xref: /petsc/src/sys/classes/viewer/impls/socket/send.c (revision 74df5e01f481fb3fe90b32c3b4345ef0122eb3ce)
1 #include <petscsys.h> /*I  "petscviewer.h"  I*/
2 
3 #if defined(PETSC_NEEDS_UTYPE_TYPEDEFS)
4 /* Some systems have inconsistent include files that use but do not
5    ensure that the following definitions are made */
6 typedef unsigned char  u_char;
7 typedef unsigned short u_short;
8 typedef unsigned short ushort;
9 typedef unsigned int   u_int;
10 typedef unsigned long  u_long;
11 #endif
12 
13 #include <errno.h>
14 #include <ctype.h>
15 #if defined(PETSC_HAVE_MACHINE_ENDIAN_H)
16   #include <machine/endian.h>
17 #endif
18 #if defined(PETSC_HAVE_UNISTD_H)
19   #include <unistd.h>
20 #endif
21 #if defined(PETSC_HAVE_SYS_SOCKET_H)
22   #include <sys/socket.h>
23 #endif
24 #if defined(PETSC_HAVE_SYS_WAIT_H)
25   #include <sys/wait.h>
26 #endif
27 #if defined(PETSC_HAVE_NETINET_IN_H)
28   #include <netinet/in.h>
29 #endif
30 #if defined(PETSC_HAVE_NETDB_H)
31   #include <netdb.h>
32 #endif
33 #if defined(PETSC_HAVE_FCNTL_H)
34   #include <fcntl.h>
35 #endif
36 #if defined(PETSC_HAVE_IO_H)
37   #include <io.h>
38 #endif
39 #if defined(PETSC_HAVE_WINSOCK2_H)
40   #include <Winsock2.h>
41 #endif
42 #include <sys/stat.h>
43 #include <../src/sys/classes/viewer/impls/socket/socket.h>
44 
45 #if defined(PETSC_NEED_CLOSE_PROTO)
46 PETSC_EXTERN int close(int);
47 #endif
48 #if defined(PETSC_NEED_SOCKET_PROTO)
49 PETSC_EXTERN int socket(int, int, int);
50 #endif
51 #if defined(PETSC_NEED_SLEEP_PROTO)
52 PETSC_EXTERN int sleep(unsigned);
53 #endif
54 #if defined(PETSC_NEED_CONNECT_PROTO)
55 PETSC_EXTERN int connect(int, struct sockaddr *, int);
56 #endif
57 
58 static PetscErrorCode PetscViewerDestroy_Socket(PetscViewer viewer)
59 {
60   PetscViewer_Socket *vmatlab = (PetscViewer_Socket *)viewer->data;
61 
62   PetscFunctionBegin;
63   if (vmatlab->port) {
64     int ierr;
65 
66 #if defined(PETSC_HAVE_CLOSESOCKET)
67     ierr = closesocket(vmatlab->port);
68 #else
69     ierr = close(vmatlab->port);
