gdb/gdbserver/event-loop.c

   1 /* Event loop machinery for the remote server for GDB.
   2    Copyright (C) 1999, 2000, 2001, 2002, 2005, 2006, 2007, 2008
   3    Free Software Foundation, Inc.
   4
   5    This file is part of GDB.
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 3 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program.  If not, see <http://www.gnu.org/licenses/>. */
  19
  20 /* Based on src/gdb/event-loop.c.  */
  21
  22 #include "server.h"
  23
  24 #include <sys/types.h>
  25 #include <string.h>
  26 #include <sys/time.h>
  27
  28 #ifdef USE_WIN32API
  29 #include <windows.h>
  30 #include <io.h>
  31 #endif
  32
  33 #ifdef HAVE_ERRNO_H
  34 #include <errno.h>
  35 #endif
  36
  37 #ifdef HAVE_UNISTD_H
  38 #include <unistd.h>
  39 #endif
  40
  41 typedef struct gdb_event gdb_event;
  42 typedef void (event_handler_func) (int);
  43
  44 /* Tell create_file_handler what events we are interested in.  */
  45
  46 #define GDB_READABLE    (1<<1)
  47 #define GDB_WRITABLE    (1<<2)
  48 #define GDB_EXCEPTION   (1<<3)
  49
  50 /* Events are queued by calling async_queue_event and serviced later
  51    on by do_one_event.  An event can be, for instance, a file
  52    descriptor becoming ready to be read.  Servicing an event simply
  53    means that the procedure PROC will be called.  We have 2 queues,
  54    one for file handlers that we listen to in the event loop, and one
  55    for the file handlers+events that are ready.  The procedure PROC
  56    associated with each event is always the same (handle_file_event).
  57    Its duty is to invoke the handler associated with the file
  58    descriptor whose state change generated the event, plus doing other
  59    cleanups and such.  */
  60
  61 struct gdb_event
  62   {
  63     /* Procedure to call to service this event.  */
  64     event_handler_func *proc;
  65
  66     /* File descriptor that is ready.  */
  67     int fd;
  68
  69     /* Next in list of events or NULL.  */
  70     struct gdb_event *next_event;
  71   };
  72
  73 /* Information about each file descriptor we register with the event
  74    loop.  */
  75
  76 typedef struct file_handler
  77   {
  78     /* File descriptor.  */
  79     int fd;
  80
  81     /* Events we want to monitor.  */
  82     int mask;
  83
  84     /* Events that have been seen since the last time.  */
  85     int ready_mask;
  86
  87     /* Procedure to call when fd is ready.  */
  88     handler_func *proc;
  89
  90     /* Argument to pass to proc.  */
  91     gdb_client_data client_data;
  92
  93     /* Was an error detected on this fd?  */
  94     int error;
  95
  96     /* Next registered file descriptor.  */
  97     struct file_handler *next_file;
  98   }
  99 file_handler;
 100
 101 /* Event queue:
 102
 103    Events can be inserted at the front of the queue or at the end of
 104    the queue.  Events will be extracted from the queue for processing
 105    starting from the head.  Therefore, events inserted at the head of
 106    the queue will be processed in a last in first out fashion, while
 107    those inserted at the tail of the queue will be processed in a
 108    first in first out manner.  All the fields are NULL if the queue is
 109    empty.  */
 110
 111 static struct
 112   {
 113     /* The first pending event.  */
 114     gdb_event *first_event;
 115
 116     /* The last pending event.  */
 117     gdb_event *last_event;
 118   }
 119 event_queue;
 120
 121 /* Gdb_notifier is just a list of file descriptors gdb is interested
 122    in.  These are the input file descriptor, and the target file
 123    descriptor.  Each of the elements in the gdb_notifier list is
 124    basically a description of what kind of events gdb is interested
 125    in, for each fd.  */
 126
 127 static struct
 128   {
 129     /* Ptr to head of file handler list.  */
 130     file_handler *first_file_handler;
 131
 132     /* Masks to be used in the next call to select.  Bits are set in
 133        response to calls to create_file_handler.  */
 134     fd_set check_masks[3];
 135
 136     /* What file descriptors were found ready by select.  */
 137     fd_set ready_masks[3];
 138
 139     /* Number of valid bits (highest fd value + 1). (for select) */
 140     int num_fds;
 141   }
 142 gdb_notifier;
 143
 144 /* Insert an event object into the gdb event queue.
