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gcc/gcc/ada/s-taskin.ads
Javier Miranda 15b540bec8 2006-10-31 Javier Miranda <miranda@adacore.com> 
* s-tpoben.ads, s-tpoben.adb, s-taprob.ads, s-taprob.adb
	(Get_Ceiling): New subprogram that returns
	the ceiling priority of the protected object.
	(Set_Ceiling): New subprogram that sets the new ceiling priority of
	the protected object.

	* s-tarest.adb: (Create_Restricted_Task): Fix potential CE.

	* s-taskin.ads, s-taskin.adb: (Storage_Size): New function.

From-SVN: r118317
2006-10-31 19:11:44 +01:00

1076 lines
42 KiB
Ada
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------------------------------------------------------------------------------
-- --
-- GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS --
-- --
-- S Y S T E M . T A S K I N G --
-- --
-- S p e c --
-- --
-- Copyright (C) 1992-2006, Free Software Foundation, Inc. --
-- --
-- GNARL is free software; you can redistribute it and/or modify it under --
-- terms of the GNU General Public License as published by the Free Soft- --
-- ware Foundation; either version 2, or (at your option) any later ver- --
-- sion. GNARL is distributed in the hope that it will be useful, but WITH- --
-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
-- or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License --
-- for more details. You should have received a copy of the GNU General --
-- Public License distributed with GNARL; see file COPYING. If not, write --
-- to the Free Software Foundation, 51 Franklin Street, Fifth Floor, --
-- Boston, MA 02110-1301, USA. --
-- --
-- As a special exception, if other files instantiate generics from this --
-- unit, or you link this unit with other files to produce an executable, --
-- this unit does not by itself cause the resulting executable to be --
-- covered by the GNU General Public License. This exception does not --
-- however invalidate any other reasons why the executable file might be --
-- covered by the GNU Public License. --
-- --
-- GNARL was developed by the GNARL team at Florida State University. --
-- Extensive contributions were provided by Ada Core Technologies, Inc. --
-- --
------------------------------------------------------------------------------
-- This package provides necessary type definitions for compiler interface
-- Note: the compiler generates direct calls to this interface, via Rtsfind.
-- Any changes to this interface may require corresponding compiler changes.
with Ada.Exceptions;
-- Used for Exception_Id
-- Exception_Occurrence
with System.Parameters;
-- used for Size_Type
with System.Task_Info;
-- used for Task_Info_Type
with System.Soft_Links;
-- used for TSD
with System.Task_Primitives;
-- used for Private_Data
with System.Stack_Usage;
-- used for Stack_Analyzer
with Unchecked_Conversion;
package System.Tasking is
pragma Preelaborate;
-------------------
-- Locking Rules --
-------------------
-- The following rules must be followed at all times, to prevent
-- deadlock and generally ensure correct operation of locking.
-- Never lock a lock unless abort is deferred
-- Never undefer abort while holding a lock
-- Overlapping critical sections must be properly nested, and locks must
-- be released in LIFO order. e.g., the following is not allowed:
-- Lock (X);
-- ...
-- Lock (Y);
-- ...
-- Unlock (X);
-- ...
-- Unlock (Y);
-- Locks with lower (smaller) level number cannot be locked
-- while holding a lock with a higher level number. (The level
-- 1. System.Tasking.PO_Simple.Protection.L (any PO lock)
-- 2. System.Tasking.Initialization.Global_Task_Lock (in body)
-- 3. System.Task_Primitives.Operations.Single_RTS_Lock
-- 4. System.Tasking.Ada_Task_Control_Block.LL.L (any TCB lock)
-- Clearly, there can be no circular chain of hold-and-wait
-- relationships involving locks in different ordering levels.
-- We used to have Global_Task_Lock before Protection.L but this was
-- clearly wrong since there can be calls to "new" inside protected
-- operations. The new ordering prevents these failures.
-- Sometimes we need to hold two ATCB locks at the same time. To allow us
-- to order the locking, each ATCB is given a unique serial number. If one
-- needs to hold locks on several ATCBs at once, the locks with lower
-- serial numbers must be locked first.
