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Text File | 1995-10-17 | 27.8 KB | 697 lines

------------------------------------------------------------------------------ -- -- -- GNU ADA RUNTIME LIBRARY (GNARL) COMPONENTS -- -- -- -- S Y S T E M . T A S K I N G -- -- -- -- S p e c -- -- -- -- $Revision: 1.27 $ -- -- -- -- Copyright (c) 1991,1992,1993,1994,1995 FSU, All Rights Reserved -- -- -- -- GNARL is free software; you can redistribute it and/or modify it under -- -- terms of the GNU Library General Public License as published by the -- -- Free Software Foundation; either version 2, or (at your option) any -- -- later version. GNARL is distributed in the hope that it will be use- -- -- ful, but but WITHOUT ANY WARRANTY; without even the implied warranty of -- -- MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Gen- -- -- eral Library Public License for more details. You should have received -- -- a copy of the GNU Library General Public License along with GNARL; see -- -- file COPYING.LIB. If not, write to the Free Software Foundation, 675 -- -- Mass Ave, Cambridge, MA 02139, USA. -- -- -- ------------------------------------------------------------------------------ -- This package provides necessary type definitions for compiler interface. with Ada.Finalization; with System.Task_Primitives; -- Used for, Task_Primitives.Lock with System.Compiler_Exceptions; -- Used for, Exception_ID package System.Tasking is --------------------------------- -- Task_ID related definitions -- --------------------------------- type Ada_Task_Control_Block; type Task_ID is access Ada_Task_Control_Block; -- This should be a private type. However, compiler generates internal -- while compiling s-taprob.adb Null_Task : constant Task_ID; type Task_List is array (Positive range <>) of Task_ID; function Self return Task_ID; pragma Inline (Self); ----------------------------------- -- Master_ID related definitions -- ----------------------------------- type Master_ID is private; ---------------------------------------------- -- Task size, interrupt info, priority info -- ---------------------------------------------- type Task_Storage_Size is new integer; type Interrupt_ID is range 0 .. 31; type Size_Type is new Task_Storage_Size; Unspecified_Size : constant Size_Type := Size_Type'First; Unspecified_Priority : constant Integer := System.Priority'First - 1; Priority_Not_Boosted : constant Integer := System.Priority'First - 1; subtype Rendezvous_Priority is Integer range Priority_Not_Boosted .. System.Priority'Last; ----------------------- -- Enumeration types -- ----------------------- type Task_Stage is ( Created, -- Task has been created but has not begun activation. Can_Activate, -- Task has begin activation. Active, -- Task has completed activation and is executing the task body. Await_Dependents, -- Task is trying to complete a task master other than itself, -- and is waiting for the tasks dependent on that master to become -- passive (be complete, terminated, or be waiting on a terminate -- alternative). Passive, -- The task is passive. Completing, -- The task is committed to becoming complete, but has not yet -- satisfied all of the conditions for completion. This -- acts as a claim to completion; once Stage is set to this value, -- no other task can continue with completion. Complete, -- The task is complete. The task and all of its dependents are -- passive; some dependents may still be waiting on terminate -- alternatives. Terminated); -- The task is terminated. All dependents waiting on terminate -- alternatives have been awakened and have terminated themselves. type Accepting_State is ( Not_Accepting, -- task is not ready to accept any entry call Trivial_Accept, -- "accept E;" Simple_Accept, -- "accept E do ... end E;" Select_Wait); -- most general case type Call_Modes is (Simple_Call, Conditional_Call, Asynchronous_Call); type Select_Modes is (Simple_Mode, Else_Mode, Terminate_Mode); ----------------------------------- -- ATC_Level related definitions -- ----------------------------------- Max_ATC_Nesting : constant Natural := 20; subtype ATC_Level_Base is Integer range 0 .. Max_ATC_Nesting; ATC_Level_Infinity : constant ATC_Level_Base := ATC_Level_Base'Last; subtype ATC_Level is ATC_Level_Base range ATC_Level_Base'First .. ATC_Level_Base'Last - 1; subtype ATC_Level_Index is ATC_Level range ATC_Level'First + 1 .. ATC_Level'Last; ------------------------------- -- Entry related definitions -- ------------------------------- Null_Entry : constant := 0; Max_Entry : constant := Integer'Last; Interrupt_Entry : constant := -2; Cancelled_Entry : constant := -1; type Entry_Index is range Interrupt_Entry .. Max_Entry; type Entry_Call_Record; type Entry_Call_Link is access all Entry_Call_Record; type Entry_Queue is record Head : Entry_Call_Link; Tail : Entry_Call_Link; end record; ---------------------------- -- PO related definitions -- ---------------------------- Null_Protected_Entry : constant := Null_Entry; Max_Protected_Entry : constant := Max_Entry; type Protected_Entry_Index is new Entry_Index range Null_Protected_Entry .. Max_Protected_Entry; subtype Positive_Protected_Entry_Index is Protected_Entry_Index range 1 .. Protected_Entry_Index'Last; type Protection (Num_Entries : Protected_Entry_Index) is private; -- This type contains the GNARL state of a protected object. The -- application-defined portion of the state (i.e. private objects) -- is maintained by the compiler-generated code. type Protection_Access is access all Protection; Null_PO : constant Protection_Access := null; type Communication_Block is private; -- Objects of this type are passed between GNARL calls to allow RTS -- information to be preserved. ------------------------------------ -- Rendezvous related definitions -- ------------------------------------ Null_Task_Entry : constant := Null_Entry; Max_Task_Entry : constant := Max_Entry; type Task_Entry_Index is new Entry_Index range Null_Task_Entry .. Max_Task_Entry; type Task_Entry_Queue_Array is array (Task_Entry_Index range <>) of Entry_Queue; No_Rendezvous : constant := 0; Max_Select : constant Integer := Integer'Last; -- RTS-defined subtype Select_Index is Integer range No_Rendezvous .. Max_Select; -- type Select_Index is range No_Rendezvous .. Max_Select; subtype Positive_Select_Index is Select_Index range 1 .. Select_Index'Last; type Accept_Alternative is record -- should be packed Null_Body : Boolean; S : Task_Entry_Index; end record; type Accept_List is array (Positive_Select_Index range <>) of Accept_Alternative; type Accept_List_Access is access constant Accept_List; ---------------------------------- -- Entry_Call_Record definition -- ---------------------------------- type Entry_Call_Record is record Prev : Entry_Call_Link; Next : Entry_Call_Link; Self : Task_ID; Level : ATC_Level; -- One of Self and Level are redundant in this implementation, since -- each Entry_Call_Record is at Self.Entry_Calls (Level). Since we must -- have access to the entry call record to be reading this, we could -- get Self from Level, or Level from Self. However, this requires -- non-portable address arithmetic. Mode : Call_Modes; Abortable : Boolean; -- This call is queued abortably. -- Protection: Acceptor.L. If the call is not on a queue, it should -- only be accessed by the task doing the call or requeue, and the -- mutex need not be locked in those cases. Done : Boolean; -- The call has been completed. -- Protection : Self.L, except in certain circumstances where -- Self knows that the acceptor is suspended waiting for a call, -- and Self holds the acceptor's mutex. Has_Been_Abortable : Boolean; -- The call has been blocked abortably at some point. -- Currently only used for protected entry calls. -- Protection: Called_PO.L. E : Entry_Index; Prio : System.Any_Priority; -- The above fields are those that there may be some hope of packing. -- They are gathered together to allow for compilers that lay records -- out contiguously, to allow for such packing. Uninterpreted_Data : System.Address; Exception_To_Raise : System.Compiler_Exceptions.Exception_ID; -- The exception to raise once this call has been completed without -- being aborted. -- Server : Server_Record; Called_Task : Task_ID; -- For task entry calls only. Only one of Called_Task and Called_PO -- are valid; the other must be Null_Task or null, respectively. -- In general, Called_Task must be either a legitimate Task_ID or -- Null_Task. Both Called_Task and Called_PO must be null -- if the call record is not in use. -- Protection: Called_Task.L. There are situations in which -- it is necessary to access this field given only an Entry_Call_Record. -- This is difficult, since Called_Task.L must be locked to access -- Called_Task. This is done by doing the lock and then checking -- to make sure that Called_Task has not changed; see -- System.Tasking.Utilities.Lock_Server. Acceptor_Prev_Call : Entry_Call_Link; -- For task entry calls only. Acceptor_Prev_Priority : Rendezvous_Priority; -- For task entry calls only. -- The priority of the most recent prior call being serviced. -- For protected entry calls, this function should be performed by -- GNULLI ceiling locking. Called_PO : Protection_Access; -- For protected entry calls only. Only one of Called_Task and -- Called_PO are valid; the other must be Null_Task or Null_PO, -- respectively. In general, Called_PO must be either a legitimate -- Protection_Access value or null. Both Called_Task and -- Called_PO must be null if the call record is not in use. -- Protection: Called_PO.L. See notes under Called_Task, above. end record; ------------------------------------ -- Task related other definitions -- ------------------------------------ type Activation_Chain is limited private; type Activation_Chain_Access is access all Activation_Chain; type