 145
 146    EVENT_PTR points to the event to be inserted into the queue.  The
 147    caller must allocate memory for the event.  It is freed after the
 148    event has ben handled.  Events in the queue will be processed head
 149    to tail, therefore, events will be processed first in first
 150    out.  */
 151
 152 static void
 153 async_queue_event (gdb_event *event_ptr)
 154 {
 155   /* The event will become the new last_event.  */
 156
 157   event_ptr->next_event = NULL;
 158   if (event_queue.first_event == NULL)
 159     event_queue.first_event = event_ptr;
 160   else
 161     event_queue.last_event->next_event = event_ptr;
 162   event_queue.last_event = event_ptr;
 163 }
 164
 165 /* Process one event.  If an event was processed, 1 is returned
 166    otherwise 0 is returned.  Scan the queue from head to tail,
 167    processing therefore the high priority events first, by invoking
 168    the associated event handler procedure.  */
 169
 170 static int
 171 process_event (void)
 172 {
 173   gdb_event *event_ptr, *prev_ptr;
 174   event_handler_func *proc;
 175   int fd;
 176
 177   /* Look in the event queue to find an event that is ready
 178      to be processed.  */
 179
 180   for (event_ptr = event_queue.first_event;
 181        event_ptr != NULL;
 182        event_ptr = event_ptr->next_event)
 183     {
 184       /* Call the handler for the event.  */
 185
 186       proc = event_ptr->proc;
 187       fd = event_ptr->fd;
 188
 189       /* Let's get rid of the event from the event queue.  We need to
 190          do this now because while processing the event, since the
 191          proc function could end up jumping out to the caller of this
 192          function.  In that case, we would have on the event queue an
 193          event which has been processed, but not deleted.  */
 194
 195       if (event_queue.first_event == event_ptr)
 196         {
 197           event_queue.first_event = event_ptr->next_event;
 198           if (event_ptr->next_event == NULL)
 199             event_queue.last_event = NULL;
 200         }
 201       else
 202         {
 203           prev_ptr = event_queue.first_event;
 204           while (prev_ptr->next_event != event_ptr)
 205             prev_ptr = prev_ptr->next_event;
 206
 207           prev_ptr->next_event = event_ptr->next_event;
 208           if (event_ptr->next_event == NULL)
 209             event_queue.last_event = prev_ptr;
 210         }
 211       free (event_ptr);
 212
 213       /* Now call the procedure associated with the event.  */
 214       (*proc) (fd);
 215       return 1;
 216     }
 217
 218   /* This is the case if there are no event on the event queue.  */
 219   return 0;
 220 }
 221
 222 /* Add a file handler/descriptor to the list of descriptors we are
 223    interested in.  FD is the file descriptor for the file/stream to be
 224    listened to.  MASK is a combination of READABLE, WRITABLE,
 225    EXCEPTION.  PROC is the procedure that will be called when an event
 226    occurs for FD.  CLIENT_DATA is the argument to pass to PROC.  */
 227
 228 static void
 229 create_file_handler (int fd, int mask, handler_func *proc,
 230                      gdb_client_data client_data)
 231 {
 232   file_handler *file_ptr;
 233
 234   /* Do we already have a file handler for this file? (We may be
 235      changing its associated procedure).  */
 236   for (file_ptr = gdb_notifier.first_file_handler;
 237        file_ptr != NULL;
 238        file_ptr = file_ptr->next_file)
 239     if (file_ptr->fd == fd)
 240       break;
 241
 242   /* It is a new file descriptor.  Add it to the list.  Otherwise,
 243      just change the data associated with it.  */
 244   if (file_ptr == NULL)
 245     {
 246       file_ptr = xmalloc (sizeof (*file_ptr));
 247       file_ptr->fd = fd;
 248       file_ptr->ready_mask = 0;
 249       file_ptr->next_file = gdb_notifier.first_file_handler;
 250       gdb_notifier.first_file_handler = file_ptr;
 251
 252       if (mask & GDB_READABLE)
 253         FD_SET (fd, &gdb_notifier.check_masks[0]);
 254       else
 255         FD_CLR (fd, &gdb_notifier.check_masks[0]);
 256
 257       if (mask & GDB_WRITABLE)
 258         FD_SET (fd, &gdb_notifier.check_masks[1]);
 259       else
 260         FD_CLR (fd, &gdb_notifier.check_masks[1]);
 261
 262       if (mask & GDB_EXCEPTION)
 263         FD_SET (fd, &gdb_notifier.check_masks[2]);
 264       else
 265         FD_CLR (fd, &gdb_notifier.check_masks[2]);
 266
 267       if (gdb_notifier.num_fds <= fd)
 268         gdb_notifier.num_fds = fd + 1;
