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8sa1-gcc/gcc/ada/s-taprop.ads
Robert Dewar f5e44987a6 lib.adb: Minor reformatting 
* lib.adb: Minor reformatting

	* s-taprop.ads: Minor reformatting

From-SVN: r46651
2001-10-30 21:56:09 +01:00

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------------------------------------------------------------------------------
-- --
-- GNU ADA RUN-TIME LIBRARY (GNARL) COMPONENTS --
-- --
-- S Y S T E M . T A S K _ P R I M I T I V E S .O P E R A T I O N S --
-- --
-- S p e c --
-- --
-- $Revision$
-- --
-- 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 contains all the GNULL primitives that interface directly
-- with the underlying OS.
with System.Parameters;
-- used for Size_Type
with System.Tasking;
-- used for Task_ID
with System.OS_Interface;
-- used for Thread_Id
package System.Task_Primitives.Operations is
pragma Elaborate_Body;
package ST renames System.Tasking;
package OSI renames System.OS_Interface;
procedure Initialize (Environment_Task : ST.Task_ID);
pragma Inline (Initialize);
-- This must be called once, before any other subprograms of this
-- package are called.
procedure Create_Task
(T : ST.Task_ID;
Wrapper : System.Address;
Stack_Size : System.Parameters.Size_Type;
Priority : System.Any_Priority;
Succeeded : out Boolean);
pragma Inline (Create_Task);
-- Create a new low-level task with ST.Task_ID T and place other needed
-- information in the ATCB.
--
-- A new thread of control is created, with a stack of at least Stack_Size
-- storage units, and the procedure Wrapper is called by this new thread
-- of control. If Stack_Size = Unspecified_Storage_Size, choose a default
-- stack size; this may be effectively "unbounded" on some systems.
--
-- The newly created low-level task is associated with the ST.Task_ID T
-- such that any subsequent call to Self from within the context of the
-- low-level task returns T.
--
-- The caller is responsible for ensuring that the storage of the Ada
-- task control block object pointed to by T persists for the lifetime
-- of the new task.
--
-- Succeeded is set to true unless creation of the task failed,
-- as it may if there are insufficient resources to create another task.
procedure Enter_Task (Self_ID : ST.Task_ID);
pragma Inline (Enter_Task);
-- Initialize data structures specific to the calling task.
-- Self must be the ID of the calling task.
-- It must be called (once) by the task immediately after creation,
-- while abortion is still deferred.
-- The effects of other operations defined below are not defined
-- unless the caller has previously called Initialize_Task.
procedure Exit_Task;
pragma Inline (Exit_Task);
-- Destroy the thread of control.
-- Self must be the ID of the calling task.
-- The effects of further calls to operations defined below
-- on the task are undefined thereafter.
function New_ATCB (Entry_Num : ST.Task_Entry_Index) return ST.Task_ID;
pragma Inline (New_ATCB);
-- Allocate a new ATCB with the specified number of entries.
procedure Initialize_TCB (Self_ID : ST.Task_ID; Succeeded : out Boolean);
pragma Inline (Initialize_TCB);
-- Initialize all fields of the TCB
procedure Finalize_TCB (T : ST.Task_ID);
pragma Inline (Finalize_TCB);
-- Finalizes Private_Data of ATCB, and then deallocates it.
-- This is also responsible for recovering any storage or other resources
-- that were allocated by Create_Task (the one in this package).
-- This should only be called from Free_Task.
-- After it is called there should be no further
-- reference to the ATCB that corresponds to T.
procedure Abort_Task (T : ST.Task_ID);
pragma Inline (Abort_Task);
-- Abort the task specified by T (the target task). This causes
-- the target task to asynchronously raise Abort_Signal if
-- abort is not deferred, or if it is blocked on an interruptible
-- system call.
--
-- precondition:
-- the calling task is holding T's lock and has abort deferred
--
-- postcondition:
-- the calling task is holding T's lock and has abort deferred.
-- ??? modify GNARL to skip wakeup and always call Abort_Task
function Self return ST.Task_ID;
pragma Inline (Self);
-- Return a pointer to the Ada Task Control Block of the calling task.
type Lock_Level is
(PO_Level,
Global_Task_Level,
All_Attrs_Level,
All_Tasks_Level,
Interrupts_Level,
ATCB_Level);
-- Type used to describe kind of lock for second form of Initialize_Lock
-- call specified below.