-- We don't always need to check the serial numbers, since the serial
-- numbers are assigned sequentially, and so:
-- . The parent of a task always has a lower serial number.
-- . The activator of a task always has a lower serial number.
-- . The environment task has a lower serial number than any other task.
-- . If the activator of a task is different from the task's parent,
-- the parent always has a lower serial number than the activator.
---------------------------------
-- Task_Id related definitions --
---------------------------------
type Ada_Task_Control_Block;
type Task_Id is access all Ada_Task_Control_Block;
Null_Task : constant Task_Id;
type Task_List is array (Positive range <>) of Task_Id;
function Self return Task_Id;
pragma Inline (Self);
-- This is the compiler interface version of this function. Do not call
-- from the run-time system.
function To_Task_Id is new Unchecked_Conversion (System.Address, Task_Id);
function To_Address is new Unchecked_Conversion (Task_Id, System.Address);
-----------------------
-- Enumeration types --
-----------------------
type Task_States is
(Unactivated,
-- Task has been created but has not been activated.
-- It cannot be executing.
-- Active states
-- For all states from here down, the task has been activated.
-- For all states from here down, except for Terminated, the task
-- may be executing.
-- Activator = null iff it has not yet completed activating.
-- For all states from here down,
-- the task has been activated, and may be executing.
Runnable,
-- Task is not blocked for any reason known to Ada.
-- (It may be waiting for a mutex, though.)
-- It is conceptually "executing" in normal mode.
Terminated,
-- The task is terminated, in the sense of ARM 9.3 (5).
-- Any dependents that were waiting on terminate
-- alternatives have been awakened and have terminated themselves.
Activator_Sleep,
-- Task is waiting for created tasks to complete activation
Acceptor_Sleep,
-- Task is waiting on an accept or selective wait statement
Entry_Caller_Sleep,
-- Task is waiting on an entry call
Async_Select_Sleep,
-- Task is waiting to start the abortable part of an
-- asynchronous select statement.
Delay_Sleep,
-- Task is waiting on a select statement with only a delay
-- alternative open.
Master_Completion_Sleep,
-- Master completion has two phases.
-- In Phase 1 the task is sleeping in Complete_Master
-- having completed a master within itself,
-- and is waiting for the tasks dependent on that master to become
-- terminated or waiting on a terminate Phase.
Master_Phase_2_Sleep,
-- In Phase 2 the task is sleeping in Complete_Master
-- waiting for tasks on terminate alternatives to finish
-- terminating.
-- The following are special uses of sleep, for server tasks
-- within the run-time system.
Interrupt_Server_Idle_Sleep,
Interrupt_Server_Blocked_Interrupt_Sleep,
Timer_Server_Sleep,
AST_Server_Sleep,
Asynchronous_Hold,
-- The task has been held by Asynchronous_Task_Control.Hold_Task
Interrupt_Server_Blocked_On_Event_Flag
-- The task has been blocked on a system call waiting for the
-- completion event.
);
type Call_Modes is
(Simple_Call, Conditional_Call, Asynchronous_Call, Timed_Call);
type Select_Modes is (Simple_Mode, Else_Mode, Terminate_Mode, Delay_Mode);
subtype Delay_Modes is Integer;
-------------------------------
-- 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;
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 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;
type Task_Entry_Queue_Array is
array (Task_Entry_Index range <>) of Entry_Queue;
----------------------------------
-- Entry_Call_Record definition --
----------------------------------
type Entry_Call_State is
(Never_Abortable,
-- the call is not abortable, and never can be
Not_Yet_Abortable,
-- the call is not abortable, but may become so
Was_Abortable,
-- the call is not abortable, but once was
Now_Abortable,
-- the call is abortable
Done,
-- the call has been completed
Cancelled
-- the call was asynchronous, and was cancelled
);
-- Never_Abortable is used for calls that are made in a abort
-- deferred region (see ARM 9.8(5-11), 9.8 (20)).
-- Such a call is never abortable.
-- The Was_ vs. Not_Yet_ distinction is needed to decide whether it
-- is OK to advance into the abortable part of an async. select stmt.
