-- --
-- S p e c --
-- --
--- Copyright (C) 1992-2003, Free Software Foundation, Inc. --
+-- Copyright (C) 1992-2004, 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- --
package System.Tasking is
- -- -------------------
- -- -- Locking Rules --
- -- -------------------
- --
+ -------------------
+ -- 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.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.
-- the parent always has a lower serial number than the activator.
---------------------------------
- -- Task_ID related definitions --
+ -- Task_Id related definitions --
---------------------------------
type Ada_Task_Control_Block;
- type Task_ID is access all Ada_Task_Control_Block;
+ type Task_Id is access all Ada_Task_Control_Block;
- Null_Task : constant Task_ID;
+ Null_Task : constant Task_Id;
- type Task_List is array (Positive range <>) of Task_ID;
+ type Task_List is array (Positive range <>) of Task_Id;
- function Self return 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);
+ 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 --
-- async. select statement does not need to lock anything.
type Restricted_Entry_Call_Record is record
- Self : Task_ID;
+ Self : Task_Id;
-- ID of the caller
Mode : Call_Modes;
-- 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.
+ -- 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 --
- -- --
- -- This section is used by all GNARL implementations (regular and --
- -- restricted) --
- ----------------------------------------------------------------------
+ -------------------------
+ -- Common ATCB section --
+ -------------------------
+
+ -- Section used by all GNARL implementations (regular and restricted)
type Common_ATCB is record
State : Task_States;
-- and whether it is terminated.
-- Protection: Self.L.
- Parent : Task_ID;
+ Parent : Task_Id;
-- The task on which this task depends.
-- See also Master_Level and Master_Within.
-- per-task structures.
-- Protection: Only accessed by Self.
- All_Tasks_Link : Task_ID;
+ 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;
+ 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;
+ 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.
end record;
pragma Suppress_Initialization (Restricted_Ada_Task_Control_Block);
- Interrupt_Manager_ID : Task_ID;
+ 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
+ -- 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;
+ All_Tasks_List : Task_Id;
-- Global linked list of all tasks.
------------------------------------------
----------------------------------
type Entry_Call_Record is record
- Self : Task_ID;
+ Self : Task_Id;
-- ID of the caller
Mode : Call_Modes;
-- They are gathered together to allow for compilers that lay records
-- out contiguously, to allow for such packing.
- Called_Task : Task_ID;
+ 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.
------------------------------------
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 --
---------------------
procedure Initialize_ATCB
- (Self_ID : Task_ID;
+ (Self_ID : Task_Id;
Task_Entry_Point : Task_Procedure_Access;
Task_Arg : System.Address;
- Parent : Task_ID;
+ 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;
+ 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 RTS_Lock.
private
- Null_Task : constant Task_ID := null;
+ Null_Task : constant Task_Id := null;
type Activation_Chain is record
- T_ID : Task_ID;
+ T_ID : Task_Id;
end record;
pragma Volatile (Activation_Chain);
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