any runtime context.
• The directive will not cause the calling task to be preempted.

rtems_semaphore_obtain()

rtems_status_code rtems_semaphore_obtain	(	rtems_id	id,
		rtems_option	option_set,
		rtems_interval	timeout
	)

Obtains the semaphore.

Parameters

id	is the semaphore identifier.
option_set	is the option set.
timeout	is the timeout in clock ticks if the RTEMS_WAIT option is set. Use RTEMS_NO_TIMEOUT to wait potentially forever.

This directive obtains the semaphore specified by id.

The option set specified in option_set is built through a bitwise or of the option constants described below. Not all combinations of options are allowed. Some options are mutually exclusive. If mutually exclusive options are combined, the behaviour is undefined. Options not mentioned below are not evaluated by this directive and have no effect. Default options can be selected by using the RTEMS_DEFAULT_OPTIONS constant.

The calling task can wait or try to obtain the semaphore according to the mutually exclusive RTEMS_WAIT and RTEMS_NO_WAIT options.

• Waiting to obtain the semaphore is the default and can be emphasized through the use of the RTEMS_WAIT option. The timeout parameter defines how long the calling task is willing to wait. Use RTEMS_NO_TIMEOUT to wait potentially forever, otherwise set a timeout interval in clock ticks.
• Trying to obtain the semaphore is selected by the RTEMS_NO_WAIT option. If this option is defined, then the timeout parameter is ignored. When the semaphore cannot be immediately obtained, then the RTEMS_UNSATISFIED status is returned.

With either RTEMS_WAIT or RTEMS_NO_WAIT if the current semaphore count is positive, then it is decremented by one and the semaphore is successfully obtained by returning immediately with the RTEMS_SUCCESSFUL status code.

If the calling task chooses to return immediately and the current semaphore count is zero, then the RTEMS_UNSATISFIED status code is returned indicating that the semaphore is not available.

If the calling task chooses to wait for a semaphore and the current semaphore count is zero, then the calling task is placed on the semaphore's wait queue and blocked. If a local, binary semaphore was created with the RTEMS_INHERIT_PRIORITY attribute, then the priority of the task currently holding the binary semaphore will inherit the current priority set of the blocking task. The priority inheritance is carried out recursively. This means, that if the task currently holding the binary semaphore is blocked on another local, binary semaphore using the priority inheritance locking protocol, then the owner of this semaphore will inherit the current priority sets of both tasks, and so on. A task has a current priority for each scheduler.

Return values

RTEMS_SUCCESSFUL	The requested operation was successful.
RTEMS_INVALID_ID	There was no semaphore associated with the identifier specified by id.
RTEMS_NOT_DEFINED	The semaphore uses a priority ceiling and there was no priority ceiling defined for the home scheduler of the calling task.
RTEMS_UNSATISFIED	The semaphore could not be obtained immediately.
RTEMS_INVALID_PRIORITY	The semaphore uses a priority ceiling and the calling task had a current priority less than the priority ceiling.
RTEMS_INCORRECT_STATE	Acquiring of the local, binary semaphore by the calling task would have cased a deadlock.
RTEMS_INCORRECT_STATE	The calling task attempted to recursively obtain a local, binary semaphore using the MrsP locking protocol.
RTEMS_UNSATISFIED	The semaphore was flushed while the calling task was waiting to obtain the semaphore.
RTEMS_TIMEOUT	The timeout happened while the calling task was waiting to obtain the semaphore.
RTEMS_OBJECT_WAS_DELETED	The semaphore was deleted while the calling task was waiting to obtain the semaphore.

Notes

If a local, binary semaphore was created with the RTEMS_PRIORITY_CEILING or RTEMS_MULTIPROCESSOR_RESOURCE_SHARING attribute, a task successfully obtains the semaphore, and the priority of that task is greater than the ceiling priority for this semaphore, then the priority of the task acquiring the semaphore is elevated to that of the ceiling.

Deadlock situations are detected for local, binary semaphores. If a deadlock is detected, then the directive immediately returns the RTEMS_INCORRECT_STATE status code.

It is not allowed to recursively obtain (nested access) a local, binary semaphore using the MrsP locking protocol and any attempt to do this will just return the RTEMS_INCORRECT_STATE status code. This error can only happen in SMP configurations.

If the semaphore was created with the RTEMS_PRIORITY attribute, then the calling task is inserted into the wait queue according to its priority. However, if the semaphore was created with the RTEMS_FIFO attribute, then the calling task is placed at the rear of the wait queue.

