2.144 Pragma Profile

Syntax:

pragma Profile (Ravenscar | Restricted | Rational |
                GNAT_Extended_Ravenscar | GNAT_Ravenscar_EDF );

This pragma is standard in Ada 2005, but is available in all earlier versions of Ada as an implementation-defined pragma. This is a configuration pragma that establishes a set of configuration pragmas that depend on the argument. Ravenscar is standard in Ada 2005. The other possibilities (Restricted, Rational, GNAT_Extended_Ravenscar, GNAT_Ravenscar_EDF) are implementation-defined. The set of configuration pragmas is defined in the following sections.

• * Pragma Profile (Ravenscar)

  The Ravenscar profile is standard in Ada 2005, but is available in all earlier versions of Ada as an implementation-defined pragma. This profile establishes the following set of configuration pragmas:

  • * Task_Dispatching_Policy (FIFO_Within_Priorities)

    [RM D.2.2] Tasks are dispatched following a preemptive priority-ordered scheduling policy.

  • * Locking_Policy (Ceiling_Locking)

    [RM D.3] While tasks and interrupts execute a protected action, they inherit the ceiling priority of the corresponding protected object.

  • * Detect_Blocking

    This pragma forces the detection of potentially blocking operations within a protected operation, and to raise Program_Error if that happens.

  plus the following set of restrictions:

  • * Max_Entry_Queue_Length => 1

    No task can be queued on a protected entry.

  • * Max_Protected_Entries => 1
  • * Max_Task_Entries => 0

    No rendezvous statements are allowed.

  • * No_Abort_Statements
  • * No_Dynamic_Attachment
  • * 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

  The Ravenscar profile also includes the following restrictions that specify that there are no semantic dependences on the corresponding predefined packages:

  • * No_Dependence => Ada.Asynchronous_Task_Control
  • * No_Dependence => Ada.Calendar
  • * No_Dependence => Ada.Execution_Time.Group_Budget
  • * No_Dependence => Ada.Execution_Time.Timers
  • * No_Dependence => Ada.Task_Attributes
  • * No_Dependence => System.Multiprocessors.Dispatching_Domains

  This set of configuration pragmas and restrictions correspond to the definition of the ’Ravenscar Profile’ for limited tasking, devised and published by the International Real-Time Ada Workshop, 1997. A description is also available at ‘http://www-users.cs.york.ac.uk/~burns/ravenscar.ps’.

  The original definition of the profile was revised at subsequent IRTAW meetings. It has been included in the ISO Guide for the Use of the Ada Programming Language in High Integrity Systems, and was made part of the Ada 2005 standard. The formal definition given by the Ada Rapporteur Group (ARG) can be found in two Ada Issues (AI-249 and AI-305) available at ‘http://www.ada-auth.org/cgi-bin/cvsweb.cgi/ais/ai-00249.txt’ and ‘http://www.ada-auth.org/cgi-bin/cvsweb.cgi/ais/ai-00305.txt’.

  The above set is a superset of the restrictions provided by pragma Profile (Restricted), it includes six additional restrictions (Simple_Barriers, No_Select_Statements, No_Calendar, No_Implicit_Heap_Allocations, No_Relative_Delay and No_Task_Termination). This means that pragma Profile (Ravenscar), like the pragma Profile (Restricted), automatically causes the use of a simplified, more efficient version of the tasking run-time library.

• * Pragma Profile (GNAT_Extended_Ravenscar)

  This profile corresponds to a GNAT specific extension of the Ravenscar profile. The profile may change in the future although only in a compatible way: some restrictions may be removed or relaxed. It is defined as a variation of the Ravenscar profile.

  The No_Implicit_Heap_Allocations restriction has been replaced by No_Implicit_Task_Allocations and No_Implicit_Protected_Object_Allocations.

  The Simple_Barriers restriction has been replaced by Pure_Barriers.

  The Max_Protected_Entries, Max_Entry_Queue_Length, and No_Relative_Delay restrictions have been removed.

• * Pragma Profile (GNAT_Ravenscar_EDF)

  This profile corresponds to the Ravenscar profile but using EDF_Across_Priority as the Task_Scheduling_Policy.

• * Pragma Profile (Restricted)

  This profile corresponds to the GNAT restricted run time. It establishes the following set of restrictions:

  • * No_Abort_Statements
  • * No_Entry_Queue
  • * No_Task_Hierarchy
  • * No_Task_Allocators
  • * No_Dynamic_Priorities
  • * No_Terminate_Alternatives
  • * No_Dynamic_Attachment
  • * No_Protected_Type_Allocators
  • * No_Local_Protected_Objects
  • * No_Requeue_Statements
  • * No_Task_Attributes_Package
  • * Max_Asynchronous_Select_Nesting = 0
  • * Max_Task_Entries = 0
  • * Max_Protected_Entries = 1
  • * Max_Select_Alternatives = 0

  This set of restrictions causes the automatic selection of a simplified version of the run time that provides improved performance for the limited set of tasking functionality permitted by this set of restrictions.

• * Pragma Profile (Rational)

  The Rational profile is intended to facilitate porting legacy code that compiles with the Rational APEX compiler, even when the code includes non- conforming Ada constructs. The profile enables the following three pragmas:

  • * pragma Implicit_Packing
  • * pragma Overriding_Renamings
  • * pragma Use_VADS_Size