1------------------------------------------------------------------------------
2--                                                                          --
3--                 GNAT RUN-TIME LIBRARY (GNARL) COMPONENTS                 --
4--                                                                          --
5--               SYSTEM.TASKING.PROTECTED_OBJECTS.SINGLE_ENTRY              --
6--                                                                          --
7--                                  S p e c                                 --
8--                                                                          --
9--          Copyright (C) 1992-2019, Free Software Foundation, Inc.         --
10--                                                                          --
11-- GNAT 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------------------------------------------------------------------------------
31
32--  This package provides an optimized version of Protected_Objects.Operations
33--  and Protected_Objects.Entries making the following assumptions:
34
35--    PO have only one entry
36--    There is only one caller at a time (No_Entry_Queue)
37--    There is no dynamic priority support (No_Dynamic_Priorities)
38--    No Abort Statements
39--      (No_Abort_Statements, Max_Asynchronous_Select_Nesting => 0)
40--    PO are at library level
41--    None of the tasks will terminate (no need for finalization)
42
43--  This interface is intended to be used in the Ravenscar profile, the
44--  compiler is responsible for ensuring that the conditions mentioned above
45--  are respected, except for the No_Entry_Queue restriction that is checked
46--  dynamically in this package, since the check cannot be performed at compile
47--  time, and is relatively cheap (see body).
48
49--  This package is part of the high level tasking interface used by the
50--  compiler to expand Ada 95 tasking constructs into simpler run time calls
51--  (aka GNARLI, GNU Ada Run-time Library Interface)
52
53--  Note: the compiler generates direct calls to this interface, via Rtsfind.
54--  Any changes to this interface may require corresponding compiler changes
55--  in exp_ch9.adb and possibly exp_ch7.adb
56
57package System.Tasking.Protected_Objects.Single_Entry is
58   pragma Elaborate_Body;
59
60   ---------------------------------
61   -- Compiler Interface (GNARLI) --
62   ---------------------------------
63
64   --  The compiler will expand in the GNAT tree the following construct:
65
66   --  protected PO is
67   --     entry E;
68   --     procedure P;
69   --  private
70   --     Open : Boolean := False;
71   --  end PO;
72
73   --  protected body PO is
74   --     entry E when Open is
75   --        ...variable declarations...
76   --     begin
77   --        ...B...
78   --     end E;
79
80   --     procedure P is
81   --        ...variable declarations...
82   --     begin
83   --        ...C...
84   --     end P;
85   --  end PO;
86
87   --  as follows:
88
89   --  protected type poT is
90   --     entry e;
91   --     procedure p;
92   --  private
93   --     open : boolean := false;
94   --  end poT;
95   --  type poTV is limited record
96   --     open : boolean := false;
97   --     _object : aliased protection_entry;
98   --  end record;
99   --  procedure poPT__E1s (O : address; P : address; E :
100   --    protected_entry_index);
101   --  function poPT__B2s (O : address; E : protected_entry_index) return
102   --    boolean;
103   --  procedure poPT__pN (_object : in out poTV);
104   --  procedure poPT__pP (_object : in out poTV);
105   --  poTA : aliased entry_body := (
106   --     barrier => poPT__B2s'unrestricted_access,
107   --     action => poPT__E1s'unrestricted_access);
108   --  freeze poTV [
109   --     procedure poTVIP (_init : in out poTV) is
110   --     begin
111   --        _init.open := false;
112   --        object-init-proc (_init._object);
113   --        initialize_protection_entry (_init._object'unchecked_access,
114   --          unspecified_priority, _init'address, poTA'
115   --          unrestricted_access);
116   --        return;
117   --     end poTVIP;
118   --  ]
119   --  po : poT;
120   --  poTVIP (poTV!(po));
121
122   --  function poPT__B2s (O : address; E : protected_entry_index) return
123   --    boolean is
124   --     type poTVP is access poTV;
125   --     _object : poTVP := poTVP!(O);
126   --     poR : protection_entry renames _object._object;
127   --     openP : boolean renames _object.open;
128   --  begin
129   --     return open;
130   --  end poPT__B2s;
131
132   --  procedure poPT__E1s (O : address; P : address; E :
133   --    protected_entry_index) is
134   --     type poTVP is access poTV;
135   --     _object : poTVP := poTVP!(O);
136   --  begin
137   --     B1b : declare
138   --        poR : protection_entry renames _object._object;
139   --        openP : boolean renames _object.open;
140   --        ...variable declarations...
141   --     begin
142   --        ...B...
143   --     end B1b;
144   --     complete_single_entry_body (_object._object'unchecked_access);
145   --     return;
146   --  exception
147   --     when all others =>
148   --        exceptional_complete_single_entry_body (_object._object'
149   --          unchecked_access, get_gnat_exception);
150   --        return;
151   --  end poPT__E1s;
152
153   --  procedure poPT__pN (_object : in out poTV) is
154   --     poR : protection_entry renames _object._object;
155   --     openP : boolean renames _object.open;
156   --     ...variable declarations...