70 #endif
71     PetscCheck(!ierr, PETSC_COMM_SELF, PETSC_ERR_SYS, "System error closing socket");
72   }
73   PetscCall(PetscFree(vmatlab));
74   PetscCall(PetscObjectComposeFunction((PetscObject)viewer, "PetscViewerBinarySetSkipHeader_C", NULL));
75   PetscCall(PetscObjectComposeFunction((PetscObject)viewer, "PetscViewerBinaryGetSkipHeader_C", NULL));
76   PetscCall(PetscObjectComposeFunction((PetscObject)viewer, "PetscViewerBinaryGetFlowControl_C", NULL));
77   PetscFunctionReturn(PETSC_SUCCESS);
78 }
79 
80 /*@
81   PetscOpenSocket - handles connected to an open port where someone is waiting.
82 
83   Input Parameters:
84 + hostname - for example www.mcs.anl.gov
85 - portnum  - for example 80
86 
87   Output Parameter:
88 . t - the socket number
89 
90   Notes:
91   Use close() to close the socket connection
92 
93   Use read() or `PetscHTTPRequest()` to read from the socket
94 
95   Level: advanced
96 
97 .seealso: `PetscSocketListen()`, `PetscSocketEstablish()`, `PetscHTTPRequest()`, `PetscHTTPSConnect()`
98 @*/
99 PetscErrorCode PetscOpenSocket(const char hostname[], int portnum, int *t)
100 {
101   struct sockaddr_in sa;
102   struct hostent    *hp;
103   int                s      = 0;
104   PetscBool          flg    = PETSC_TRUE;
105   static int         refcnt = 0;
106 
107   PetscFunctionBegin;
108   if (!(hp = gethostbyname(hostname))) {
109     perror("SEND: error gethostbyname: ");
110     SETERRQ(PETSC_COMM_SELF, PETSC_ERR_SYS, "system error open connection to %s", hostname);
111   }
112   PetscCall(PetscMemzero(&sa, sizeof(sa)));
113   PetscCall(PetscMemcpy(&sa.sin_addr, hp->h_addr_list[0], hp->h_length));
114 
115   sa.sin_family = (unsigned char)hp->h_addrtype;
116   sa.sin_port   = htons((u_short)portnum);
117   while (flg) {
118     if ((s = socket(hp->h_addrtype, SOCK_STREAM, 0)) < 0) {
119       perror("SEND: error socket");
120       SETERRQ(PETSC_COMM_SELF, PETSC_ERR_SYS, "system error");
121     }
122     if (connect(s, (struct sockaddr *)&sa, sizeof(sa)) < 0) {
123 #if defined(PETSC_HAVE_WSAGETLASTERROR)
124       ierr = WSAGetLastError();
125       if (ierr == WSAEADDRINUSE) (*PetscErrorPrintf)("SEND: address is in use\n");
126       else if (ierr == WSAEALREADY) (*PetscErrorPrintf)("SEND: socket is non-blocking \n");
127       else if (ierr == WSAEISCONN) {
128         (*PetscErrorPrintf)("SEND: socket already connected\n");
129         Sleep((unsigned)1);
130       } else if (ierr == WSAECONNREFUSED) {
131         /* (*PetscErrorPrintf)("SEND: forcefully rejected\n"); */
132         Sleep((unsigned)1);
133       } else {
134         perror(NULL);
135         SETERRQ(PETSC_COMM_SELF, PETSC_ERR_SYS, "system error");
136       }
137 #else
138       if (errno == EADDRINUSE) {
139         PetscErrorCode ierr = (*PetscErrorPrintf)("SEND: address is in use\n");
140         (void)ierr;
141       } else if (errno == EALREADY) {
142         PetscErrorCode ierr = (*PetscErrorPrintf)("SEND: socket is non-blocking \n");
143         (void)ierr;
144       } else if (errno == EISCONN) {
145         PetscErrorCode ierr = (*PetscErrorPrintf)("SEND: socket already connected\n");
146         (void)ierr;
147         sleep((unsigned)1);
148       } else if (errno == ECONNREFUSED) {
149         refcnt++;
150         PetscCheck(refcnt <= 5, PETSC_COMM_SELF, PETSC_ERR_SYS, "Connection refused by remote host %s port %d", hostname, portnum);