-- That is allowed iff the mode is Now_ or Was_.
-- Done indicates the call has been completed, without cancellation,
-- or no call has been made yet at this ATC nesting level,
-- and so aborting the call is no longer an issue.
-- Completion of the call does not necessarily indicate "success";
-- the call may be returning an exception if Exception_To_Raise is
-- non-null.
-- Cancelled indicates the call was cancelled,
-- and so aborting the call is no longer an issue.
-- The call is on an entry queue unless
-- State >= Done, in which case it may or may not be still Onqueue.
-- Please do not modify the order of the values, without checking
-- all uses of this type. We rely on partial "monotonicity" of
-- Entry_Call_Record.State to avoid locking when we access this
-- value for certain tests. In particular:
-- 1) Once State >= Done, we can rely that the call has been
-- completed. If State >= Done, it will not
-- change until the task does another entry call at this level.
-- 2) Once State >= Was_Abortable, we can rely that the call has
-- been queued abortably at least once, and so the check for
-- whether it is OK to advance to the abortable part of an
-- async. select statement does not need to lock anything.
type Restricted_Entry_Call_Record is record
Self : Task_Id;
-- ID of the caller
Mode : Call_Modes;
State : Entry_Call_State;
pragma Atomic (State);
-- Indicates part of the state of the call.
--
-- Protection: If the call is not on a queue, it should only be
-- accessed by Self, and Self does not need any lock to modify this
-- field.
--
-- Once the call is on a queue, the value should be something other
-- than Done unless it is cancelled, and access is controller by the
-- "server" of the queue -- i.e., the lock of Checked_To_Protection
-- (Call_Target) if the call record is on the queue of a PO, or the
-- lock of Called_Target if the call is on the queue of a task. See
-- comments on type declaration for more details.
Uninterpreted_Data : System.Address;
-- Data passed by the compiler
Exception_To_Raise : Ada.Exceptions.Exception_Id;
-- The exception to raise once this call has been completed without
-- being aborted.
end record;
pragma Suppress_Initialization (Restricted_Entry_Call_Record);
-------------------------------------------
-- Task termination procedure definition --
-------------------------------------------
-- We need to redefine here these types (already defined in
-- Ada.Task_Termination) for avoiding circular dependencies.
type Cause_Of_Termination is (Normal, Abnormal, Unhandled_Exception);
-- Possible causes for task termination:
--
-- Normal means that the task terminates due to completing the
-- last sentence of its body, or as a result of waiting on a
-- terminate alternative.
-- Abnormal means that the task terminates because it is being aborted
-- handled_Exception means that the task terminates because of exception
-- raised by by the execution of its task_body.
type Termination_Handler is access protected procedure
(Cause : Cause_Of_Termination;
T : Task_Id;
X : Ada.Exceptions.Exception_Occurrence);
-- Used to represent protected procedures to be executed when task
-- terminates.
------------------------------------
-- Task related other definitions --
------------------------------------
type Activation_Chain is limited private;
-- Comment required ???
type Activation_Chain_Access is access all Activation_Chain;
-- Comment required ???
type Task_Procedure_Access is access procedure (Arg : System.Address);
type Access_Boolean is access all Boolean;
function Detect_Blocking return Boolean;
pragma Inline (Detect_Blocking);
-- Return whether the Detect_Blocking pragma is enabled
function Storage_Size (T : Task_Id) return System.Parameters.Size_Type;
-- Retrieve from the TCB of the task the allocated size of its stack,
-- either the system default or the size specified by a pragma. This
-- is in general a non-static value that can depend on discriminants
-- of the task.
----------------------------------------------
-- Ada_Task_Control_Block (ATCB) definition --
----------------------------------------------
-- 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
-- Note: The order of the fields is important to implement efficiently
-- tasking support under gdb.
-- Currently gdb relies on the order of the State, Parent, Base_Priority,
-- Task_Image, Task_Image_Len, Call and LL fields.
-------------------------
-- Common ATCB section --
-------------------------
-- Section used by all GNARL implementations (regular and restricted)
type Common_ATCB is record
State : Task_States;
pragma Atomic (State);
-- Encodes some basic information about the state of a task,
-- including whether it has been activated, whether it is sleeping,
-- and whether it is terminated.
