blob: cf560b569fb0a297b1e773afffecce1782c9c4c4 [file] [log] [blame]
-- --
-- --
-- S Y S T E M . T A S K I N G --
-- --
-- S p e c --
-- --
-- Copyright (C) 1992-2021, 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 3, or (at your option) any later ver- --
-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
-- --
-- As a special exception under Section 7 of GPL version 3, you are granted --
-- additional permissions described in the GCC Runtime Library Exception, --
-- version 3.1, as published by the Free Software Foundation. --
-- --
-- You should have received a copy of the GNU General Public License and --
-- a copy of the GCC Runtime Library Exception along with this program; --
-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
-- <>. --
-- --
-- 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;
with Ada.Unchecked_Conversion;
with System.Multiprocessors;
with System.Parameters;
with System.Soft_Links;
with System.Stack_Usage;
with System.Task_Info;
with System.Task_Primitives;
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 two ATCBs at once, the lock with lower serial
-- number must be locked first. We avoid holding three or more ATCB locks,
-- because that can easily lead to complications that cause race conditions
-- and deadlocks.
-- 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;
for Task_Id'Size use System.Task_Primitives.Task_Address_Size;
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 Ada.Unchecked_Conversion
(System.Task_Primitives.Task_Address, Task_Id);
function To_Address is
new Ada.Unchecked_Conversion
(Task_Id, System.Task_Primitives.Task_Address);
-- Enumeration types --
type Task_States is
-- TCB initialized but not task has not been created.
-- It cannot be executing.
-- Activating,
-- -- ??? Temporarily at end of list for GDB compatibility
-- -- Task has been created and is being made Runnable.
-- 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.
-- 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.
-- 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.
-- Task is waiting for created tasks to complete activation
-- Task is waiting on an accept or select with terminate
-- Acceptor_Delay_Sleep,
-- -- ??? Temporarily at end of list for GDB compatibility
-- -- Task is waiting on an selective wait statement
-- Task is waiting on an entry call
-- Task is waiting to start the abortable part of an
-- asynchronous select statement.
-- Task is waiting on a select statement with only a delay
-- alternative open.
-- 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.
-- 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.
-- The task has been held by Asynchronous_Task_Control.Hold_Task
-- The task has been blocked on a system call waiting for a
-- completion event/signal to occur.
-- Task has been created and is being made Runnable
-- Task is waiting on an selective wait statement
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;
-- A data structure which contains the string names of entries and entry
-- family members.
type String_Access is access all String;
-- Entry_Call_Record definition --
type Entry_Call_State is
-- the call is not abortable, and never can be
-- the call is not abortable, but may become so
-- the call is not abortable, but once was
-- the call is abortable
-- the call has been completed
-- the call was asynchronous, and was cancelled
pragma Ordered (Entry_Call_State);
-- 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 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.
-- Dispatching domain definitions --
-- We need to redefine here these types (already defined in
-- System.Multiprocessor.Dispatching_Domains) for avoiding circular
-- dependencies.
type Dispatching_Domain is
array (System.Multiprocessors.CPU range <>) of Boolean;
-- A dispatching domain needs to contain the set of processors belonging
-- to it. This is a processor mask where a True indicates that the
-- processor belongs to the dispatching domain.
-- Do not use the full range of CPU_Range because it would create a very
-- long array. This way we can use the exact range of processors available
-- in the system.
type Dispatching_Domain_Access is access Dispatching_Domain;
System_Domain : Dispatching_Domain_Access;
-- All processors belong to default system dispatching domain at start up.
-- We use a pointer which creates the actual variable for the reasons
-- explained bellow in Dispatching_Domain_Tasks.
