RTEMS 4.9.5 On-Line Library

Barrier Manager Building a Barrier Attribute Set

RTEMS C User's Guide

20.2.2: Building a Barrier Attribute Set

In general, an attribute set is built by a bitwise OR of the desired attribute components. The following table lists the set of valid barrier attributes:

RTEMS_BARRIER_AUTOMATIC_RELEASE - automatically release the barrier when the configured number of tasks are blocked
RTEMS_BARRIER_MANUAL_RELEASE - only release the barrier when the application invokes the rtems_barrier_release directive. (default)

NOTE: Barriers only support FIFO blocking order because all waiting tasks are released as a set. Thus the released tasks will all become ready to execute at the same time and compete for the processor based upon their priority.

Attribute values are specifically designed to be mutually exclusive, therefore bitwise OR and addition operations are equivalent as long as each attribute appears exactly once in the component list. An attribute listed as a default is not required to appear in the attribute list, although it is a good programming practice to specify default attributes. If all defaults are desired, the attribute RTEMS_DEFAULT_ATTRIBUTES should be specified on this call.

This example demonstrates the attribute_set parameter needed to create a barrier with the automatic release policy. The attribute_set parameter passed to the rtems_barrier_create directive will be RTEMS_BARRIER_AUTOMATIC_RELEASE. In this case, the user must also specify the maximum_waiters parameter.

RTEMS C User's Guide