--
-- Protection: Self.L
Parent : Task_Id;
-- The task on which this task depends.
-- See also Master_Level and Master_Within.
Base_Priority : System.Any_Priority;
-- Base priority, not changed during entry calls, only changed
-- via dynamic priorities package.
--
-- Protection: Only written by Self, accessed by anyone
Current_Priority : System.Any_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.
Protected_Action_Nesting : Natural;
pragma Atomic (Protected_Action_Nesting);
-- The dynamic level of protected action nesting for this task. This
-- field is needed for checking whether potentially blocking operations
-- are invoked from protected actions. pragma Atomic is used because it
-- can be read/written from protected interrupt handlers.
Task_Image : String (1 .. 32);
-- Hold a string that provides a readable id for task,
-- built from the variable of which it is a value or component.
Task_Image_Len : Natural;
-- Actual length of Task_Image
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
-- Pending_ATC_Level = 0, no other task can access this field.
LL : aliased Task_Primitives.Private_Data;
-- 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_Arg : System.Address;
-- The argument to task procedure. 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.
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.
Compiler_Data : System.Soft_Links.TSD;
-- Task-specific data needed by the compiler to store per-task
-- structures.
--
-- Protection: Only accessed by Self
All_Tasks_Link : Task_Id;
-- Used to link this task to the list of all tasks in the system
--
-- Protection: RTS_Lock
Activation_Link : Task_Id;
-- Used to link this task to a list of tasks to be activated
--
-- Protection: Only used by Activator
Activator : Task_Id;
-- The task that created this task, either by declaring it as a task
-- object or by executing a task allocator. The value is null iff Self
-- has completed activation.
--
-- Protection: Set by Activator before Self is activated, and only read
-- and modified by Self after that.
Wait_Count : Integer;
-- This count is used by a task that is waiting for other tasks. At all
-- other times, the value should be zero. It is used differently in
-- several different states. Since a task cannot be in more than one of
-- these states at the same time, a single counter suffices.
--
-- Protection: Self.L
-- Activator_Sleep
-- 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.State must be synchronized.
-- Master_Completion_Sleep (phase 1)
-- This is the number dependent tasks of a master being completed by
-- Self that are not activated, not terminated, and not waiting on a
-- terminate alternative.
-- Master_Completion_2_Sleep (phase 2)
-- This is the count of tasks dependent on a master being completed by
-- Self which are waiting on a terminate alternative.
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.
Activation_Failed : Boolean;
-- Set to True if activation of a chain of tasks fails,
-- so that the activator should raise Tasking_Error.
Task_Info : System.Task_Info.Task_Info_Type;
-- System-specific attributes of the task as specified by the
-- Task_Info pragma.
Analyzer : System.Stack_Usage.Stack_Analyzer;
-- For storing informations used to measure the stack usage
Global_Task_Lock_Nesting : Natural;
-- This is the current nesting level of calls to
-- System.Tasking.Initialization.Lock_Task. This allows a task to call
-- Lock_Task multiple times without deadlocking. A task only locks
-- Global_Task_Lock when its Global_Task_Lock_Nesting goes from 0 to 1,
-- and only unlocked when it goes from 1 to 0.
--
-- Protection: Only accessed by Self
Fall_Back_Handler : Termination_Handler;
-- This is the fall-back handler that applies to the dependent tasks of
-- the task.
--
-- Protection: Self.L
Specific_Handler : Termination_Handler;
-- This is the specific handler that applies only to this task, and not
-- any of its dependent tasks.
--
-- Protection: Self.L
end record;
---------------------------------------
-- Restricted_Ada_Task_Control_Block --
---------------------------------------
-- This type should only be used by the restricted GNARLI and by
-- restricted GNULL implementations to allocate an ATCB (see
-- System.Task_Primitives.Operations.New_ATCB) that will take
-- significantly less memory.