151         PetscCall(PetscInfo(NULL, "Connection refused in attaching socket, trying again\n"));
152         sleep((unsigned)1);
153       } else {
154         perror(NULL);
155         SETERRQ(PETSC_COMM_SELF, PETSC_ERR_SYS, "system error");
156       }
157 #endif
158       flg = PETSC_TRUE;
159 #if defined(PETSC_HAVE_CLOSESOCKET)
160       closesocket(s);
161 #else
162       close(s);
163 #endif
164     } else flg = PETSC_FALSE;
165   }
166   *t = s;
167   PetscFunctionReturn(PETSC_SUCCESS);
168 }
169 
170 /*
171    PetscSocketEstablish - starts a listener on a socket
172 
173    Input Parameter:
174 .    portnumber - the port to wait at
175 
176    Output Parameter:
177 .     ss - the socket to be used with `PetscSocketListen()`
178 
179     Level: advanced
180 
181 .seealso: `PetscSocketListen()`, `PetscOpenSocket()`
182 */
183 static PetscErrorCode PetscSocketEstablish(int portnum, int *ss)
184 {
185   char               myname[PETSC_MAX_OPTION_NAME];
186   int                s;
187   struct sockaddr_in sa;
188   struct hostent    *hp;
189 
190   PetscFunctionBegin;
191   PetscCall(PetscGetHostName(myname, sizeof(myname)));
192 
193   PetscCall(PetscMemzero(&sa, sizeof(struct sockaddr_in)));
194 
195   hp = gethostbyname(myname);
196   PetscCheck(hp, PETSC_COMM_SELF, PETSC_ERR_SYS, "Unable to get hostent information from system");
197 
198   sa.sin_family = (unsigned char)hp->h_addrtype;
199   sa.sin_port   = htons((u_short)portnum);
200 
201   PetscCheck((s = socket(AF_INET, SOCK_STREAM, 0)) >= 0, PETSC_COMM_SELF, PETSC_ERR_SYS, "Error running socket() command");
202 #if defined(PETSC_HAVE_SO_REUSEADDR)
203   {
204     int optval = 1; /* Turn on the option */
205     int ret    = setsockopt(s, SOL_SOCKET, SO_REUSEADDR, (char *)&optval, sizeof(optval));
206     PetscCheck(!ret, PETSC_COMM_SELF, PETSC_ERR_LIB, "setsockopt() failed with error code %d", ret);
207   }
208 #endif
209 
210   while (bind(s, (struct sockaddr *)&sa, sizeof(sa)) < 0) {
211 #if defined(PETSC_HAVE_WSAGETLASTERROR)
212     ierr = WSAGetLastError();
213     if (ierr != WSAEADDRINUSE) {
214 #else
215     if (errno != EADDRINUSE) {
216 #endif
217       close(s);
218       SETERRQ(PETSC_COMM_SELF, PETSC_ERR_SYS, "Error from bind()");
219     }
220   }
221   listen(s, 0);
222   *ss = s;
223   PetscFunctionReturn(PETSC_SUCCESS);
224 }
225 
226 /*
227    PetscSocketListen - Listens at a socket created with `PetscSocketEstablish()`
228 
229    Input Parameter:
230 .    listenport - obtained with `PetscSocketEstablish()`
231 
232    Output Parameter:
233 .     t - pass this to read() to read what is passed to this connection
234 
235     Level: advanced
236 
237 .seealso: `PetscSocketEstablish()`
238 */
239 static PetscErrorCode PetscSocketListen(int listenport, int *t)
240 {
241   struct sockaddr_in isa;
242 #if defined(PETSC_HAVE_ACCEPT_SIZE_T)
243   size_t i;
244 #else
245   int i;
246 #endif
247 
248   PetscFunctionBegin;
249   /* wait for someone to try to connect */
250   i = sizeof(struct sockaddr_in);
251   PetscCheck((*t = accept(listenport, (struct sockaddr *)&isa, (socklen_t *)&i)) >= 0, PETSC_COMM_SELF, PETSC_ERR_SYS, "error from accept()");
252   PetscFunctionReturn(PETSC_SUCCESS);
253 }
254 
255 // "Unknown section 'Environmental Variables'"
