D.13 The Ravenscar Profile
Legality Rules
Static Semantics
{
AI95-00249-01}
{
AI95-00297-01}
{
AI95-00394-01}
{
AI05-0171-1}
{
AI05-0246-1}
{
AI12-0055-1}
{
AI12-0073-1}
pragma Task_Dispatching_Policy (FIFO_Within_Priorities);
pragma Locking_Policy (Ceiling_Locking);
pragma Detect_Blocking;
pragma Restrictions (
No_Abort_Statements,
No_Dynamic_Attachment,
No_Dynamic_CPU_Assignment,
No_Dynamic_Priorities,
No_Implicit_Heap_Allocations,
No_Local_Protected_Objects,
No_Local_Timing_Events,
No_Protected_Type_Allocators,
No_Relative_Delay,
No_Requeue_Statements,
No_Select_Statements,
No_Specific_Termination_Handlers,
No_Task_Allocators,
No_Task_Hierarchy,
No_Task_Termination,
Simple_Barriers,
Max_Entry_Queue_Length => 1,
Max_Protected_Entries => 1,
Max_Task_Entries => 0,
No_Dependence => Ada.Asynchronous_Task_Control,
No_Dependence => Ada.Calendar,
No_Dependence => Ada.Execution_Time.Group_Budgets,
No_Dependence => Ada.Execution_Time.Timers,
No_Dependence => Ada.Synchronous_Barriers,
No_Dependence => Ada.Task_Attributes,
No_Dependence => System.Multiprocessors.Dispatching_Domains);
Discussion: The Ravenscar profile is
named for the location of the meeting that defined its initial version.
The name is now in widespread use, so we stick with existing practice,
rather than using a more descriptive name.
Paragraph 7 was deleted.
Implementation Requirements
Implementation Advice
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AI05-0171-1}
On a multiprocessor system, an implementation should support a fully
partitioned approach. Each processor should have separate and disjoint
ready queues.
Implementation Advice: On a multiprocessor
system, each processor should have a separate and disjoint ready queue.
42 {
AI95-00249-01}
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AI05-0246-1}
The effect of the Max_Entry_Queue_Length => 1 restriction applies
only to protected entry queues due to the accompanying restriction of
Max_Task_Entries => 0.
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AI12-0055-1}
When the Ravenscar profile is in effect (via the effect of the No_Dynamic_CPU_Assignment
restriction), all of the tasks in the partition will execute on a single
CPU unless the programmer explicitly uses aspect CPU to specify the CPU
assignments for tasks. The use of multiple CPUs requires care, as many
guarantees of single CPU scheduling no longer apply.
44 {
AI12-0055-1}
It is not recommended to specify the CPU of a task to be Not_A_Specific_CPU
when the Ravenscar profile is in effect. How a partition executes strongly
depends on the assignment of tasks to CPUs.
Extensions to Ada 95
Wording Changes from Ada 2005
{
AI05-0171-1}
How Ravenscar behaves on a multiprocessor system is now defined.
Incompatibilities With Ada 2012
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AI05-0073-1}
Corrigendum: The Ravenscar profile no longer
allows the use of package Synchronous_Barriers, as this package violates
the fundamental Ravenscar requirement that each waiting point can only
block (and release) a single task. This is incompatible with the published
Ada 2012 standard, but it is unlikely that any existing Ravenscar runtime
ever usefully supported barriers.
{
AI05-0055-1}
Corrigendum:The Ravenscar profile (via the effect of the new restriction
No_Dynamic_CPU_Assignment) no longer allows setting the CPU aspect of
a task to a non-static value. While this was allowed, an implementation
would have had to come up with a creative interpretation of the Ada 2012
requirement to define the association of tasks to processors statically.
As such, the new check is more likely to catch bugs than break a working
program.
Ada 2005 and 2012 Editions sponsored in part by Ada-Europe