-- Note that the restricted GNARLI should only access fields that are
-- present in the Restricted_Ada_Task_Control_Block structure.
type Restricted_Ada_Task_Control_Block (Entry_Num : Task_Entry_Index) is
record
Common : Common_ATCB;
-- The common part between various tasking implementations
Entry_Call : aliased Restricted_Entry_Call_Record;
-- Protection: This field is used on entry call "queues" associated
-- with protected objects, and is protected by the protected object
-- lock.
end record;
pragma Suppress_Initialization (Restricted_Ada_Task_Control_Block);
Interrupt_Manager_ID : Task_Id;
-- This task ID is declared here to break circular dependencies.
-- Also declare Interrupt_Manager_ID after Task_Id is known, to avoid
-- generating unneeded finalization code.
-----------------------
-- List of all Tasks --
-----------------------
All_Tasks_List : Task_Id;
-- Global linked list of all tasks
------------------------------------------
-- Regular (non restricted) definitions --
------------------------------------------
--------------------------------
-- Master Related Definitions --
--------------------------------
subtype Master_Level is Integer;
subtype Master_ID is Master_Level;
-- Normally, a task starts out with internal master nesting level one
-- larger than external master nesting level. It is incremented to one by
-- Enter_Master, which is called in the task body only if the compiler
-- thinks the task may have dependent tasks. It is set to for the
-- environment task, the level 2 is reserved for server tasks of the
-- run-time system (the so called "independent tasks"), and the level 3 is
-- for the library level tasks.
Environment_Task_Level : constant Master_Level := 1;
Independent_Task_Level : constant Master_Level := 2;
Library_Task_Level : constant Master_Level := 3;
------------------------------
-- Task size, priority info --
------------------------------
Unspecified_Priority : constant Integer := System.Priority'First - 1;
Priority_Not_Boosted : constant Integer := System.Priority'First - 1;
-- Definition of Priority actually has to come from the RTS configuration
subtype Rendezvous_Priority is Integer
range Priority_Not_Boosted .. System.Any_Priority'Last;
------------------------------------
-- Rendezvous related definitions --
------------------------------------
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
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;
-----------------------------------
-- 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 0 .. ATC_Level_Base'Last - 1;
subtype ATC_Level_Index is ATC_Level range 1 .. ATC_Level'Last;
----------------------------------
-- Entry_Call_Record definition --
----------------------------------
type Entry_Call_Record is record
Self : Task_Id;
-- ID of the caller
Mode : Call_Modes;
State : Entry_Call_State;
pragma Atomic (State);
-- Indicates part of the state of the call
--
-- Protection: If the call is not on a queue, it should only be
-- accessed by Self, and Self does not need any lock to modify this
-- field. Once the call is on a queue, the value should be something
-- other than Done unless it is cancelled, and access is controller by
-- the "server" of the queue -- i.e., the lock of Checked_To_Protection
-- (Call_Target) if the call record is on the queue of a PO, or the
-- lock of Called_Target if the call is on the queue of a task. See
-- comments on type declaration for more details.
Uninterpreted_Data : System.Address;
-- Data passed by the compiler
Exception_To_Raise : Ada.Exceptions.Exception_Id;
-- The exception to raise once this call has been completed without
-- being aborted.
Prev : Entry_Call_Link;
Next : Entry_Call_Link;
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.
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.
Called_Task : Task_Id;
pragma Atomic (Called_Task);
-- Use for task entry calls. The value is null if the call record is
-- not in use. Conversely, unless State is Done and Onqueue is false,
-- Called_Task points to an ATCB.
--
-- Protection: Called_Task.L
Called_PO : System.Address;
pragma Atomic (Called_PO);
-- Similar to Called_Task but for protected objects
--
-- Note that the previous implementation tried to merge both
-- Called_Task and Called_PO but this ended up in many unexpected
-- complications (e.g having to add a magic number in the ATCB, which
-- caused gdb lots of confusion) with no real gain since the
-- Lock_Server implementation still need to loop around chasing for
-- pointer changes even with a single pointer.
Acceptor_Prev_Call : Entry_Call_Link;
-- For task entry calls only
Acceptor_Prev_Priority : Rendezvous_Priority := Priority_Not_Boosted;
-- 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.