256 // PetscClangLinter pragma disable: -fdoc-section-header-unknown
257 /*@
258   PetscViewerSocketOpen - Opens a connection to a MATLAB or other socket based server.
259 
260   Collective
261 
262   Input Parameters:
263 + comm    - the MPI communicator
264 . machine - the machine the server is running on, use `NULL` for the local machine, use "server" to passively wait for
265              a connection from elsewhere
266 - port    - the port to connect to, use `PETSC_DEFAULT` for the default
267 
268   Output Parameter:
269 . lab - a context to use when communicating with the server
270 
271   Options Database Keys:
272    For use with  `PETSC_VIEWER_SOCKET_WORLD`, `PETSC_VIEWER_SOCKET_SELF`,
273    `PETSC_VIEWER_SOCKET_()` or if
274     `NULL` is passed for machine or PETSC_DEFAULT is passed for port
275 + -viewer_socket_machine <machine> - the machine where the socket is available
276 - -viewer_socket_port <port>       - the socket to connect to
277 
278   Environmental variables:
279 +   `PETSC_VIEWER_SOCKET_MACHINE` - machine name
280 -   `PETSC_VIEWER_SOCKET_PORT` - portnumber
281 
282   Level: intermediate
283 
284   Notes:
285   Most users should employ the following commands to access the
286   MATLAB `PetscViewer`
287 .vb
288 
289     PetscViewerSocketOpen(MPI_Comm comm, char *machine,int port,PetscViewer &viewer)
290     MatView(Mat matrix,PetscViewer viewer)
291 .ve
292   or
293 .vb
294     PetscViewerSocketOpen(MPI_Comm comm,char *machine,int port,PetscViewer &viewer)
295     VecView(Vec vector,PetscViewer viewer)
296 .ve
297 
298   Currently the only socket client available is MATLAB, PETSc must be configured with --with-matlab for this client. See
299   src/dm/tests/ex12.c and ex12.m for an example of usage.
300 
301   The socket viewer is in some sense a subclass of the binary viewer, to read and write to the socket
302   use `PetscViewerBinaryRead()`, `PetscViewerBinaryWrite()`, `PetscViewerBinarWriteStringArray()`, `PetscViewerBinaryGetDescriptor()`.
303 
304   Use this for communicating with an interactive MATLAB session, see `PETSC_VIEWER_MATLAB_()` for writing output to a
305   .mat file. Use `PetscMatlabEngineCreate()` or `PETSC_MATLAB_ENGINE_()`, `PETSC_MATLAB_ENGINE_SELF`, or `PETSC_MATLAB_ENGINE_WORLD`
306   for communicating with a MATLAB Engine
307 
308 .seealso: [](sec_viewers), `PETSCVIEWERBINARY`, `PETSCVIEWERSOCKET`, `MatView()`, `VecView()`, `PetscViewerDestroy()`, `PetscViewerCreate()`, `PetscViewerSetType()`,
309           `PetscViewerSocketSetConnection()`, `PETSC_VIEWER_SOCKET_`, `PETSC_VIEWER_SOCKET_WORLD`,
310           `PETSC_VIEWER_SOCKET_SELF`, `PetscViewerBinaryWrite()`, `PetscViewerBinaryRead()`, `PetscViewerBinaryWriteStringArray()`,
311           `PetscBinaryViewerGetDescriptor()`, `PetscMatlabEngineCreate()`
312 @*/
313 PetscErrorCode PetscViewerSocketOpen(MPI_Comm comm, const char machine[], int port, PetscViewer *lab)
314 {
315   PetscFunctionBegin;
316   PetscCall(PetscViewerCreate(comm, lab));
317   PetscCall(PetscViewerSetType(*lab, PETSCVIEWERSOCKET));
318   PetscCall(PetscViewerSocketSetConnection(*lab, machine, port));
319   PetscFunctionReturn(PETSC_SUCCESS);
320 }
321 