Attempting to obtain a global semaphore which does not reside on the local node will generate a request to the remote node to access the semaphore. If the semaphore is not available and RTEMS_NO_WAIT was not specified, then the task must be blocked until the semaphore is released. A proxy is allocated on the remote node to represent the task until the semaphore is released.

Constraints

The following constraints apply to this directive:

• When a local, counting semaphore or a local, simple binary semaphore is accessed and the RTEMS_NO_WAIT option is set, the directive may be called from within interrupt context.
• When a local semaphore is accessed and the request can be immediately satisfied, the directive may be called from within device driver initialization context.
• The directive may be called from within task context.
• When the request cannot be immediately satisfied and the RTEMS_WAIT option is set, the calling task blocks at some point during the directive call.
• The timeout functionality of the directive requires a clock tick.
• When the directive operates on a remote object, the directive sends a message to the remote node and waits for a reply. This will preempt the calling task.

rtems_semaphore_release()

rtems_status_code rtems_semaphore_release

(

rtems_id

id

)

Releases the semaphore.

Parameters

id	is the semaphore identifier.

This directive releases the semaphore specified by id. If the semaphore's wait queue is not empty, then

• the first task on the wait queue is removed and unblocked, the semaphore's count is not changed, otherwise
• the semaphore's count is incremented by one for counting semaphores and set to one for binary and simple binary semaphores.

Return values

RTEMS_SUCCESSFUL	The requested operation was successful.
RTEMS_INVALID_ID	There was no semaphore associated with the identifier specified by id.
RTEMS_NOT_OWNER_OF_RESOURCE	The calling task was not the owner of the semaphore.
RTEMS_UNSATISFIED	The semaphore's count already had the maximum value of UINT32_MAX.

Notes

The calling task may be preempted if it causes a higher priority task to be made ready for execution.

The outermost release of a local, binary semaphore using the priority inheritance, priority ceiling, or MrsP locking protocol may result in the calling task having its priority lowered. This will occur if the highest priority of the calling task was available due to the ownership of the released semaphore. If a task was on the semaphore's wait queue, then the priority associated with the semaphore will be transferred to the new owner.

Releasing a global semaphore which does not reside on the local node will generate a request telling the remote node to release the semaphore.

If the task to be unblocked resides on a different node from the semaphore, then the semaphore allocation is forwarded to the appropriate node, the waiting task is unblocked, and the proxy used to represent the task is reclaimed.

Constraints

The following constraints apply to this directive:

• When a local, counting semaphore or a local, simple binary semaphore is accessed, the directive may be called from within interrupt context.
• When a local semaphore is accessed, the directive may be called from within device driver initialization context.
• The directive may be called from within task context.
• The directive may unblock a task. This may cause the calling task to be preempted.
• When the directive operates on a remote object, the directive sends a message to the remote node and waits for a reply. This will preempt the calling task.

rtems_semaphore_set_priority()

rtems_status_code rtems_semaphore_set_priority	(	rtems_id	semaphore_id,
		rtems_id	scheduler_id,
		rtems_task_priority	new_priority,
		rtems_task_priority *	old_priority
	)

Sets the priority by scheduler for the semaphore.

Parameters

	semaphore_id	is the semaphore identifier.
	scheduler_id	is the identifier of the scheduler corresponding to the new priority.
	new_priority	is the new priority corresponding to the specified scheduler.
[out]	old_priority	is the pointer to an rtems_task_priority object. When the directive call is successful, the old priority of the semaphore corresponding to the specified scheduler will be stored in this object.

This directive sets the priority of the semaphore specified by semaphore_id. The priority corresponds to the scheduler specified by scheduler_id.

The special priority value RTEMS_CURRENT_PRIORITY can be used to get the current priority without changing it.

The availability and use of a priority depends on the class and locking protocol of the semaphore:

• For local, binary semaphores using the MrsP locking protocol, the ceiling priority for each scheduler can be set by this directive.
• For local, binary semaphores using the priority ceiling protocol, the ceiling priority can be set by this directive.
• For other semaphore classes and locking protocols, setting a priority is undefined behaviour.

Return values

RTEMS_SUCCESSFUL	The requested operation was successful.
RTEMS_INVALID_ADDRESS	The old_priority parameter was NULL.
RTEMS_INVALID_ID	There was no scheduler associated with the identifier specified by scheduler_id.
RTEMS_INVALID_ID	There was no semaphore associated with the identifier specified by semaphore_id.
RTEMS_ILLEGAL_ON_REMOTE_OBJECT	The semaphore resided on a remote node.
RTEMS_INVALID_PRIORITY	The new_priority parameter was invalid.
RTEMS_NOT_DEFINED	Setting a priority for the class or locking protocol of the semaphore is undefined behaviour.