Cancellation_Attempted : Boolean := False;
pragma Atomic (Cancellation_Attempted);
-- Cancellation of the call has been attempted.
-- Consider merging this into State???
Requeue_With_Abort : Boolean := False;
-- Temporary to tell caller whether requeue is with abort.
-- Find a better way of doing this ???
Needs_Requeue : Boolean := False;
-- Temporary to tell acceptor of task entry call that
-- Exceptional_Complete_Rendezvous needs to do requeue.
end record;
------------------------------------
-- Task related other definitions --
------------------------------------
type Access_Address is access all System.Address;
-- Comment on what this is used for ???
pragma No_Strict_Aliasing (Access_Address);
-- This type is used in contexts where aliasing may be an issue (see
-- for example s-tataat.adb), so we avoid any incorrect aliasing
-- assumptions.
----------------------------------------------
-- Ada_Task_Control_Block (ATCB) definition --
----------------------------------------------
type Entry_Call_Array is array (ATC_Level_Index) of
aliased Entry_Call_Record;
type Direct_Index is range 0 .. Parameters.Default_Attribute_Count;
subtype Direct_Index_Range is Direct_Index range 1 .. Direct_Index'Last;
-- Attributes with indices in this range are stored directly in the task
-- control block. Such attributes must be Address-sized. Other attributes
-- will be held in dynamically allocated records chained off of the task
-- control block.
type Direct_Attribute_Element is mod Memory_Size;
pragma Atomic (Direct_Attribute_Element);
type Direct_Attribute_Array is
array (Direct_Index_Range) of aliased Direct_Attribute_Element;
type Direct_Index_Vector is mod 2 ** Parameters.Default_Attribute_Count;
-- This is a bit-vector type, used to store information about
-- the usage of the direct attribute fields.
type Task_Serial_Number is mod 2 ** 64;
-- Used to give each task a unique serial number
type Ada_Task_Control_Block (Entry_Num : Task_Entry_Index) is record
Common : Common_ATCB;
-- The common part between various tasking implementations
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.
New_Base_Priority : System.Any_Priority;
-- New value for Base_Priority (for dynamic priorities package)
--
-- Protection: Self.L
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. It is
-- non-null iff this task is ready to accept an entry call.
--
-- Protection: Self.L
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.
Master_of_Task : Master_Level;
-- 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_Level;
-- 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.
Alive_Count : Integer := 0;
-- Number of tasks directly dependent on this task (including itself)
-- that are still "alive", i.e. not terminated.
--
-- Protection: Self.L
Awake_Count : Integer := 0;
-- Number of tasks directly dependent on this task (including itself)
-- still "awake", i.e., are not terminated and not waiting on a
-- terminate alternative.
--
-- Invariant: Awake_Count <= Alive_Count
-- Protection: Self.L
-- Beginning of flags
Aborting : Boolean := False;
pragma Atomic (Aborting);
-- Self is in the process of aborting. While set, prevents multiple
-- abort signals from being sent by different aborter while abort
-- 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
-- abort signal when resuming execution. At this point, the abortee
-- may have completed abort to the proper level such that the
-- signal (and resulting abort exception) are not handled any more.
-- In other words, the flag prevents a race between multiple aborters
--
-- Protection: protected by atomic access.
ATC_Hack : Boolean := False;
pragma Atomic (ATC_Hack);
-- ?????
-- Temporary fix, to allow Undefer_Abort to reset Aborting in the
-- handler for Abort_Signal that encloses an async. entry call.
-- For the longer term, this should be done via code in the
-- handler itself.
Callable : Boolean := True;
-- It is OK to call entries of this task
Dependents_Aborted : Boolean := False;
-- This is set to True by whichever task takes responsibility for
-- aborting the dependents of this task.
--
-- Protection: Self.L
Interrupt_Entry : Boolean := False;
-- Indicates if one or more Interrupt Entries are attached to the task.
-- This flag is needed for cleaning up the Interrupt Entry bindings.
Pending_Action : Boolean := False;
-- Unified flag indicating some action needs to be take when abort
-- next becomes undeferred. Currently set if:
-- . Pending_Priority_Change is set
-- . Pending_ATC_Level is changed
-- . Requeue involving POs
-- (Abortable field may have changed and the Wait_Until_Abortable
-- has to recheck the abortable status of the call.)
