------------------------------------------------------------------------------ -- -- -- 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 ---------------------------------------------- -- 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;