Dispatching_Domains_Frozen : Boolean := False;
-- True when the main procedure has been called. Hence, no new dispatching
-- domains can be created when this flag is True.
type Array_Allocated_Tasks is
array (System.Multiprocessors.CPU range <>) of Natural;
-- At start-up time, we need to store the number of tasks attached to
-- concrete processors within the system domain (we can only create
-- dispatching domains with processors belonging to the system domain and
-- without tasks allocated).
type Array_Allocated_Tasks_Access is access Array_Allocated_Tasks;
Dispatching_Domain_Tasks : Array_Allocated_Tasks_Access;
-- We need to store whether there are tasks allocated to concrete
-- processors in the default system dispatching domain because we need to
-- check it before creating a new dispatching domain. Two comments about
-- why we use a pointer here and not in package Dispatching_Domains:
-- 1) We use an array created dynamically in procedure Initialize which
-- is called at the beginning of the initialization of the run-time
-- library. Declaring a static array here in the spec would not work
-- across different installations because it would get the value of
-- Number_Of_CPUs from the machine where the run-time library is built,
-- and not from the machine where the application is executed. That is
-- the reason why we create the array (CPU'First .. Number_Of_CPUs) at
-- execution time in the procedure body, ensuring that the function
-- Number_Of_CPUs is executed at execution time (the same trick as we
-- use for System_Domain).
-- 2) We have moved this declaration from package Dispatching_Domains
-- because when we use a pragma CPU, the affinity is passed through the
-- call to Create_Task. Hence, at this point, we may need to update the
-- number of tasks associated to the processor, but we do not want to
-- force a dependency from this package on Dispatching_Domains.
-- Task related other definitions --
type Activation_Chain is limited private;
-- Linked list of to-be-activated tasks, linked through
-- Activation_Link. The order of tasks on the list is irrelevant, because
-- the priority rules will ensure that they actually start activating in
-- priority order.
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;
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.
type Bit_Array is array (Integer range <>) of Boolean;
pragma Pack (Bit_Array);
subtype Debug_Event_Array is Bit_Array (1 .. 16);
Global_Task_Debug_Event_Set : Boolean := False;
-- Set True when running under debugger control and a task debug event
-- signal has been requested.
-- 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 limited 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
Base_CPU : System.Multiprocessors.CPU_Range;
-- Base CPU, only changed via dispatching domains package.
-- Protection: Self.L
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 .. System.Parameters.Max_Task_Image_Length);
-- 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 = Level_Completed_Task, 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_Alternate_Stack : System.Address;
-- The address of the alternate signal stack for this task, if any
-- Protection: Only accessed by Self
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;
pragma Atomic (Activator);
-- 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 modified by Self after that. Can be read by any task via
-- Ada.Task_Identification.Activation_Is_Complete; hence Atomic.
Wait_Count : Natural;
-- 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 activated, but have not yet terminated, and are 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 information 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
Debug_Events : Debug_Event_Array;
-- Word length array of per task debug events, of which 11 kinds are
-- currently defined in System.Tasking.Debugging package.
Domain : Dispatching_Domain_Access;
-- Domain is the dispatching domain to which the task belongs. It is
-- only changed via dispatching domains package. This field is made
-- part of the Common_ATCB, even when restricted run-times (namely
-- Ravenscar) do not use it, because this way the field is always
-- available to the underlying layers to set the affinity and we do not
-- need to do different things depending on the situation.
-- 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
limited 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 by 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 1 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. Foreign threads which are detected by
-- the run-time have a level of 0, allowing these tasks to be easily
-- distinguished if needed.
Foreign_Task_Level : constant Master_Level := 0;
Environment_Task_Level : constant Master_Level := 1;
Independent_Task_Level : constant Master_Level := 2;
Library_Task_Level : constant Master_Level := 3;
-- Note that the value of Library_Task_Level is also hard coded in the
-- compiler, see Rtsfind.Library_Task_Level. The two should be kept in
-- sync.
-- 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;
-- Affinity info --
Unspecified_CPU : constant := -1;
-- No affinity specified
-- 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;
-- The maximum number of nested asynchronous select statements supported
-- by the runtime.
subtype ATC_Level_Base is Integer range -1 .. Max_ATC_Nesting;
-- Indicates the number of nested asynchronous task control statements
-- or entries a task is in.