Task_Procedure_Access is access procedure (Arg : System.Address); type Access_Boolean is access all Boolean; ---------------------------------------------- -- Ada_Task_Control_Block (ATCB) definition -- ---------------------------------------------- type Entry_Call_Array is array (ATC_Level_Index) of aliased Entry_Call_Record; -- Notes on protection (synchronization) of TRTS data structures. -- Any field of the TCB can be written by the activator of a task when the -- task is created, since no other task can access the new task's -- state until creation is complete. -- The protection for each field is described in a comment starting with -- "Protection:". -- When a lock is used to protect an ATCB field, this lock is simply named. -- Some protection is described in terms of tasks related to the -- ATCB being protected. These are: -- Self: The task which is controlled by this ATCB. -- Acceptor: A task accepting a call from Self. -- Caller: A task calling an entry of Self. -- Parent: The task executing the master on which Self depends. -- Dependent: A task dependent on Self. -- Activator: The task that created Self and initiated its activation. -- Created: A task created and activated by Self. type Ada_Task_Control_Block (Entry_Num : Task_Entry_Index) is record LL_TCB : aliased System.Task_Primitives.Task_Control_Block; -- Control block used by the underlying low-level tasking service -- (GNULLI). -- Protection: This is used only by the GNULLI implementation, which -- takes care of all of its synchronization. Task_Entry_Point : Task_Procedure_Access; -- Information needed to call the procedure containing the code for -- the body of this task. -- Protection: Part of the synchronization between Self and -- Activator. Activator writes it, once, before Self starts -- executing. Self reads it, once, as part of its execution. Task_Arg : System.Address; -- The argument to to task procedure. Currently unused; this will -- provide a handle for discriminant information. -- Protection: Part of the synchronization between Self and -- Activator. Activator writes it, once, before Self starts -- executing. Thereafter, Self only reads it. Stack_Size : Size_Type; -- Requested stack size. -- Protection: Only used by Self. Current_Priority : System.Priority; -- Active priority, except that the effects of protected object -- priority ceilings are not reflected. This only reflects explicit -- priority changes and priority inherited through task activation -- and rendezvous. -- Ada 95 notes: In Ada 95, this field will be transferred to the -- Priority field of an Entry_Calls component when an entry call -- is initiated. The Priority of the Entry_Calls component will not -- change for the duration of the call. The accepting task can -- use it to boost its own priority without fear of its changing in -- the meantime. -- This can safely be used in the priority ordering -- of entry queues. Once a call is queued, its priority does not -- change. -- Since an entry call cannot be made while executing -- a protected action, the priority of a task will never reflect a -- priority ceiling change at the point of an entry call. -- Protection: Only written by Self, and only accessed when Acceptor -- accepts an entry or when Created activates, at which points Self is -- suspended. Base_Priority : System.Priority; -- Base priority, not changed during entry calls, only changed -- via dynamic priorities package. -- Protection: Only written by Self, accessed by anyone. New_Base_Priority : System.Priority; -- New value for Base_Priority (for dynamic priorities package). -- Protection: Self.L. L : System.Task_Primitives.Lock; -- General purpose lock; protects most fields in the ATCB. Compiler_Data : System.Address; -- Untyped task-specific data needed by the compiler to store -- per-task structures. -- Protection: Only accessed by Self. -- the following declarations are for Rendezvous Cond : System.Task_Primitives.Condition_Variable; -- Used by Self to wait for a condition to become true. -- It is invariant in the GNARL that a task waits only on its -- own condition variable. -- Protection: Condition variables are always associated with a lock. -- The runtime places no restrictions on which lock is used, except -- that it must protection the condition upon which the task is waiting. All_Tasks_Link : Task_ID; -- Used to link this task to the list of all tasks in the system. -- Protection: All_Tasks.L. Global_Task_Lock_Nesting : Natural; -- This is the current nesting level of calls to -- System.Tasking.Stages.Lock_Task_T. -- This allows a task to call Lock_Task_T multiple times without -- deadlocking. A task only locks All_Task_Lock when its -- All_Tasks_Nesting goes from 0 to 1, and only unlocked when it -- goes from 1 to 0. -- Protection: Only accessed by Self. Activation_Link : Task_ID; -- Used to link this task to a list of tasks to be activated. -- Protection: Only used by