157   --  begin
158   --     ...C...
159   --     return;
160   --  end poPT__pN;
161
162   --  procedure poPT__pP (_object : in out poTV) is
163   --     procedure _clean is
164   --     begin
165   --        service_entry (_object._object'unchecked_access);
166   --        return;
167   --     end _clean;
168   --  begin
169   --     lock_entry (_object._object'unchecked_access);
170   --     B5b : begin
171   --        poPT__pN (_object);
172   --     at end
173   --        _clean;
174   --     end B5b;
175   --     return;
176   --  end poPT__pP;
177
178   type Protection_Entry is limited private;
179   --  This type contains the GNARL state of a protected object. The
180   --  application-defined portion of the state (i.e. private objects)
181   --  is maintained by the compiler-generated code.
182
183   type Protection_Entry_Access is access all Protection_Entry;
184
185   type Entry_Body_Access is access constant Entry_Body;
186   --  Access to barrier and action function of an entry
187
188   procedure Initialize_Protection_Entry
189     (Object           : Protection_Entry_Access;
190      Ceiling_Priority : Integer;
191      Compiler_Info    : System.Address;
192      Entry_Body       : Entry_Body_Access);
193   --  Initialize the Object parameter so that it can be used by the run time
194   --  to keep track of the runtime state of a protected object.
195
196   procedure Lock_Entry (Object : Protection_Entry_Access);
197   --  Lock a protected object for write access. Upon return, the caller owns
198   --  the lock to this object, and no other call to Lock or Lock_Read_Only
199   --  with the same argument will return until the corresponding call to
200   --  Unlock has been made by the caller.
201
202   procedure Lock_Read_Only_Entry
203     (Object : Protection_Entry_Access);
204   --  Lock a protected object for read access. Upon return, the caller owns
205   --  the lock for read access, and no other calls to Lock with the same
206   --  argument will return until the corresponding call to Unlock has been
207   --  made by the caller. Other calls to Lock_Read_Only may (but need not)
208   --  return before the call to Unlock, and the corresponding callers will
209   --  also own the lock for read access.
210
211   procedure Unlock_Entry (Object : Protection_Entry_Access);
212   --  Relinquish ownership of the lock for the object represented by the
213   --  Object parameter. If this ownership was for write access, or if it was
214   --  for read access where there are no other read access locks outstanding,
215   --  one (or more, in the case of Lock_Read_Only) of the tasks waiting on
216   --  this lock (if any) will be given the lock and allowed to return from
217   --  the Lock or Lock_Read_Only call.
218
219   procedure Service_Entry (Object : Protection_Entry_Access);
220   --  Service the entry queue of the specified object, executing the
221   --  corresponding body of any queued entry call that is waiting on True
222   --  barrier. This is used when the state of a protected object may have
223   --  changed, in particular after the execution of the statement sequence
224   --  of a protected procedure.
225   --
226   --  This must be called with abort deferred and with the corresponding
227   --  object locked. Object is unlocked on return.
228
229   procedure Protected_Single_Entry_Call
230     (Object              : Protection_Entry_Access;
231      Uninterpreted_Data  : System.Address);
232   --  Make a protected entry call to the specified object
233   --
234   --  Pends a protected entry call on the protected object represented by
235   --  Object. A pended call is not queued; it may be executed immediately
236   --  or queued, depending on the state of the entry barrier.
237   --
238   --    Uninterpreted_Data
239   --      This will be returned by Next_Entry_Call when this call is serviced.
240   --      It can be used by the compiler to pass information between the
241   --      caller and the server, in particular entry parameters.
242
243   procedure Exceptional_Complete_Single_Entry_Body
244     (Object : Protection_Entry_Access;
245      Ex     : Ada.Exceptions.Exception_Id);
246   --  Perform all of the functions of Complete_Entry_Body. In addition, report
247   --  in Ex the exception whose propagation terminated the entry body to the
248   --  runtime system.
249
250   function Protected_Count_Entry (Object : Protection_Entry) return Natural;
251   --  Return the number of entry calls on Object (0 or 1)
252
253   function Protected_Single_Entry_Caller
254     (Object : Protection_Entry) return Task_Id;
255   --  Return value of E'Caller, where E is the protected entry currently being
256   --  handled. This will only work if called from within an entry body, as
257   --  required by the LRM (C.7.1(14)).
258
259private
260   type Protection_Entry is record
261      Common : aliased Protection;
262      --  State of the protected object. This part is common to any protected
263      --  object, including those without entries.
264
265      Compiler_Info : System.Address;
266      --  Pointer to compiler-generated record representing protected object
267
268      Call_In_Progress : Entry_Call_Link;
269      --  Pointer to the entry call being executed (if any)
270
271      Entry_Body : Entry_Body_Access;
272      --  Pointer to executable code for the entry body of the protected type
273
274      Entry_Queue : Entry_Call_Link;
275      --  Place to store the waiting entry call (if any)
276   end record;
277
278end System.Tasking.Protected_Objects.Single_Entry;
279