Level_Completed_Task : constant ATC_Level_Base := -1;
-- ATC_Level of a task that has "completed". A task reaches the completed
-- state after an abort, exception propagation, or normal exit.
Level_No_ATC_Occurring : constant ATC_Level_Base := 0;
-- ATC_Level of a task not executing a entry call or an asynchronous
-- select statement.
Level_No_Pending_Abort : constant ATC_Level_Base := ATC_Level_Base'Last;
-- ATC_Level when there is no pending abort
subtype ATC_Level is ATC_Level_Base range
Level_No_ATC_Occurring .. Level_No_Pending_Abort - 1;
-- Nested ATC_Levels valid during the execution of a task
subtype ATC_Level_Index is ATC_Level range
Level_No_ATC_Occurring + 1 .. ATC_Level'Last;
-- ATC_Levels valid when a task is executing an entry call or asynchronous
-- task control statements.
-- 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???
With_Abort : Boolean := False;
-- Tell caller whether the call may be aborted
-- ??? consider merging this with Was_Abortable state
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;
-- Anonymous pointer used to implement task attributes (see s-tataat.adb
-- and a-tasatt.adb)
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 Atomic_Address is mod Memory_Size;
pragma Atomic (Atomic_Address);
type Attribute_Array is
array (1 .. Parameters.Max_Attribute_Count) of Atomic_Address;
-- Array of task attributes. The value (Atomic_Address) will either be
-- converted to a task attribute if it fits, or to a pointer to a record
-- by Ada.Task_Attributes.
type Task_Serial_Number is mod 2 ** Long_Long_Integer'Size;
-- Used to give each task a unique serial number. We want 64-bits for this
-- type to get as much uniqueness as possible (2**64 is operationally
-- infinite in this context, but 2**32 perhaps could recycle). We use
-- Long_Long_Integer (which in the normal case is always 64-bits) rather
-- than 64-bits explicitly to allow codepeer to analyze this unit when
-- a target configuration file forces the maximum integer size to 32.
type Ada_Task_Control_Block (Entry_Num : Task_Entry_Index) is limited 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 : Natural := 0;
-- Number of tasks directly dependent on this task (including itself)
-- that are still "alive", i.e. not terminated.
-- Protection: Self.L
Awake_Count : Natural := 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 := Level_No_ATC_Occurring;
-- 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_Abort has been called by
-- this task without a matching Undefer_Abort 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 := Level_No_Pending_Abort;
-- Indicates the ATC level to which this task is currently being
-- aborted. Two special values exist:
-- * Level_Completed_Task: the task has completed.
-- * Level_No_Pending_Abort: the task is not being aborted to any
-- level.
-- All other values indicate 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;
-- Monotonic counter 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.
Free_On_Termination : Boolean := False;
-- Deallocate the ATCB when the task terminates. This flag is normally
-- False, and is set True when Unchecked_Deallocation is called on a
-- non-terminated task so that the associated storage is automatically
-- reclaimed when the task terminates.
Attributes : Attribute_Array := (others => 0);
-- Task attributes
-- IMPORTANT Note: the Entry_Queues field is last for efficiency of
-- access to other fields, do not put new fields after this one.
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;
Base_CPU : System.Multiprocessors.CPU_Range;
Domain : Dispatching_Domain_Access;
Task_Info : System.Task_Info.Task_Info_Type;
Stack_Size : System.Parameters.Size_Type;
T : Task_Id;
Success : out Boolean);
-- Initialize fields of the TCB for task T, and link into global TCB
-- structures. Call this only with abort deferred and holding RTS_Lock.
-- Self_ID is the calling task (normally the activator of T). Success is
-- set to indicate whether the TCB was successfully initialized.
Null_Task : constant Task_Id := null;
type Activation_Chain is limited record
T_ID : Task_Id;
end record;
-- 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). The "limited" forces
-- Activation_Chain to be a by-reference type; see RM-6.2(4).
function Number_Of_Entries (Self_Id : Task_Id) return Entry_Index;
-- Given a task, return the number of entries it contains
end System.Tasking;