| ------------------------------------------------------------------------------ |
| -- -- |
| -- GNU ADA RUN-TIME LIBRARY (GNARL) COMPONENTS -- |
| -- -- |
| -- S Y S T E M . T A S K I N G -- |
| -- -- |
| -- S p e c -- |
| -- -- |
| -- $Revision: 1.89 $ |
| -- -- |
| -- Copyright (C) 1992-2001, 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, 59 Temple Place - Suite 330, Boston, -- |
| -- MA 02111-1307, 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. It is -- |
| -- now maintained by Ada Core Technologies Inc. in cooperation with Florida -- |
| -- State University (http://www.gnat.com). -- |
| -- -- |
| ------------------------------------------------------------------------------ |
| |
| -- 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 |
| |
| with System.Parameters; |
| -- used for Size_Type |
| |
| with System.Task_Info; |
| -- used for Task_Info_Type, Task_Image_Type |
| |
| with System.Soft_Links; |
| -- used for TSD |
| |
| with System.Task_Primitives; |
| -- used for Private_Data |
| -- Lock (in System.Tasking.Protected_Objects) |
| |
| with Unchecked_Conversion; |
| |
| package System.Tasking is |
| |
| -- ------------------- |
| -- -- 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 |
| -- number is the number at the left.) |
| -- |
| -- 1. System.Tasking.PO_Simple.Protection.L (any PO lock) |
| -- 2. System.Tasking.Initialization.Global_Task_Lock (in body) |
| -- 3. System.Tasking.Task_Attributes.All_Attrs_L |
| -- 4. System.Task_Primitives.Operations.All_Tasks_L |
| -- 5. System.Interrupts.L (in body) |
| -- 6. 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. |
| -- |
| -- Sometime 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. |
| -- |
| -- For interrupt-handler state, we have a special locking rule. |
| -- See System.Interrupts (spec) for explanation. |
| |
| --------------------------------- |
| -- 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 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 -- |
| ---------------------------------------------- |
| |
| -- 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, Call and LL fields. |
| |
| ---------------------------------------------------------------------- |
| -- Common ATCB section -- |
| -- -- |
| -- This section is 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. |
| |
| Task_Image : System.Task_Info.Task_Image_Type; |
| -- holds an access to string that provides a readable id for task, |
| -- built from the variable of which it is a value or component. |
| |
| 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. 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. |
| |
| 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: All_Tasks.L. |
| |
| 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. |
| 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 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. |
| |
| 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. |
| -- If it has succeeded, State = Cancelled. |
| -- ????? |
| -- 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; |
| |
| ---------------------------------------------- |
| -- Ada_Task_Control_Block (ATCB) definition -- |
| ---------------------------------------------- |
| |
| type Entry_Call_Array is array (ATC_Level_Index) of |
| aliased Entry_Call_Record; |
| |
| D_I_Count : constant := 2; |
| -- This constant may be adjusted, to allow more Address-sized |
| -- attributes to be stored directly in the task control block. |
| |
| subtype Direct_Index is Integer range 0 .. D_I_Count - 1; |
| -- 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_Array is |
| array (Direct_Index) of aliased System.Address; |
| |
| type Direct_Index_Vector is mod 2 ** D_I_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. |
| |
| Global_Task_Lock_Nesting : Natural := 0; |
| -- 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. |
| |
| 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 |
| -- 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. |
| |
| 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 abortion |
| -- 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 : Integer := 0; |
| -- user-writeable location, for use in debugging tasks; |
| -- debugger can display this value to show where the task currently |
| -- is, in user terms |
| |
| 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; |
| pragma Volatile (Ada_Task_Control_Block); |
| |
| --------------------- |
| -- Initialize_ATCB -- |
| --------------------- |
| |
| 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 : in out Task_ID; |
| Success : out Boolean); |
| -- Initialize fields of a TCB and link into global TCB structures |
| -- Call this only with abort deferred and holding All_Tasks_L. |
| |
| 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; |