-- See locking rules in System.Tasking (spec) for more details.
procedure Initialize_Lock (Prio : System.Any_Priority; L : access Lock);
procedure Initialize_Lock (L : access RTS_Lock; Level : Lock_Level);
pragma Inline (Initialize_Lock);
-- Initialize a lock object.
--
-- For Lock, Prio is the ceiling priority associated with the lock.
-- For RTS_Lock, the ceiling is implicitly Priority'Last.
--
-- If the underlying system does not support priority ceiling
-- locking, the Prio parameter is ignored.
--
-- The effect of either initialize operation is undefined unless L
-- is a lock object that has not been initialized, or which has been
-- finalized since it was last initialized.
--
-- The effects of the other operations on lock objects
-- are undefined unless the lock object has been initialized
-- and has not since been finalized.
--
-- Initialization of the per-task lock is implicit in Create_Task.
--
-- These operations raise Storage_Error if a lack of storage is detected.
procedure Finalize_Lock (L : access Lock);
procedure Finalize_Lock (L : access RTS_Lock);
pragma Inline (Finalize_Lock);
-- Finalize a lock object, freeing any resources allocated by the
-- corresponding Initialize_Lock operation.
procedure Write_Lock (L : access Lock; Ceiling_Violation : out Boolean);
procedure Write_Lock (L : access RTS_Lock);
procedure Write_Lock (T : ST.Task_ID);
pragma Inline (Write_Lock);
-- Lock a lock object for write access. After this operation returns,
-- the calling task holds write permission for the lock object. No other
-- Write_Lock or Read_Lock operation on the same lock object will return
-- until this task executes an Unlock operation on the same object. The
-- effect is undefined if the calling task already holds read or write
-- permission for the lock object L.
--
-- For the operation on Lock, Ceiling_Violation is set to true iff the
-- operation failed, which will happen if there is a priority ceiling
-- violation.
--
-- For the operation on ST.Task_ID, the lock is the special lock object
-- associated with that task's ATCB. This lock has effective ceiling
-- priority high enough that it is safe to call by a task with any
-- priority in the range System.Priority. It is implicitly initialized
-- by task creation. The effect is undefined if the calling task already
-- holds T's lock, or has interrupt-level priority. Finalization of the
-- per-task lock is implicit in Exit_Task.
procedure Read_Lock (L : access Lock; Ceiling_Violation : out Boolean);
pragma Inline (Read_Lock);
-- Lock a lock object for read access. After this operation returns,
-- the calling task has non-exclusive read permission for the logical
-- resources that are protected by the lock. No other Write_Lock operation
-- on the same object will return until this task and any other tasks with
-- read permission for this lock have executed Unlock operation(s) on the
-- lock object. A Read_Lock for a lock object may return immediately while
-- there are tasks holding read permission, provided there are no tasks
-- holding write permission for the object. The effect is undefined if
-- the calling task already holds read or write permission for L.
--
-- Alternatively: An implementation may treat Read_Lock identically to
-- Write_Lock. This simplifies the implementation, but reduces the level
-- of concurrency that can be achieved.
--
-- Note that Read_Lock is not defined for RT_Lock and ST.Task_ID.
-- That is because (1) so far Read_Lock has always been implemented
-- the same as Write_Lock, (2) most lock usage inside the RTS involves
-- potential write access, and (3) implementations of priority ceiling
-- locking that make a reader-writer distinction have higher overhead.
procedure Unlock (L : access Lock);
procedure Unlock (L : access RTS_Lock);
procedure Unlock (T : ST.Task_ID);
pragma Inline (Unlock);
-- Unlock a locked lock object.
--
-- The effect is undefined unless the calling task holds read or write
-- permission for the lock L, and L is the lock object most recently
-- locked by the calling task for which the calling task still holds
-- read or write permission. (That is, matching pairs of Lock and Unlock
-- operations on each lock object must be properly nested.)
-- Note that Write_Lock for RTS_Lock does not have an out-parameter.
-- RTS_Locks are used in situations where we have not made provision
-- for recovery from ceiling violations. We do not expect them to
-- occur inside the runtime system, because all RTS locks have ceiling
-- Priority'Last.
-- There is one way there can be a ceiling violation.
-- That is if the runtime system is called from a task that is
-- executing in the Interrupt_Priority range.
-- It is not clear what to do about ceiling violations due
-- to RTS calls done at interrupt priority. In general, it
-- is not acceptable to give all RTS locks interrupt priority,
-- since that whould give terrible performance on systems where
-- this has the effect of masking hardware interrupts, though we
-- could get away with allowing Interrupt_Priority'last where we
-- are layered on an OS that does not allow us to mask interrupts.