-- . Exception_To_Raise is non-null
--
-- Protection: Self.L
--
-- This should never be reset back to False outside of the procedure
-- Do_Pending_Action, which is called by Undefer_Abort. It should only
-- be set to True by Set_Priority and Abort_To_Level.
Pending_Priority_Change : Boolean := False;
-- Flag to indicate pending priority change (for dynamic priorities
-- package). The base priority is updated on the next abort
-- completion point (aka. synchronization point).
--
-- Protection: Self.L
Terminate_Alternative : Boolean := False;
-- Task is accepting Select with Terminate Alternative
--
-- Protection: Self.L
-- End of flags
-- Beginning of counts
ATC_Nesting_Level : ATC_Level := 1;
-- The dynamic level of ATC nesting (currently executing nested
-- asynchronous select statements) in this task.
-- Protection: Self_ID.L. Only Self reads or updates this field.
-- Decrementing it 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 require locking a protected
-- object (for a protected entry call) or the Acceptor's lock (for a
-- task entry call). No other task should attempt to read or modify
-- this value.
Deferral_Level : Natural := 1;
-- 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. It is initially 1, to protect the task at
-- startup.
-- Protection: Only updated by Self; access assumed to be atomic
Pending_ATC_Level : ATC_Level_Base := ATC_Level_Infinity;
-- The ATC level to which this task is currently being aborted. If the
-- value is zero, the entire task has "completed". That may be via
-- abort, exception propagation, or normal exit. If the value is
-- ATC_Level_Infinity, the task is not being aborted to any level. If
-- the value is positive, the task has not completed. This should ONLY
-- be modified by Abort_To_Level and Exit_One_ATC_Level.
--
-- Protection: Self.L
Serial_Number : Task_Serial_Number;
-- A growing number to provide some way to check locking rules/ordering
Known_Tasks_Index : Integer := -1;
-- Index in the System.Tasking.Debug.Known_Tasks array
User_State : Long_Integer := 0;
-- User-writeable location, for use in debugging tasks; also provides a
-- simple task specific data.
Direct_Attributes : Direct_Attribute_Array;
-- For task attributes that have same size as Address
Is_Defined : Direct_Index_Vector := 0;
-- Bit I is 1 iff Direct_Attributes (I) is defined
Indirect_Attributes : Access_Address;
-- A pointer to chain of records for other attributes that are not
-- address-sized, including all tagged types.
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.
end record;
--------------------
-- Initialization --
--------------------
procedure Initialize;
-- This procedure constitutes the first part of the initialization of the
-- GNARL. This includes creating data structures to make the initial thread
-- into the environment task. The last part of the initialization is done
-- in System.Tasking.Initialization or System.Tasking.Restricted.Stages.
-- All the initializations used to be in Tasking.Initialization, but this
-- is no longer possible with the run time simplification (including
-- optimized PO and the restricted run time) since one cannot rely on
-- System.Tasking.Initialization being present, as was done before.
procedure Initialize_ATCB
(Self_ID : Task_Id;
Task_Entry_Point : Task_Procedure_Access;
Task_Arg : System.Address;
Parent : Task_Id;
Elaborated : Access_Boolean;
Base_Priority : System.Any_Priority;
Task_Info : System.Task_Info.Task_Info_Type;
Stack_Size : System.Parameters.Size_Type;
T : Task_Id;
Success : out Boolean);
-- Initialize fields of a TCB and link into global TCB structures Call
-- this only with abort deferred and holding RTS_Lock. Need more
-- documentation, mention T, and describe Success ???
private
Null_Task : constant Task_Id := null;
type Activation_Chain is record
T_ID : Task_Id;
end record;
pragma Volatile (Activation_Chain);
-- Activation_chain is an in-out parameter of initialization procedures
-- and it must be passed by reference because the init proc may terminate
-- abnormally after creating task components, and these must be properly
-- registered for removal (Expunge_Unactivated_Tasks).
end System.Tasking;
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