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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) 1992-2011, 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;

      Global_Lock : Boolean := False);

   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 RTS_Lock, Global_Lock should be set to True

   --  if L is a global lock (Single_RTS_Lock, Global_Task_Lock).

   --

   --  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;

      Global_Lock : Boolean := False);

   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.)

   --  For the operation on RTS_Lock, Global_Lock should be set to True if L

   --  is a global lock (Single_RTS_Lock, Global_Task_Lock).

   --

   --  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 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 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. Since we intend these routines to be used

   --  for implementing the Single_Lock RTS, Lock_RTS should follow the first

   --  Defer_Abort operation entering RTS. In the same fashion Unlock_RTS

   --  should precede the last Undefer_Abort exiting 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;