322 static PetscErrorCode PetscViewerSetFromOptions_Socket(PetscViewer v, PetscOptionItems PetscOptionsObject)
323 {
324   PetscInt  def = -1;
325   char      sdef[256];
326   PetscBool tflg;
327 
328   PetscFunctionBegin;
329   /*
330        These options are not processed here, they are processed in PetscViewerSocketSetConnection(), they
331     are listed here for the GUI to display
332   */
333   PetscOptionsHeadBegin(PetscOptionsObject, "Socket PetscViewer Options");
334   PetscCall(PetscOptionsGetenv(PetscObjectComm((PetscObject)v), "PETSC_VIEWER_SOCKET_PORT", sdef, 16, &tflg));
335   if (tflg) PetscCall(PetscOptionsStringToInt(sdef, &def));
336   else def = PETSCSOCKETDEFAULTPORT;
337   PetscCall(PetscOptionsInt("-viewer_socket_port", "Port number to use for socket", "PetscViewerSocketSetConnection", def, NULL, NULL));
338 
339   PetscCall(PetscOptionsString("-viewer_socket_machine", "Machine to use for socket", "PetscViewerSocketSetConnection", sdef, NULL, sizeof(sdef), NULL));
340   PetscCall(PetscOptionsGetenv(PetscObjectComm((PetscObject)v), "PETSC_VIEWER_SOCKET_MACHINE", sdef, sizeof(sdef), &tflg));
341   if (!tflg) PetscCall(PetscGetHostName(sdef, sizeof(sdef)));
342   PetscOptionsHeadEnd();
343   PetscFunctionReturn(PETSC_SUCCESS);
344 }
345 
346 static PetscErrorCode PetscViewerBinaryGetSkipHeader_Socket(PetscViewer viewer, PetscBool *skip)
347 {
348   PetscViewer_Socket *vsocket = (PetscViewer_Socket *)viewer->data;
349 
350   PetscFunctionBegin;
351   *skip = vsocket->skipheader;
352   PetscFunctionReturn(PETSC_SUCCESS);
353 }
354 
355 static PetscErrorCode PetscViewerBinarySetSkipHeader_Socket(PetscViewer viewer, PetscBool skip)
356 {
357   PetscViewer_Socket *vsocket = (PetscViewer_Socket *)viewer->data;
358 
359   PetscFunctionBegin;
360   vsocket->skipheader = skip;
361   PetscFunctionReturn(PETSC_SUCCESS);
362 }
363 
364 PETSC_INTERN PetscErrorCode PetscViewerBinaryGetFlowControl_Binary(PetscViewer, PetscInt *);
365 
366 /*MC
367    PETSCVIEWERSOCKET - A viewer that writes to a Unix socket
368 
369   Level: beginner
370 
371 .seealso: [](sec_viewers), `PETSC_VIEWERBINARY`, `PetscViewerSocketOpen()`, `PetscViewerDrawOpen()`, `PETSC_VIEWER_DRAW_()`, `PETSC_VIEWER_DRAW_SELF`, `PETSC_VIEWER_DRAW_WORLD`,
372           `PetscViewerCreate()`, `PetscViewerASCIIOpen()`, `PetscViewerBinaryOpen()`, `PETSCVIEWERBINARY`, `PETSCVIEWERDRAW`,
373           `PetscViewerMatlabOpen()`, `VecView()`, `DMView()`, `PetscViewerMatlabPutArray()`, `PETSCVIEWERASCII`, `PETSCVIEWERMATLAB`,
374           `PetscViewerFileSetName()`, `PetscViewerFileSetMode()`, `PetscViewerFormat`, `PetscViewerType`, `PetscViewerSetType()`
375 M*/
376 
377 PETSC_EXTERN PetscErrorCode PetscViewerCreate_Socket(PetscViewer v)
378 {
379   PetscViewer_Socket *vmatlab;
380 
381   PetscFunctionBegin;
382   PetscCall(PetscNew(&vmatlab));
383   vmatlab->port          = 0;
384   vmatlab->flowcontrol   = 256; /* same default as in PetscViewerCreate_Binary() */
385   v->data                = (void *)vmatlab;
386   v->ops->destroy        = PetscViewerDestroy_Socket;
387   v->ops->flush          = NULL;
388   v->ops->setfromoptions = PetscViewerSetFromOptions_Socket;
389 
390   /* lie and say this is a binary viewer; then all the XXXView_Binary() methods will work correctly on it */
