File : g-stsifd-sockets.adb
1 ------------------------------------------------------------------------------
2 -- --
3 -- GNAT COMPILER COMPONENTS --
4 -- --
5 -- G N A T . S O C K E T S . T H I N . S I G N A L L I N G _ F D S --
6 -- --
7 -- B o d y --
8 -- --
9 -- Copyright (C) 2001-2010, AdaCore --
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 -- --
19 -- --
20 -- --
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 -- GNAT was originally developed by the GNAT team at New York University. --
28 -- Extensive contributions were provided by Ada Core Technologies Inc. --
29 -- --
30 ------------------------------------------------------------------------------
31
32 -- Portable sockets-based implementation of GNAT.Sockets.Thin.Signalling_Fds
33 -- used for platforms that do not support UNIX pipes.
34
35 -- Note: this code used to be in GNAT.Sockets, but has been moved to a
36 -- platform-specific file. It is now used only for non-UNIX platforms.
37
38 separate (GNAT.Sockets.Thin)
39 package body Signalling_Fds is
40
41 -----------
42 -- Close --
43 -----------
44
45 procedure Close (Sig : C.int) is
46 Res : C.int;
47 pragma Unreferenced (Res);
48 -- Res is assigned but never read, because we purposefully ignore
49 -- any error returned by the C_Close system call, as per the spec
50 -- of this procedure.
51 begin
52 Res := C_Close (Sig);
53 end Close;
54
55 ------------
56 -- Create --
57 ------------
58
59 function Create (Fds : not null access Fd_Pair) return C.int is
60 L_Sock, R_Sock, W_Sock : C.int := Failure;
61 -- Listening socket, read socket and write socket
62
63 Sin : aliased Sockaddr_In;
64 Len : aliased C.int;
65 -- Address of listening socket
66
67 Res : C.int;
68 pragma Warnings (Off, Res);
69 -- Return status of system calls (usually ignored, hence warnings off)
70
71 begin
72 Fds.all := (Read_End | Write_End => Failure);
73
74 -- We open two signalling sockets. One of them is used to send data
75 -- to the other, which is included in a C_Select socket set. The
76 -- communication is used to force the call to C_Select to complete,
77 -- and the waiting task to resume its execution.
78
79 loop
80 -- Retry loop, in case the C_Connect below fails
81
82 -- Create a listening socket
83
84 L_Sock := C_Socket (SOSC.AF_INET, SOSC.SOCK_STREAM, 0);
85
86 if L_Sock = Failure then
87 goto Fail;
88 end if;
89
90 -- Bind the socket to an available port on localhost
91
92 Set_Family (Sin.Sin_Family, Family_Inet);
93 Sin.Sin_Addr.S_B1 := 127;
94 Sin.Sin_Addr.S_B2 := 0;
95 Sin.Sin_Addr.S_B3 := 0;
96 Sin.Sin_Addr.S_B4 := 1;
97 Sin.Sin_Port := 0;
98
99 Len := C.int (Lengths (Family_Inet));
100 Res := C_Bind (L_Sock, Sin'Address, Len);
101
102 if Res = Failure then
103 goto Fail;
104 end if;
105
106 -- Get assigned port
107
108 Res := C_Getsockname (L_Sock, Sin'Address, Len'Access);
109 if Res = Failure then
110 goto Fail;
111 end if;
112
113 -- Set socket to listen mode, with a backlog of 1 to guarantee that
114 -- exactly one call to connect(2) succeeds.
115
116 Res := C_Listen (L_Sock, 1);
117
118 if Res = Failure then
119 goto Fail;
120 end if;
121
122 -- Create read end (client) socket
123
124 R_Sock := C_Socket (SOSC.AF_INET, SOSC.SOCK_STREAM, 0);
125
126 if R_Sock = Failure then
127 goto Fail;
128 end if;
129
130 -- Connect listening socket
131
132 Res := C_Connect (R_Sock, Sin'Address, Len);
133
134 exit when Res /= Failure;
135
136 if Socket_Errno /= SOSC.EADDRINUSE then
137 goto Fail;
138 end if;
139
140 -- In rare cases, the above C_Bind chooses a port that is still
141 -- marked "in use", even though it has been closed (perhaps by some
142 -- other process that has already exited). This causes the above
143 -- C_Connect to fail with EADDRINUSE. In this case, we close the
144 -- ports, and loop back to try again. This mysterious Windows
145 -- behavior is documented. See, for example:
146 -- http://msdn2.microsoft.com/en-us/library/ms737625.aspx
147 -- In an experiment with 2000 calls, 21 required exactly one retry, 7
148 -- required two, and none required three or more. Note that no delay
149 -- is needed between retries; retrying C_Bind will typically produce
150 -- a different port.
151
152 pragma Assert (Res = Failure
153 and then
154 Socket_Errno = SOSC.EADDRINUSE);
155 Res := C_Close (W_Sock);
156 W_Sock := Failure;
157 Res := C_Close (R_Sock);
158 R_Sock := Failure;
159 end loop;
160
161 -- Since the call to connect(2) has succeeded and the backlog limit on
162 -- the listening socket is 1, we know that there is now exactly one
163 -- pending connection on L_Sock, which is the one from R_Sock.
164
165 W_Sock := C_Accept (L_Sock, Sin'Address, Len'Access);
166
167 if W_Sock = Failure then
168 goto Fail;
169 end if;
170
171 -- Set TCP_NODELAY on W_Sock, since we always want to send the data out
172 -- immediately.
173
174 Set_Socket_Option
175 (Socket => Socket_Type (W_Sock),
176 Level => IP_Protocol_For_TCP_Level,
177 Option => (Name => No_Delay, Enabled => True));
178
179 -- Close listening socket (ignore exit status)
180
181 Res := C_Close (L_Sock);
182
183 Fds.all := (Read_End => R_Sock, Write_End => W_Sock);
184
185 return Thin_Common.Success;
186
187 <<Fail>>
188 declare
189 Saved_Errno : constant Integer := Socket_Errno;
190
191 begin
192 if W_Sock /= Failure then
193 Res := C_Close (W_Sock);
194 end if;
195
196 if R_Sock /= Failure then
197 Res := C_Close (R_Sock);
198 end if;
199
200 if L_Sock /= Failure then
201 Res := C_Close (L_Sock);
202 end if;
203
204 Set_Socket_Errno (Saved_Errno);
205 end;
206
207 return Failure;
208 end Create;
209
210 ----------
211 -- Read --
212 ----------
213
214 function Read (Rsig : C.int) return C.int is
215 Buf : aliased Character;
216 begin
217 return C_Recv (Rsig, Buf'Address, 1, SOSC.MSG_Forced_Flags);
218 end Read;
219
220 -----------
221 -- Write --
222 -----------
223
224 function Write (Wsig : C.int) return C.int is
225 Buf : aliased Character := ASCII.NUL;
226 begin
227 return C_Sendto
228 (Wsig, Buf'Address, 1,
229 Flags => SOSC.MSG_Forced_Flags,
230 To => System.Null_Address,
231 Tolen => 0);
232 end Write;
233
234 end Signalling_Fds;