 269     }
 270
 271   file_ptr->proc = proc;
 272   file_ptr->client_data = client_data;
 273   file_ptr->mask = mask;
 274 }
 275
 276 /* Wrapper function for create_file_handler.  */
 277
 278 void
 279 add_file_handler (int fd, handler_func *proc, gdb_client_data client_data)
 280 {
 281   create_file_handler (fd, GDB_READABLE | GDB_EXCEPTION, proc, client_data);
 282 }
 283
 284 /* Remove the file descriptor FD from the list of monitored fd's:
 285    i.e. we don't care anymore about events on the FD.  */
 286
 287 void
 288 delete_file_handler (int fd)
 289 {
 290   file_handler *file_ptr, *prev_ptr = NULL;
 291   int i;
 292
 293   /* Find the entry for the given file. */
 294
 295   for (file_ptr = gdb_notifier.first_file_handler;
 296        file_ptr != NULL;
 297        file_ptr = file_ptr->next_file)
 298     if (file_ptr->fd == fd)
 299       break;
 300
 301   if (file_ptr == NULL)
 302     return;
 303
 304   if (file_ptr->mask & GDB_READABLE)
 305     FD_CLR (fd, &gdb_notifier.check_masks[0]);
 306   if (file_ptr->mask & GDB_WRITABLE)
 307     FD_CLR (fd, &gdb_notifier.check_masks[1]);
 308   if (file_ptr->mask & GDB_EXCEPTION)
 309     FD_CLR (fd, &gdb_notifier.check_masks[2]);
 310
 311   /* Find current max fd.  */
 312
 313   if ((fd + 1) == gdb_notifier.num_fds)
 314     {
 315       gdb_notifier.num_fds--;
 316       for (i = gdb_notifier.num_fds; i; i--)
 317         {
 318           if (FD_ISSET (i - 1, &gdb_notifier.check_masks[0])
 319               || FD_ISSET (i - 1, &gdb_notifier.check_masks[1])
 320               || FD_ISSET (i - 1, &gdb_notifier.check_masks[2]))
 321             break;
 322         }
 323       gdb_notifier.num_fds = i;
 324     }
 325
 326   /* Deactivate the file descriptor, by clearing its mask, so that it
 327      will not fire again.  */
 328
 329   file_ptr->mask = 0;
 330
 331   /* Get rid of the file handler in the file handler list.  */
 332   if (file_ptr == gdb_notifier.first_file_handler)
 333     gdb_notifier.first_file_handler = file_ptr->next_file;
 334   else
 335     {
 336       for (prev_ptr = gdb_notifier.first_file_handler;
 337            prev_ptr->next_file != file_ptr;
 338            prev_ptr = prev_ptr->next_file)
 339         ;
 340       prev_ptr->next_file = file_ptr->next_file;
 341     }
 342   free (file_ptr);
 343 }
 344
 345 /* Handle the given event by calling the procedure associated to the
 346    corresponding file handler.  Called by process_event indirectly,
 347    through event_ptr->proc.  EVENT_FILE_DESC is file descriptor of the
 348    event in the front of the event queue.  */
 349
 350 static void
 351 handle_file_event (int event_file_desc)
 352 {
 353   file_handler *file_ptr;
 354   int mask;
 355
 356   /* Search the file handler list to find one that matches the fd in
 357      the event.  */
 358   for (file_ptr = gdb_notifier.first_file_handler; file_ptr != NULL;
 359        file_ptr = file_ptr->next_file)
 360     {
 361       if (file_ptr->fd == event_file_desc)
 362         {
 363           /* See if the desired events (mask) match the received
 364              events (ready_mask).  */
 365
 366           if (file_ptr->ready_mask & GDB_EXCEPTION)
 367             {
 368               fprintf (stderr, "Exception condition detected on fd %d\n",
 369                        file_ptr->fd);
 370               file_ptr->error = 1;
 371             }
 372           else
 373             file_ptr->error = 0;
 374           mask = file_ptr->ready_mask & file_ptr->mask;
 375
 376           /* Clear the received events for next time around.  */
 377           file_ptr->ready_mask = 0;
 378
 379           /* If there was a match, then call the handler.  */
 380           if (mask != 0)
 381             (*file_ptr->proc) (file_ptr->error, file_ptr->client_data);
 382           break;
 383         }
 384     }
 385 }
 386
 387 /* Create a file event, to be enqueued in the event queue for
 388    processing.  The procedure associated to this event is always
 389    handle_file_event, which will in turn invoke the one that was
 390    associated to FD when it was registered with the event loop.  */
 391
 392 static gdb_event *
 393 create_file_event (int fd)
 394 {
 395   gdb_event *file_event_ptr;
 396
 397   file_event_ptr = xmalloc (sizeof (gdb_event));
 398   file_event_ptr->proc = handle_file_event;
 399   file_event_ptr->fd = fd;
 400   return file_event_ptr;
 401 }
 402
 403 /* Called by do_one_event to wait for new events on the monitored file
 404    descriptors.  Queue file events as they are detected by the poll.