Activator. Open_Accepts : Accept_List_Access; -- This points to the Open_Accepts array of accept alternatives passed -- to the RTS by the compiler-generated code to Selective_Wait. -- Protection: Self.L. Exception_To_Raise : System.Compiler_Exceptions.Exception_ID; Exception_Address : System.Address; -- An exception which should be raised by this task when it regains -- control, and the address at which it should be raised. -- Protection: Read only by Self, under circumstances where it will -- be notified by the writer when it is safe to read it: -- 1. Written by Acceptor, when Self is suspended. -- 2. Written by Notify_Exception, executed by Self through a -- synchronous signal handler, which redirects control to a -- routine to read it and raise the exception. Chosen_Index : Select_Index; -- The index in Open_Accepts of the entry call accepted by a selective -- wait executed by this task. -- Protection: Written by both Self and Caller. Usually protected -- by Self.L. However, once the selection is known to have been -- written it can be accessed without protection. This happens -- after Self has updated it itself using information from a suspended -- Caller, or after Caller has updated it and awakened Self. Call : Entry_Call_Link; -- The entry call that has been accepted by this task. -- Protection: Self.L. Self will modify this field -- when Self.Accepting is False, and will not need the mutex to do so. -- Once a task sets Stage=Completing, no other task can access this -- field. -- The following fields are used to manage the task's life cycle. Activator : Task_ID; -- The task that created this task, either by declaring it as a task -- object or by executing a task allocator. -- Protection: Set by Activator before Self is activated, and -- read after Self is activated. Parent : Task_ID; Master_of_Task : Master_ID; -- The task executing the master of this task, and the ID of this task's -- master (unique only among masters currently active within Parent). -- Protection: Set by Activator before Self is activated, and -- read after Self is activated. Master_Within : Master_ID; -- The ID of the master currently executing within this task; that is, -- the most deeply nested currently active master. -- Protection: Only written by Self, and only read by Self or by -- dependents when Self is attempting to exit a master. Since Self -- will not write this field until the master is complete, the -- synchronization should be adequate to prevent races. Activation_Count : Integer; -- This is the number of tasks that this task is activating, i.e. the -- children that have started activation but have not completed it. -- Protection: Self.L and Created.L. Both mutexes must be locked, -- since Self.Activation_Count and Created.Stage must be synchronized. Awake_Count : Integer; -- Number of tasks dependent on this task (including this task) that are -- still "awake": not terminated and not waiting on a terminate -- alternative. -- Protection: Self.L. Parent.L must also be locked when this is -- updated, so that it can be synchronized with -- Parent.Awaited_Dependent_Count, except under special circumstances -- where we know that the two can be out of sync without allowing the -- parent to terminate before its dependents. Awaited_Dependent_Count : Integer; -- This is the awake count of a master being completed by this task. -- Protection: Self.L. Dependent.L must also be locked so that -- this field and Dependent.Awake_Count can be synchronized, except -- under special circumstances where we know that the two can be out -- of sync without allowing the parent to terminate before its -- dependents. Terminating_Dependent_Count : Integer; -- This is the count of tasks dependent on a master being completed by -- this task which are waiting on a terminate alternative. Only valid -- when there none of the dependents are awake. -- Protection: Self.L. Pending_Priority_Change : Boolean; -- Flag to indicate pending priority change (for dynamic priorities -- package). The base priority is updated on the next abortion -- completion point (aka. synchronization point). -- Protection: Self.L. Pending_Action : Boolean; -- Unified flag indicating pending action on abortion completion -- point (aka. synchronization point). Currently set if: -- . Pending_Priority_Change is set or -- . Pending_ATC_Level is changed. -- Protection: Self.L. Pending_ATC_Level : ATC_Level_Base; -- The ATC level to which this task is currently being aborted. -- Protection: Self.L. ATC_Nesting_Level : ATC_Level; -- The dynamic level of ATC nesting (currently executing nested -- asynchronous select statements) in this task. -- Protection: This is only used by Self. However, decrementing it -- in effect deallocates an Entry_Calls component, and care must be -- taken that all references to that component are eliminated before -- doing the decrement. This in turn will probably required locking -- a protected