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1 ------------------------------------------------------------------------------
2 -- --
3 -- GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS --
4 -- --
5 -- S Y S T E M . T A S K I N G . S T A G E S --
6 -- --
7 -- S p e c --
8 -- --
9 -- Copyright (C) 1992-2018, Free Software Foundation, Inc. --
10 -- --
11 -- GNARL is free software; you can redistribute it and/or modify it under --
12 -- terms of the GNU General Public License as published by the Free Soft- --
13 -- ware Foundation; either version 3, or (at your option) any later ver- --
14 -- sion. GNAT is distributed in the hope that it will be useful, but WITH- --
15 -- OUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY --
16 -- or FITNESS FOR A PARTICULAR PURPOSE. --
17 -- --
18 -- As a special exception under Section 7 of GPL version 3, you are granted --
19 -- additional permissions described in the GCC Runtime Library Exception, --
20 -- version 3.1, as published by the Free Software Foundation. --
21 -- --
22 -- You should have received a copy of the GNU General Public License and --
23 -- a copy of the GCC Runtime Library Exception along with this program; --
24 -- see the files COPYING3 and COPYING.RUNTIME respectively. If not, see --
25 -- <http://www.gnu.org/licenses/>. --
26 -- --
27 -- GNARL was developed by the GNARL team at Florida State University. --
28 -- Extensive contributions were provided by Ada Core Technologies, Inc. --
29 -- --
30 ------------------------------------------------------------------------------
32 -- This package represents the high level tasking interface used by the
33 -- compiler to expand Ada 95 tasking constructs into simpler run time calls
34 -- (aka GNARLI, GNU Ada Run-time Library Interface)
36 -- Note: Only the compiler is allowed to use this interface, by generating
37 -- direct calls to it, via Rtsfind.
39 -- Any changes to this interface may require corresponding compiler changes
40 -- in exp_ch9.adb and possibly exp_ch7.adb
50 -- The compiler will expand in the GNAT tree the following construct:
52 -- task type T (Discr : Integer);
54 -- task body T is
55 -- ...declarations, possibly some controlled...
56 -- begin
57 -- ...B...;
58 -- end T;
60 -- T1 : T (1);
62 -- as follows:
64 -- enter_master.all;
66 -- _chain : aliased activation_chain;
67 -- activation_chainIP (_chain);
69 -- task type t (discr : integer);
70 -- tE : aliased boolean := false;
71 -- tZ : size_type := unspecified_size;
72 -- type tV (discr : integer) is limited record
73 -- _task_id : task_id;
74 -- end record;
75 -- procedure tB (_task : access tV);
76 -- freeze tV [
77 -- procedure tVIP (_init : in out tV; _master : master_id;
78 -- _chain : in out activation_chain; _task_id : in task_image_type;
79 -- discr : integer) is
80 -- begin
81 -- _init.discr := discr;
82 -- _init._task_id := null;
83 -- create_task (unspecified_priority, tZ,
84 -- unspecified_task_info, unspecified_cpu,
85 -- ada__real_time__time_span_zero, 0, _master,
86 -- task_procedure_access!(tB'address), _init'address,
87 -- tE'unchecked_access, _chain, _task_id, _init._task_id);
88 -- return;
89 -- end tVIP;
90 -- ]
92 -- procedure tB (_task : access tV) is
93 -- discr : integer renames _task.discr;
95 -- procedure _clean is
96 -- begin
97 -- abort_defer.all;
98 -- complete_task;
99 -- finalize_list (F14b);
100 -- abort_undefer.all;
101 -- return;
102 -- end _clean;
103 -- begin
104 -- abort_undefer.all;
105 -- ...declarations...
106 -- complete_activation;
107 -- ...B...;
108 -- return;
109 -- at end
110 -- _clean;
111 -- end tB;
113 -- tE := true;
114 -- t1 : t (1);
115 -- _master : constant master_id := current_master.all;
116 -- t1S : task_image_type := new string'"t1";
117 -- task_image_typeIP (t1, _master, _chain, t1S, 1);
119 -- activate_tasks (_chain'unchecked_access);
122 -- Compiler interface only. Do not call from within the RTS. Initiate
123 -- abort, however, the actual abort is done by abortee by means of
124 -- Abort_Handler and Abort_Undefer
125 --
126 -- source code:
127 -- Abort T1, T2;
128 -- code expansion:
129 -- abort_tasks (task_list'(t1._task_id, t2._task_id));
132 -- Compiler interface only. Do not call from within the RTS.
133 -- This must be called by the creator of a chain of one or more new tasks,
134 -- to activate them. The chain is a linked list that up to this point is
135 -- only known to the task that created them, though the individual tasks
136 -- are already in the All_Tasks_List.
137 --
138 -- The compiler builds the chain in LIFO order (as a stack). Another
139 -- version of this procedure had code to reverse the chain, so as to
140 -- activate the tasks in the order of declaration. This might be nice, but
141 -- it is not needed if priority-based scheduling is supported, since all
142 -- the activated tasks synchronize on the activators lock before they
143 -- start activating and so they should start activating in priority order.
144 -- ??? Actually, the body of this package DOES reverse the chain, so I
145 -- don't understand the above comment.
148 -- Compiler interface only. Do not call from within the RTS.
149 -- This should be called from the task body at the end of
150 -- the elaboration code for its declarative part.
151 -- Decrement the count of tasks to be activated by the activator and
152 -- wake it up so it can check to see if all tasks have been activated.
153 -- Except for the environment task, which should never call this procedure,
154 -- T.Activator should only be null iff T has completed activation.
157 -- Compiler interface only. Do not call from within the RTS. This must
158 -- be called on exit from any master where Enter_Master was called.