Notes

Please have a look at the following example:

#include <assert.h>
#include <rtems.h>
 
#define SCHED_A rtems_build_name( ' ', ' ', ' ', 'A' )
#define SCHED_B rtems_build_name( ' ', ' ', ' ', 'B' )
 
static void Init( rtems_task_argument arg )
{
  rtems_status_code   sc;
  rtems_id            semaphore_id;
  rtems_id            scheduler_a_id;
  rtems_id            scheduler_b_id;
  rtems_task_priority prio;
 
  (void) arg;
 
  // Get the scheduler identifiers
  sc = rtems_scheduler_ident( SCHED_A, &scheduler_a_id );
  assert( sc == RTEMS_SUCCESSFUL );
  sc = rtems_scheduler_ident( SCHED_B, &scheduler_b_id );
  assert( sc == RTEMS_SUCCESSFUL );
 
  // Create a local, binary semaphore using the MrsP locking protocol
  sc = rtems_semaphore_create(
    rtems_build_name( 'M', 'R', 'S', 'P' ),
    1,
    RTEMS_BINARY_SEMAPHORE | RTEMS_PRIORITY |
      RTEMS_MULTIPROCESSOR_RESOURCE_SHARING,
    1,
    &semaphore_id
  );
  assert( sc == RTEMS_SUCCESSFUL );
 
  // The ceiling priority for each scheduler is equal to the priority
  // specified for the semaphore creation.
  prio = RTEMS_CURRENT_PRIORITY;
  sc = rtems_semaphore_set_priority( semaphore_id, scheduler_a_id, prio, &prio );
  assert( sc == RTEMS_SUCCESSFUL );
  assert( prio == 1 );
 
  // Check the old value and set a new ceiling priority for scheduler B
  prio = 2;
  sc = rtems_semaphore_set_priority( semaphore_id, scheduler_b_id, prio, &prio );
  assert( sc == RTEMS_SUCCESSFUL );
  assert( prio == 1 );
 
  // Check the ceiling priority values
  prio = RTEMS_CURRENT_PRIORITY;
  sc = rtems_semaphore_set_priority( semaphore_id, scheduler_a_id, prio, &prio );
  assert( sc == RTEMS_SUCCESSFUL );
  assert( prio == 1 );
  prio = RTEMS_CURRENT_PRIORITY;
  sc = rtems_semaphore_set_priority( semaphore_id, scheduler_b_id, prio, &prio );
  assert( sc == RTEMS_SUCCESSFUL );
  assert( prio == 2 );
 
  sc = rtems_semaphore_delete( semaphore_id );
  assert( sc == RTEMS_SUCCESSFUL );
 
  rtems_shutdown_executive( 0 );
}
 
#define CONFIGURE_APPLICATION_NEEDS_CLOCK_DRIVER
#define CONFIGURE_APPLICATION_NEEDS_CONSOLE_DRIVER
#define CONFIGURE_MAXIMUM_TASKS 1
#define CONFIGURE_MAXIMUM_SEMAPHORES 1
#define CONFIGURE_MAXIMUM_PROCESSORS 2
 
#define CONFIGURE_SCHEDULER_SIMPLE_SMP
 
#include <rtems/scheduler.h>
 
RTEMS_SCHEDULER_CONTEXT_SIMPLE_SMP( a );
RTEMS_SCHEDULER_CONTEXT_SIMPLE_SMP( b );
 
#define CONFIGURE_SCHEDULER_TABLE_ENTRIES \
    RTEMS_SCHEDULER_TABLE_SIMPLE_SMP( a, SCHED_A ), \
    RTEMS_SCHEDULER_TABLE_SIMPLE_SMP( b, SCHED_B )
 
#define CONFIGURE_SCHEDULER_ASSIGNMENTS \
    RTEMS_SCHEDULER_ASSIGN( 0, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_MANDATORY ), \
    RTEMS_SCHEDULER_ASSIGN( 1, RTEMS_SCHEDULER_ASSIGN_PROCESSOR_MANDATORY )
 
#define CONFIGURE_RTEMS_INIT_TASKS_TABLE
#define CONFIGURE_INIT
 
#include <rtems/confdefs.h>

Constraints

The following constraints apply to this directive:

• The directive may be called from within interrupt context.
• The directive may be called from within device driver initialization context.
• The directive may be called from within task context.
• The directive may change the priority of a task. This may cause the calling task to be preempted.