391   PetscCall(PetscObjectChangeTypeName((PetscObject)v, PETSCVIEWERBINARY));
392   PetscCall(PetscObjectComposeFunction((PetscObject)v, "PetscViewerBinarySetSkipHeader_C", PetscViewerBinarySetSkipHeader_Socket));
393   PetscCall(PetscObjectComposeFunction((PetscObject)v, "PetscViewerBinaryGetSkipHeader_C", PetscViewerBinaryGetSkipHeader_Socket));
394   PetscCall(PetscObjectComposeFunction((PetscObject)v, "PetscViewerBinaryGetFlowControl_C", PetscViewerBinaryGetFlowControl_Binary));
395   PetscFunctionReturn(PETSC_SUCCESS);
396 }
397 
398 /*@
399   PetscViewerSocketSetConnection - Sets the machine and port that a PETSc socket
400   viewer is to use
401 
402   Logically Collective
403 
404   Input Parameters:
405 + v       - viewer to connect
406 . machine - host to connect to, use `NULL` for the local machine,use "server" to passively wait for
407              a connection from elsewhere
408 - port    - the port on the machine one is connecting to, use `PETSC_DEFAULT` for default
409 
410   Level: advanced
411 
412 .seealso: [](sec_viewers), `PETSCVIEWERMATLAB`, `PETSCVIEWERSOCKET`, `PetscViewerSocketOpen()`
413 @*/
414 PetscErrorCode PetscViewerSocketSetConnection(PetscViewer v, const char machine[], int port)
415 {
416   PetscMPIInt         rank;
417   char                mach[256];
418   PetscBool           tflg;
419   PetscViewer_Socket *vmatlab;
420 
421   PetscFunctionBegin;
422   PetscValidHeaderSpecific(v, PETSC_VIEWER_CLASSID, 1);
423   if (machine) PetscAssertPointer(machine, 2);
424   vmatlab = (PetscViewer_Socket *)v->data;
425   /* PetscValidLogicalCollectiveInt(v,port,3); not a PetscInt */
426   if (port <= 0) {
427     char portn[16];
428     PetscCall(PetscOptionsGetenv(PetscObjectComm((PetscObject)v), "PETSC_VIEWER_SOCKET_PORT", portn, 16, &tflg));
429     if (tflg) {
430       PetscInt pport;
431       PetscCall(PetscOptionsStringToInt(portn, &pport));
432       PetscCall(PetscMPIIntCast(pport, &port));
433     } else port = PETSCSOCKETDEFAULTPORT;
434   }
435   if (!machine) {
436     PetscCall(PetscOptionsGetenv(PetscObjectComm((PetscObject)v), "PETSC_VIEWER_SOCKET_MACHINE", mach, sizeof(mach), &tflg));
437     if (!tflg) PetscCall(PetscGetHostName(mach, sizeof(mach)));
438   } else {
439     PetscCall(PetscStrncpy(mach, machine, sizeof(mach)));
440   }
441 
442   PetscCallMPI(MPI_Comm_rank(PetscObjectComm((PetscObject)v), &rank));
443   if (rank == 0) {
444     PetscCall(PetscStrcmp(mach, "server", &tflg));
445     if (tflg) {
446       int listenport = 0;
447 
448       PetscCall(PetscInfo(v, "Waiting for connection from socket process on port %d\n", port));
449       PetscCall(PetscSocketEstablish(port, &listenport));
450       PetscCall(PetscSocketListen(listenport, &vmatlab->port));
451       close(listenport);
452     } else {
453       PetscCall(PetscInfo(v, "Connecting to socket process on port %d machine %s\n", port, mach));
454       PetscCall(PetscOpenSocket(mach, port, &vmatlab->port));
455     }
456   }
457   PetscFunctionReturn(PETSC_SUCCESS);
458 }
459 
460 /*
461     The variable Petsc_Viewer_Socket_keyval is used to indicate an MPI attribute that
462   is attached to a communicator, in this case the attribute is a PetscViewer.