159 -- Assume abort is deferred at this point.
162 -- Compiler interface only. Do not call from within the RTS.
163 -- This should be called from an implicit at-end handler
164 -- associated with the task body, when it completes.
165 -- From this point, the current task will become not callable.
166 -- If the current task have not completed activation, this should be done
167 -- now in order to wake up the activator (the environment task).
169 procedure Create_Task
185 -- Compiler interface only. Do not call from within the RTS.
186 -- This must be called to create a new task.
187 --
188 -- Priority is the task's priority (assumed to be in range of type
189 -- System.Any_Priority)
190 --
191 -- Stack_Size is the stack size of the task to create
192 --
193 -- Secondary_Stack_Size is the size of the secondary stack to be used by
194 -- the task.
195 --
196 -- Task_Info is the task info associated with the created task, or
197 -- Unspecified_Task_Info if none.
198 --
199 -- CPU is the task affinity. Passed as an Integer because the undefined
200 -- value is not in the range of CPU_Range. Static range checks are
201 -- performed when analyzing the pragma, and dynamic ones are performed
202 -- before setting the affinity at run time.
203 --
204 -- Relative_Deadline is the relative deadline associated with the created
205 -- task by means of a pragma Relative_Deadline, or 0.0 if none.
206 --
207 -- Domain is the dispatching domain associated with the created task by
208 -- means of a Dispatching_Domain pragma or aspect, or null if none.
209 --
210 -- State is the compiler generated task's procedure body
211 --
212 -- Discriminants is a pointer to a limited record whose discriminants
213 -- are those of the task to create. This parameter should be passed as
214 -- the single argument to State.
215 --
216 -- Elaborated is a pointer to a Boolean that must be set to true on exit
217 -- if the task could be successfully elaborated.
218 --
219 -- Chain is a linked list of task that needs to be created. On exit,
220 -- Created_Task.Activation_Link will be Chain.T_ID, and Chain.T_ID
221 -- will be Created_Task (e.g the created task will be linked at the front
222 -- of Chain).
223 --
224 -- Task_Image is a string created by the compiler that the
225 -- run time can store to ease the debugging and the
226 -- Ada.Task_Identification facility.
227 --
228 -- Created_Task is the resulting task.
229 --
230 -- This procedure can raise Storage_Error if the task creation failed.
233 -- Compiler interface only.
234 -- This is called to obtain the current master nesting level.
237 -- Compiler interface only. Do not call from within the RTS.
238 -- This must be called on entry to any "master" where a task,
239 -- or access type designating objects containing tasks, may be
240 -- declared.
243 -- Compiler interface only. Do not call from within the RTS.
244 -- This must be called by the compiler-generated code for an allocator if
245 -- the allocated object contains tasks, if the allocator exits without
246 -- calling Activate_Tasks for a given activation chains, as can happen if
247 -- an exception occurs during initialization of the object.
248 --
249 -- This should be called ONLY for tasks created via an allocator. Recovery
250 -- of storage for unactivated local task declarations is done by
251 -- Complete_Master and Complete_Task.
252 --
253 -- We remove each task from Chain and All_Tasks_List before we free the
254 -- storage of its ATCB.
255 --
256 -- In other places where we recover the storage of unactivated tasks, we
257 -- need to clean out the entry queues, but here that should not be
258 -- necessary, since these tasks should not have been visible to any other
259 -- tasks, and so no task should be able to queue a call on their entries.
260 --
261 -- Just in case somebody misuses this subprogram, there is a check to
262 -- verify this condition.
265 -- This should be called to complete the execution of the environment task
266 -- and shut down the tasking runtime system. It is the equivalent of
267 -- Complete_Task, but for the environment task.
268 --
269 -- The environment task must first call Complete_Master, to wait for user
270 -- tasks that depend on library-level packages to terminate. It then calls
271 -- Abort_Dependents to abort the "independent" library-level server tasks
272 -- that are created implicitly by the RTS packages (signal and timer server
273 -- tasks), and then waits for them to terminate. Then, it calls
274 -- Vulnerable_Complete_Task.
275 --
276 -- It currently also executes the global finalization list, and then resets
277 -- the "soft links".
280 -- Recover all runtime system storage associated with the task T, but only
281 -- if T has terminated. Do nothing in the other case. It is called from
282 -- Unchecked_Deallocation, for objects that are or contain tasks.
284 procedure Move_Activation_Chain
287 -- Compiler interface only. Do not call from within the RTS.
288 -- Move all tasks on From list to To list, and change their Master_Of_Task
289 -- to be New_Master. This is used to implement build-in-place function
290 -- returns. Tasks that are part of the return object are initially placed
291 -- on an activation chain local to the return statement, and their master
292 -- is the return statement, in case the return statement is left
293 -- prematurely (due to raising an exception, being aborted, or a goto or
294 -- exit statement). Once the return statement has completed successfully,
295 -- Move_Activation_Chain is called to move them to the caller's activation
296 -- chain, and change their master to the one passed in by the caller. If
297 -- that doesn't happen, they will never be activated, and will become
298 -- terminated on leaving the return statement.
301 -- This is called by the compiler to implement the 'Terminated attribute.
302 -- Though is not required to be so by the ARM, we choose to synchronize
303 -- with the task's ATCB, so that this is more useful for polling the state
304 -- of a task, and so that it becomes an abort completion point for the
305 -- calling task (via Undefer_Abort).
306 --
307 -- source code:
308 -- T1'Terminated
309 --
310 -- code expansion:
311 -- terminated (t1._task_id)
314 -- Terminate the calling task.
315 -- This should only be called by the Task_Wrapper procedure, and to
316 -- deallocate storage associate with foreign tasks.