object (for a protected entry call) or the Acceptor's -- lock (for a task entry call). However, ATC_Nesting_Level itself can -- be accessed without a lock. Deferral_Level : Natural; -- This is the number of times that Defer_Abortion has been called by -- this task without a matching Undefer_Abortion call. Abortion is -- only allowed when this zero. -- Protection: Only updated by Self; access assumed to be atomic. Elaborated : Access_Boolean; -- Pointer to a flag indicating that this task's body has been -- elaborated. The flag is created and managed by the -- compiler-generated code. -- Protection: The field itself is only accessed by Activator. The flag -- that it points to is updated by Master and read by Activator; access -- is assumed to be atomic. Stage : Task_Stage; -- The general stage of the task in it's life cycle. -- Protection: Self.L. -- beginning of flags Cancel_Was_Successful : Boolean; -- This indicates that the last attempt to cancel an entry call was -- successful. It needs to be accurate between a call to -- *Cancel_*_Entry_Call and the following call to Complete_*_Entry_Call. -- These calls cannot be nested; that is, there can be no intervening -- *Cancel_*_Entry_Call, so this single field is adequate. -- Protection: Accessed only by Self. Accepting : Accepting_State; -- The ability of this task to accept an entry call. -- Protection: Self.L. Aborting : Boolean; -- Self is in the process of aborting. While set, prevents multiple -- abortion signals from being sent by different aborter while abortion -- is acted upon. This is essential since an aborter which calls -- Abort_To_Level could set the Pending_ATC_Level to yet a lower level -- (than the current level), may be preempted and would send the -- abortion signal when resuming execution. At this point, the abortee -- may have completed abortion to the proper level such that the -- signal (and resulting abortion exception) are not handled any more. -- In other words, the flag prevents a race between multiple aborters -- and the abortee. -- Protection: Self.L. -- end of flags Entry_Calls : Entry_Call_Array; -- An array of entry calls. -- Protection: The elements of this array are on entry call queues -- associated with protected objects or task entries, and are protected -- by the protected object lock or Acceptor.L, respectively. Entry_Queues : Task_Entry_Queue_Array (1 .. Entry_Num); -- An array of task entry queues. -- Protection: Self.L. Once a task has set Self.Stage to Completing, it -- has exclusive access to this field. Aborter_Link : Task_ID; -- Link to the list of tasks which tries to abort this task but -- blocked by another aborter who has already been aborting the task. Terminate_Alternative : Boolean; -- Task is accepting Select with Terminate Alternative. end record; type Barrier_Function_Pointer is access function (O : System.Address; E : Protected_Entry_Index) return Boolean; -- Pointer to a function which evaluates the barrier of a protected -- entry body. O is a pointer to the compiler-generated record -- representing the protected object, and E is the index of the -- entry serviced by the body. type Entry_Action_Pointer is access procedure (O : System.Address; P : System.Address; E : Protected_Entry_Index); -- Pointer to a procedure which executes the sequence of statements -- of a protected entry body. O is a pointer to the compiler-generated -- record representing the protected object, P is a pointer to the -- record of entry parameters, and E is the index of the -- entry serviced by the body. type Entry_Body is record Barrier : Barrier_Function_Pointer; Action : Entry_Action_Pointer; end record; -- The compiler-generated code passes objects of this type to the GNARL -- to allow it to access the executable code of an entry body. type Protected_Entry_Body_Array is array (Positive_Protected_Entry_Index range <>) of Entry_Body; -- This is an array of the executable code for all entry bodies of -- a protected type. type Protected_Entry_Body_Access is access all Protected_Entry_Body_Array; private Null_Task : constant Task_ID := null; type Activation_Chain is new Task_ID; type Master_ID is new Integer; type Communication_Block is record Self : Task_ID; Enqueued : Boolean := False; Cancelled : Boolean; end record; type Protected_Entry_Queue_Array is array (Protected_Entry_Index range <>) of Entry_Queue; type Protection (Num_Entries : Protected_Entry_Index) is new Ada.Finalization.Controlled with record L : Task_Primitives.Lock; Compiler_Info : System.Address; Call_In_Progress : Entry_Call_Link; Ceiling : System.Priority; Old_Base_Priority : System.Priority; Pending_Action : Boolean; Entry_Bodies : Protected_Entry_Body_Access; Entry_Queues : Protected_Entry_Queue_Array (1 .. Num_Entries); end record; procedure Finalize (Object : in out Protection); -- Clean up a Protection object; in particular, finalize the associated -- Lock object. end System.Tasking;