gdb/event-loop.c

   1 /* Event loop machinery for GDB, the GNU debugger.
   2    Copyright 1999 Free Software Foundation, Inc.
   3    Written by Elena Zannoni <ezannoni@cygnus.com> of Cygnus Solutions.
   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 2 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, write to the Free Software
  19    Foundation, Inc., 59 Temple Place - Suite 330,
  20    Boston, MA 02111-1307, USA. */
  21
  22 #include "defs.h"
  23 #include "top.h"
  24 #include "event-loop.h"
  25 #ifdef HAVE_POLL
  26 #include <poll.h>
  27 #else
  28 #include <sys/types.h>
  29 #endif
  30 #include <errno.h>
  31 #include <setjmp.h>
  32
  33 /* Event queue:
  34    - the first event in the queue is the head of the queue.
  35    It will be the next to be serviced.
  36    - the last event in the queue
  37
  38    Events can be inserted at the front of the queue or at the end of
  39    the queue.  Events will be extracted from the queue for processing
  40    starting from the head.  Therefore, events inserted at the head of
  41    the queue will be processed in a last in first out fashion, while
  42    those inserted at the tail of the queue will be processed in a first
  43    in first out manner.  All the fields are NULL if the queue is
  44    empty. */
  45
  46 static struct
  47   {
  48     gdb_event *first_event;     /* First pending event */
  49     gdb_event *last_event;      /* Last pending event */
  50   }
  51 event_queue;
  52
  53 /* Gdb_notifier is just a list of file descriptors gdb is interested in.
  54    These are the input file descriptor, and the target file
  55    descriptor. We have two flavors of the notifier, one for platforms
  56    that have the POLL function, the other for those that don't, and
  57    only support SELECT. Each of the elements in the gdb_notifier list is
  58    basically a description of what kind of events gdb is interested
  59    in, for each fd. */
  60
  61 /* As of 1999-04-30 only the input file descriptor is registered with the
  62    event loop. */
  63
  64 #ifdef HAVE_POLL
  65 /* Poll based implementation of the notifier. */
  66
  67 static struct
  68   {
  69     /* Ptr to head of file handler list. */
  70     file_handler *first_file_handler;
  71
  72     /* Ptr to array of pollfd structures. */
  73     struct pollfd *poll_fds;
  74
  75     /* Number of file descriptors to monitor. */
  76     int num_fds;
  77
  78   }
  79 gdb_notifier;
  80
  81 #else /* ! HAVE_POLL */
  82
  83 /* Select based implementation of the notifier. */
  84
  85 static struct
  86   {
  87     /* Ptr to head of file handler list. */
  88     file_handler *first_file_handler;
  89
  90     /* Masks to be used in the next call to select.
  91        Bits are set in response to calls to create_file_handler. */
  92     fd_mask check_masks[3 * MASK_SIZE];
  93
  94     /* What file descriptors were found ready by select. */
  95     fd_mask ready_masks[3 * MASK_SIZE];
  96
  97     /* Number of valid bits (highest fd value + 1). */
  98     int num_fds;
  99
 100   }
 101 gdb_notifier;
 102
 103 #endif /* HAVE_POLL */
 104
 105 /* All the async_signal_handlers gdb is interested in are kept onto
 106    this list. */
 107 static struct
 108   {
 109     /* Pointer to first in handler list. */
 110     async_signal_handler *first_handler;
 111
 112     /* Pointer to last in handler list. */
 113     async_signal_handler *last_handler;
 114   }
 115 sighandler_list;
 116
 117 /* Is any of the handlers ready?  Check this variable using
 118    check_async_ready. This is used by process_event, to determine
 119    whether or not to invoke the invoke_async_signal_handler
 120    function. */
 121 static int async_handler_ready = 0;
 122
 123 static void create_file_handler PARAMS ((int, int, file_handler_func *, gdb_client_data));
 124 static void invoke_async_signal_handler PARAMS ((void));
 125 static int gdb_wait_for_event PARAMS ((void));
 126 static int gdb_do_one_event PARAMS ((void));
 127 static int check_async_ready PARAMS ((void));
 128 \f
 129
 130 /* Insert an event object into the gdb event queue at
 131    the specified position.