-- Ideally, we would like to raise Program_Error back at the
-- original point of the RTS call, but this would require a lot of
-- detailed analysis and recoding, with almost certain performance
-- penalties.
-- For POSIX systems, we considered just skipping setting a
-- priority ceiling on RTS locks. This would mean there is no
-- ceiling violation, but we would end up with priority inversions
-- inside the runtime system, resulting in failure to satisfy the
-- Ada priority rules, and possible missed validation tests.
-- This could be compensated-for by explicit priority-change calls
-- to raise the caller to Priority'Last whenever it first enters
-- the runtime system, but the expected overhead seems high, though
-- it might be lower than using locks with ceilings if the underlying
-- implementation of ceiling locks is an inefficient one.
-- This issue should be reconsidered whenever we get around to
-- checking for calls to potentially blocking operations from
-- within protected operations. If we check for such calls and
-- catch them on entry to the OS, it may be that we can eliminate
-- the possibility of ceiling violations inside the RTS. For this
-- to work, we would have to forbid explicitly setting the priority
-- of a task to anything in the Interrupt_Priority range, at least.
-- We would also have to check that there are no RTS-lock operations
-- done inside any operations that are not treated as potentially
-- blocking.
-- The latter approach seems to be the best, i.e. to check on entry
-- to RTS calls that may need to use locks that the priority is not
-- in the interrupt range. If there are RTS operations that NEED to
-- be called from interrupt handlers, those few RTS locks should then
-- be converted to PO-type locks, with ceiling Interrupt_Priority'Last.
-- For now, we will just shut down the system if there is a
-- ceiling violation.
procedure Yield (Do_Yield : Boolean := True);
pragma Inline (Yield);
-- Yield the processor. Add the calling task to the tail of the
-- ready queue for its active_priority.
-- The Do_Yield argument is only used in some very rare cases very
-- a yield should have an effect on a specific target and not on regular
-- ones.
procedure Set_Priority
(T : ST.Task_ID;
Prio : System.Any_Priority;
Loss_Of_Inheritance : Boolean := False);
pragma Inline (Set_Priority);
-- Set the priority of the task specified by T to T.Current_Priority.
-- The priority set is what would correspond to the Ada concept of
-- "base priority" in the terms of the lower layer system, but
-- the operation may be used by the upper layer to implement
-- changes in "active priority" that are not due to lock effects.
-- The effect should be consistent with the Ada Reference Manual.
-- In particular, when a task lowers its priority due to the loss of
-- inherited priority, it goes at the head of the queue for its new
-- priority (RM D.2.2 par 9).
-- Loss_Of_Inheritance helps the underlying implementation to do it
-- right when the OS doesn't.
function Get_Priority (T : ST.Task_ID) return System.Any_Priority;
pragma Inline (Get_Priority);
-- Returns the priority last set by Set_Priority for this task.
function Monotonic_Clock return Duration;
pragma Inline (Monotonic_Clock);
-- Returns "absolute" time, represented as an offset
-- relative to "the Epoch", which is Jan 1, 1970.
-- This clock implementation is immune to the system's clock changes.
function RT_Resolution return Duration;
pragma Inline (RT_Resolution);
-- Returns the resolution of the underlying clock used to implement
-- RT_Clock.
------------------
-- Extensions --
------------------
-- Whoever calls either of the Sleep routines is responsible
-- for checking for pending aborts before the call.
-- Pending priority changes are handled internally.
procedure Sleep
(Self_ID : ST.Task_ID;
Reason : System.Tasking.Task_States);
pragma Inline (Sleep);
-- Wait until the current task, T, is signaled to wake up.
--
-- precondition:
-- The calling task is holding its own ATCB lock
-- and has abort deferred
--
-- postcondition:
-- The calling task is holding its own ATCB lock
-- and has abort deferred.