 405    If there are no events, this function will block in the call to
 406    select.  Return -1 if there are no files descriptors to monitor,
 407    otherwise return 0.  */
 408
 409 static int
 410 wait_for_event (void)
 411 {
 412   file_handler *file_ptr;
 413   gdb_event *file_event_ptr;
 414   int num_found = 0;
 415
 416   /* Make sure all output is done before getting another event.  */
 417   fflush (stdout);
 418   fflush (stderr);
 419
 420   if (gdb_notifier.num_fds == 0)
 421     return -1;
 422
 423   gdb_notifier.ready_masks[0] = gdb_notifier.check_masks[0];
 424   gdb_notifier.ready_masks[1] = gdb_notifier.check_masks[1];
 425   gdb_notifier.ready_masks[2] = gdb_notifier.check_masks[2];
 426   num_found = select (gdb_notifier.num_fds,
 427                       &gdb_notifier.ready_masks[0],
 428                       &gdb_notifier.ready_masks[1],
 429                       &gdb_notifier.ready_masks[2],
 430                       NULL);
 431
 432   /* Clear the masks after an error from select.  */
 433   if (num_found == -1)
 434     {
 435       FD_ZERO (&gdb_notifier.ready_masks[0]);
 436       FD_ZERO (&gdb_notifier.ready_masks[1]);
 437       FD_ZERO (&gdb_notifier.ready_masks[2]);
 438 #ifdef EINTR
 439       /* Dont print anything if we got a signal, let gdb handle
 440          it.  */
 441       if (errno != EINTR)
 442         perror_with_name ("select");
 443 #endif
 444     }
 445
 446   /* Enqueue all detected file events.  */
 447
 448   for (file_ptr = gdb_notifier.first_file_handler;
 449        file_ptr != NULL && num_found > 0;
 450        file_ptr = file_ptr->next_file)
 451     {
 452       int mask = 0;
 453
 454       if (FD_ISSET (file_ptr->fd, &gdb_notifier.ready_masks[0]))
 455         mask |= GDB_READABLE;
 456       if (FD_ISSET (file_ptr->fd, &gdb_notifier.ready_masks[1]))
 457         mask |= GDB_WRITABLE;
 458       if (FD_ISSET (file_ptr->fd, &gdb_notifier.ready_masks[2]))
 459         mask |= GDB_EXCEPTION;
 460
 461       if (!mask)
 462         continue;
 463       else
 464         num_found--;
 465
 466       /* Enqueue an event only if this is still a new event for this
 467          fd.  */
 468
 469       if (file_ptr->ready_mask == 0)
 470         {
 471           file_event_ptr = create_file_event (file_ptr->fd);
 472           async_queue_event (file_event_ptr);
 473         }
 474       file_ptr->ready_mask = mask;
 475     }
 476
 477   return 0;
 478 }
 479
 480 /* Start up the event loop.  This is the entry point to the event
 481    loop.  */
 482
 483 void
 484 start_event_loop (void)
 485 {
 486   /* Loop until there is nothing to do.  This is the entry point to
 487      the event loop engine.  If nothing is ready at this time, wait
 488      for something to happen (via wait_for_event), then process it.
 489      Return when there are no longer event sources to wait for.  */
 490
 491   while (1)
 492     {
 493       /* Any events already waiting in the queue?  */
 494       if (process_event ())
 495         continue;
 496
 497       /* Wait for a new event.  If wait_for_event returns -1, we
 498          should get out because this means that there are no event
 499          sources left.  This will make the event loop stop, and the
 500          application exit.  */
 501
 502       if (wait_for_event () < 0)
 503         return;
 504     }
 505
 506   /* We are done with the event loop.  There are no more event sources
 507      to listen to.  So we exit gdbserver.  */
 508 }