+++ /dev/null
-------------------------------------------------------------------------------
--- --
--- 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: 1.3.10.1 $
--- --
--- 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. --
--- 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;
--- 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;