-- The effect is to atomically unlock T's lock and wait, so that another
-- task that is able to lock T's lock can be assured that the wait has
-- actually commenced, and that a Wakeup operation will cause the waiting
-- task to become ready for execution once again. When Sleep returns,
-- the waiting task will again hold its own ATCB lock. The waiting task
-- may become ready for execution at any time (that is, spurious wakeups
-- are permitted), but it will definitely become ready for execution when
-- a Wakeup operation is performed for the same task.
procedure Timed_Sleep
(Self_ID : ST.Task_ID;
Time : Duration;
Mode : ST.Delay_Modes;
Reason : System.Tasking.Task_States;
Timedout : out Boolean;
Yielded : out Boolean);
-- Combination of Sleep (above) and Timed_Delay
procedure Timed_Delay
(Self_ID : ST.Task_ID;
Time : Duration;
Mode : ST.Delay_Modes);
-- Implements the semantics of the delay statement. It is assumed that
-- the caller is not abort-deferred and does not hold any locks.
procedure Wakeup
(T : ST.Task_ID;
Reason : System.Tasking.Task_States);
pragma Inline (Wakeup);
-- Wake up task T if it is waiting on a Sleep call (of ordinary
-- or timed variety), making it ready for execution once again.
-- If the task T is not waiting on a Sleep, the operation has no effect.
function Environment_Task return ST.Task_ID;
pragma Inline (Environment_Task);
-- returns the task ID of the environment task
-- Consider putting this into a variable visible directly
-- by the rest of the runtime system. ???
function Get_Thread_Id (T : ST.Task_ID) return OSI.Thread_Id;
-- returns the thread id of the specified task.
--------------------
-- Stack Checking --
--------------------
-- Stack checking in GNAT is done using the concept of stack probes. A
-- stack probe is an operation that will generate a storage error if
-- an insufficient amount of stack space remains in the current task.
-- The exact mechanism for a stack probe is target dependent. Typical
-- possibilities are to use a load from a non-existent page, a store
-- to a read-only page, or a comparison with some stack limit constant.
-- Where possible we prefer to use a trap on a bad page access, since
-- this has less overhead. The generation of stack probes is either
-- automatic if the ABI requires it (as on for example DEC Unix), or
-- is controlled by the gcc parameter -fstack-check.
-- When we are using bad-page accesses, we need a bad page, called a
-- guard page, at the end of each task stack. On some systems, this
-- is provided automatically, but on other systems, we need to create
-- the guard page ourselves, and the procedure Stack_Guard is provided
-- for this purpose.
procedure Stack_Guard (T : ST.Task_ID; On : Boolean);
-- Ensure guard page is set if one is needed and the underlying thread
-- system does not provide it. The procedure is as follows:
--
-- 1. When we create a task adjust its size so a guard page can
-- safely be set at the bottom of the stack
--
-- 2. When the thread is created (and its stack allocated by the
-- underlying thread system), get the stack base (and size, depending
-- how the stack is growing), and create the guard page taking care of
-- page boundaries issues.
--
-- 3. When the task is destroyed, remove the guard page.
--
-- If On is true then protect the stack bottom (i.e make it read only)
-- else unprotect it (i.e. On is True for the call when creating a task,
-- and False when a task is destroyed).
--
-- The call to Stack_Guard has no effect if guard pages are not used on
-- the target, or if guard pages are automatically provided by the system.
-----------------------------------------
-- Runtime System Debugging Interfaces --
-----------------------------------------
-- These interfaces have been added to assist in debugging the
-- tasking runtime system.
function Check_Exit (Self_ID : ST.Task_ID) return Boolean;
pragma Inline (Check_Exit);
-- Check that the current task is holding only Global_Task_Lock.
function Check_No_Locks (Self_ID : ST.Task_ID) return Boolean;
pragma Inline (Check_No_Locks);
-- Check that current task is holding no locks.
function Suspend_Task
(T : ST.Task_ID;
Thread_Self : OSI.Thread_Id)
return Boolean;
-- Suspend a specific task when the underlying thread library provides
-- such functionality, unless the thread associated with T is Thread_Self.
-- Such functionality is needed by gdb on some targets (e.g VxWorks)
-- Return True is the operation is successful
function Resume_Task
(T : ST.Task_ID;
Thread_Self : OSI.Thread_Id)
return Boolean;
-- Resume a specific task when the underlying thread library provides
-- such functionality, unless the thread associated with T is Thread_Self.
-- Such functionality is needed by gdb on some targets (e.g VxWorks)
-- Return True is the operation is successful
procedure Lock_All_Tasks_List;
procedure Unlock_All_Tasks_List;
-- Lock/Unlock the All_Tasks_L lock which protects
-- System.Initialization.All_Tasks_List and Known_Tasks
-- ??? These routines were previousely in System.Tasking.Initialization
-- but were moved here to avoid dependency problems. That would be
-- nice to look at it some day and put it back in Initialization.
end System.Task_Primitives.Operations;
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