ADA Thread Compilation

1
ADA Thread Compilation

• Montana State University
• CS 550 Design Translation of Programming
  Languages
• Shen Wan

2
Ada Task Syntax

• task_type_declaration task type
  Defining_Identifier known_discriminant_part
  is task_definitionsingle_task_declaration
  task defining_identifier is
  task_definitiontask_definition
  task_item private task_item end
  task_identifiertask_body task body
  defining_identifier is declarative_part
  begin handled_sequence_of_statements end
  task_identifier
• Ex http//www.infres.enst.fr/pautet/Ada95/e_c29_
  p1.ada

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Task Execution

• Activation -- the elaboration of the declarative
  part of the task body (local variables in the
  body of the task are created and initialized
  during activation). The Activator identifies the
  task which created and activated the task.

• Normal execution -- the execution of the
  statements visible within the body of the task.
• Finalization -- the execution of any finalization
  code associated with any objects in its
  declarative part.

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Ex GNU Ada Compiler

• http//www.gnat.com/
• Support Ada 95
• Multi-platform
• Based on GNU GCC compiler
• Open source

5
GNARL Implementation

• Each task has an associated Ada Task Control
  Block (ATCB).
• There is a list which contains all the ATCBs (All
  Tasks List).
• One auxiliary list is used to activate task
  objects in the same Ada scope at the same time.
• Masters define a task scope which allow the
  run-time to manage task finalization.
• The Ada task specification is translated by the
  compiler into a limited record
• The Ada task body is translated into a procedure
  with intermixed calls to the RTS to manage the
  task body creation, activation and finalization.
• The environment task is responsible for the RTS
  initialization. After this work, it also executes
  the main Ada subprogram.

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Run-Time Information Associated with Each Task
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Task Specification

• The Ada task type is translated by the compiler
  into a limited record with the same
  discriminants.
• For example, the following task specification
  task type T_Task (Discriminant DType) is
  ...end T_Task ...is translated by the compiler
  into the following code

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Translated Code

• T_TaskE aliased Boolean False --body
  elaboratedT_TaskZ Size_Type
  Unspecified_Size Size_Type (Size_Expression)
  --task stack sizetype T_TaskV (Discriminant
  DType) is limited record _Task_Id
  System.Tasking.Task_Id Entry_Family
  array (Bounds) of Void _Priority
  Integer Priority_Expression _Size
  Size_Type Size_Expression _Task_Info
  Task_Info_Type Task_Info_Expression
  _Task_Name Task_Image_Type new
  String'(Task_Name) end record

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Task Body

• the compiler translates the task body into a
  procedure.
• For example, the following task body task body
  T_Task is ltDeclarationsgtbegin
  ltStatementsgtend T_Task...is translated by the
  compiler into the following code

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Translated Code

• procedure T_TaskB (_Task access T_TaskV) is
  Discriminant Dtype renames _Task.Discriminant
  procedure _Clean is begin Abort_Defer
  GNARL.Complete_Task Abort_Undefer end
  _Cleanbegin Abort_Undefer ltDeclarationsgt
  Activate_Tasks GNARL.Complete_Activation
  ltStatementsgtat end _Cleanend T_TaskB

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References

• A Detailed Description of the GNU Ada Run Time,
  http//www.iuma.ulpgc.es/users/jmiranda/gnat-rts/i
  ndex.htm