463 */
464 PetscMPIInt Petsc_Viewer_Socket_keyval = MPI_KEYVAL_INVALID;
465 
466 /*@C
467    PETSC_VIEWER_SOCKET_ - Creates a socket viewer shared by all processors in a communicator.
468 
469    Collective
470 
471    Input Parameter:
472 .  comm - the MPI communicator to share the  `PETSCVIEWERSOCKET` `PetscViewer`
473 
474    Level: intermediate
475 
476    Options Database Keys:
477    For use with the default `PETSC_VIEWER_SOCKET_WORLD` or if
478    `NULL` is passed for machine or `PETSC_DEFAULT` is passed for port
479 +  -viewer_socket_machine <machine> - machine to connect to
480 -  -viewer_socket_port <port> - port to connect to
481 
482    Environmental variables:
483 +  `PETSC_VIEWER_SOCKET_PORT` - portnumber
484 -  `PETSC_VIEWER_SOCKET_MACHINE` - machine name
485 
486    Notes:
487    This object is destroyed in `PetscFinalize()`, `PetscViewerDestroy()` should never be called on it
488 
489    Unlike almost all other PETSc routines, `PETSC_VIEWER_SOCKET_()` does not return
490    an error code, it returns `NULL` if it fails. The  `PETSCVIEWERSOCKET`  `PetscViewer` is usually used in the form `XXXView(XXX object, PETSC_VIEWER_SOCKET_(comm))`
491 
492    Currently the only socket client available is MATLAB. See
493    src/dm/tests/ex12.c and ex12.m for an example of usage.
494 
495    Connects to a waiting socket and stays connected until `PetscViewerDestroy()` is called.
496 
497    Use this for communicating with an interactive MATLAB session, see `PETSC_VIEWER_MATLAB_()` for writing output to a
498    .mat file. Use `PetscMatlabEngineCreate()` or `PETSC_MATLAB_ENGINE_()`, `PETSC_MATLAB_ENGINE_SELF`, or `PETSC_MATLAB_ENGINE_WORLD`
499    for communicating with a MATLAB Engine
500 
501 .seealso: [](sec_viewers), `PETSCVIEWERMATLAB`, `PETSCVIEWERSOCKET`, `PETSC_VIEWER_SOCKET_WORLD`, `PETSC_VIEWER_SOCKET_SELF`, `PetscViewerSocketOpen()`, `PetscViewerCreate()`,
502           `PetscViewerSocketSetConnection()`, `PetscViewerDestroy()`, `PETSC_VIEWER_SOCKET_()`, `PetscViewerBinaryWrite()`, `PetscViewerBinaryRead()`,
503           `PetscViewerBinaryWriteStringArray()`, `PetscViewerBinaryGetDescriptor()`, `PETSC_VIEWER_MATLAB_()`
504 @*/
505 PetscViewer PETSC_VIEWER_SOCKET_(MPI_Comm comm)
506 {
507   PetscMPIInt iflg;
508   PetscViewer viewer;
509   MPI_Comm    ncomm;
510 
511   PetscFunctionBegin;
512   PetscCallNull(PetscCommDuplicate(comm, &ncomm, NULL));
513   if (Petsc_Viewer_Socket_keyval == MPI_KEYVAL_INVALID) PetscCallMPINull(MPI_Comm_create_keyval(MPI_COMM_NULL_COPY_FN, MPI_COMM_NULL_DELETE_FN, &Petsc_Viewer_Socket_keyval, NULL));
514   PetscCallMPINull(MPI_Comm_get_attr(ncomm, Petsc_Viewer_Socket_keyval, (void **)&viewer, &iflg));
515   if (!iflg) { /* PetscViewer not yet created */
516     PetscCallNull(PetscViewerSocketOpen(ncomm, NULL, 0, &viewer));
517     PetscCallNull(PetscObjectRegisterDestroy((PetscObject)viewer));
518     PetscCallMPINull(MPI_Comm_set_attr(ncomm, Petsc_Viewer_Socket_keyval, (void *)viewer));
519   }
520   PetscCallNull(PetscCommDestroy(&ncomm));
521   PetscFunctionReturn(viewer);
522 }
523