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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 --
-- --
-- Copyright (C) 1992-2021, Free Software Foundation, Inc. --
-- --
-- GNARL is free software; you can redistribute it and/or modify it under --
-- terms of the GNU General Public License as published by the Free Soft- --
-- ware Foundation; either version 3, or (at your option) any later ver- --
-- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
-- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
-- or FITNESS FOR A PARTICULAR PURPOSE. --
-- --
-- As a special exception under Section 7 of GPL version 3, you are granted --
-- additional permissions described in the GCC Runtime Library Exception, --
-- version 3.1, as published by the Free Software Foundation. --
-- --
-- You should have received a copy of the GNU General Public License and --
-- a copy of the GCC Runtime Library Exception along with this program; --
-- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
-- <http://www.gnu.org/licenses/>. --
-- --
-- GNARL was developed by the GNARL team at Florida State University. --
-- Extensive contributions were provided by Ada Core Technologies, Inc. --
-- --
------------------------------------------------------------------------------
-- This package contains all the GNULL primitives that interface directly with
-- the underlying OS.
with System.Parameters;
with System.Tasking;
with System.OS_Interface;
package System.Task_Primitives.Operations is
pragma Preelaborate;
package ST renames System.Tasking;
package OSI renames System.OS_Interface;
procedure Initialize (Environment_Task : ST.Task_Id);
-- Perform initialization and set up of the environment task for proper
-- operation of the tasking run-time. 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 abort 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.
----------------------------------
-- ATCB allocation/deallocation --
----------------------------------
package ATCB_Allocation is
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 Free_ATCB (T : ST.Task_Id);
pragma Inline (Free_ATCB);
-- Deallocate an ATCB previously allocated by New_ATCB
end ATCB_Allocation;
function New_ATCB (Entry_Num : ST.Task_Entry_Index) return ST.Task_Id
renames ATCB_Allocation.New_ATCB;
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,
RTS_Lock_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 : not null access Lock);
procedure Initialize_Lock
(L : not null 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 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 : not null access Lock);
procedure Finalize_Lock (L : not null 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 : not null access Lock;
Ceiling_Violation : out Boolean);
procedure Write_Lock (L : not null 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 : not null 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 : not null access Lock);
procedure Unlock (L : not null 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 would give terrible
-- performance on systems where this has the effect of masking hardware
-- interrupts, though we could get away 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 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 ceiling violation
procedure Set_Ceiling
(L : not null access Lock;
Prio : System.Any_Priority);
pragma Inline (Set_Ceiling);
-- Change the ceiling priority associated to the lock
--
-- 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.)
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. On most platforms, Yield is a no-op if Do_Yield
-- is False. But on some platforms (notably VxWorks), Do_Yield is ignored.
-- This is only used in some very rare cases where 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 Prio. 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 an
-- unspecified Epoch. This clock implementation is immune to the
-- system's clock changes.
function RT_Resolution return Duration;
pragma Inline (RT_Resolution);
-- Returns 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);
-- Implement the semantics of the delay statement.
-- The caller should be abort-deferred and should 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);
-- Return 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;
-- Return the thread id of the specified task
function Is_Valid_Task return Boolean;
pragma Inline (Is_Valid_Task);
-- Does the calling thread have an ATCB?
function Register_Foreign_Thread return ST.Task_Id;
-- Allocate and initialize a new ATCB for the current thread
-----------------------
-- RTS Entrance/Exit --
-----------------------
-- Following two routines are used for possible operations needed to be
-- setup/cleared upon entrance/exit of RTS while maintaining a single
-- thread of control in the RTS.
--
-- These routines also replace the functions Lock/Unlock_All_Tasks_List
procedure Lock_RTS;
-- Take the global RTS lock
procedure Unlock_RTS;
-- Release the global RTS lock
--------------------
-- 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 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.
------------------------
-- Suspension objects --
------------------------
-- These subprograms provide the functionality required for synchronizing
-- on a suspension object. Tasks can suspend execution and relinquish the
-- processors until the condition is signaled.
function Current_State (S : Suspension_Object) return Boolean;
-- Return the state of the suspension object
procedure Set_False (S : in out Suspension_Object);
-- Set the state of the suspension object to False
procedure Set_True (S : in out Suspension_Object);
-- Set the state of the suspension object to True. If a task were
-- suspended on the protected object then this task is released (and
-- the state of the suspension object remains set to False).
procedure Suspend_Until_True (S : in out Suspension_Object);
-- If the state of the suspension object is True then the calling task
-- continues its execution, and the state is set to False. If the state
-- of the object is False then the task is suspended on the suspension
-- object until a Set_True operation is executed. Program_Error is raised
-- if another task is already waiting on that suspension object.
procedure Initialize (S : in out Suspension_Object);
-- Initialize the suspension object
procedure Finalize (S : in out Suspension_Object);
-- Finalize the suspension object
-----------------------------------------
-- 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 this
-- 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. On targets where this operation is not
-- available, a dummy body is present which always returns False.
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 Stop_All_Tasks;
-- Stop all tasks when the underlying thread library provides such
-- functionality. Such functionality is needed by gdb on some targets (e.g
-- VxWorks) This function can be run from an interrupt handler. Return True
-- is the operation is successful
function Stop_Task (T : ST.Task_Id) return Boolean;
-- Stop a specific task when the underlying thread library provides
-- such functionality. Such functionality is needed by gdb on some targets
-- (e.g VxWorks). Return True is the operation is successful.
function Continue_Task (T : ST.Task_Id) return Boolean;
-- Continue a specific task when the underlying thread library provides
-- such functionality. Such functionality is needed by gdb on some targets
-- (e.g VxWorks) Return True is the operation is successful
-------------------
-- Task affinity --
-------------------
procedure Set_Task_Affinity (T : ST.Task_Id);
-- Enforce at the operating system level the task affinity defined in the
-- Ada Task Control Block. Has no effect if the underlying operating system
-- does not support this capability.
end System.Task_Primitives.Operations;