 132    POSITION can be head or tail, with values TAIL, HEAD.
 133    EVENT_PTR points to the event to be inserted into the queue.
 134    The caller must allocate memory for the event. It is freed
 135    after the event has ben handled.
 136    Events in the queue will be processed head to tail, therefore,
 137    events inserted at the head of the queue will be processed
 138    as last in first out. Event appended at the tail of the queue
 139    will be processed first in first out. */
 140 static void
 141 async_queue_event (event_ptr, position)
 142      gdb_event *event_ptr;
 143      queue_position position;
 144 {
 145   if (position == TAIL)
 146     {
 147       /* The event will become the new last_event. */
 148
 149       event_ptr->next_event = NULL;
 150       if (event_queue.first_event == NULL)
 151         event_queue.first_event = event_ptr;
 152       else
 153         event_queue.last_event->next_event = event_ptr;
 154       event_queue.last_event = event_ptr;
 155     }
 156   else if (position == HEAD)
 157     {
 158       /* The event becomes the new first_event. */
 159
 160       event_ptr->next_event = event_queue.first_event;
 161       if (event_queue.first_event == NULL)
 162         event_queue.last_event = event_ptr;
 163       event_queue.first_event = event_ptr;
 164     }
 165 }
 166
 167 /* Process one event.
 168    The event can be the next one to be serviced in the event queue,
 169    or an asynchronous event handler can be invoked in response to
 170    the reception of a signal.
 171    If an event was processed (either way), 1 is returned otherwise
 172    0 is returned.
 173    Scan the queue from head to tail, processing therefore the high
 174    priority events first, by invoking the associated event handler
 175    procedure. */
 176 static int
 177 process_event ()
 178 {
 179   gdb_event *event_ptr, *prev_ptr;
 180   event_handler_func *proc;
 181   int fd;
 182
 183   /* First let's see if there are any asynchronous event handlers that
 184      are ready. These would be the result of invoking any of the
 185      signal handlers. */
 186
 187   if (check_async_ready ())
 188     {
 189       invoke_async_signal_handler ();
 190       return 1;
 191     }
 192
 193   /* Look in the event queue to find an event that is ready
 194      to be processed. */
 195
 196   for (event_ptr = event_queue.first_event; event_ptr != NULL;
 197        event_ptr = event_ptr->next_event)
 198     {
 199       /* Call the handler for the event. */
 200
 201       proc = event_ptr->proc;
 202       fd = event_ptr->fd;
 203
 204       /* Let's get rid of the event from the event queue.  We need to
 205          do this now because while processing the event, the proc
 206          function could end up calling 'error' and therefore jump out
 207          to the caller of this function, gdb_do_one_event. In that
 208          case, we would have on the event queue an event wich has been
 209          processed, but not deleted. */
 210
 211       if (event_queue.first_event == event_ptr)
 212         {
 213           event_queue.first_event = event_ptr->next_event;
 214           if (event_ptr->next_event == NULL)
 215             event_queue.last_event = NULL;
 216         }
 217       else
 218         {
 219           prev_ptr = event_queue.first_event;
 220           while (prev_ptr->next_event != event_ptr)
 221             prev_ptr = prev_ptr->next_event;
 222
 223           prev_ptr->next_event = event_ptr->next_event;
 224           if (event_ptr->next_event == NULL)
 225             event_queue.last_event = prev_ptr;
 226         }
 227       free ((char *) event_ptr);
 228
 229       /* Now call the procedure associted with the event. */
 230       (*proc) (fd);
 231       return 1;
 232     }
 233
 234   /* this is the case if there are no event on the event queue. */
 235   return 0;
 236 }
 237
 238 /* Process one high level event.  If nothing is ready at this time,
 239    wait for something to happen (via gdb_wait_for_event), then process
 240    it.  Returns 1 if something was done otherwise returns 0 (this can
 241    happen if there are no event sources to wait for). */
 242 static int
 243 gdb_do_one_event ()
 244 {
 245   int result = 0;
 246
 247   while (1)
 248     {
 249       if (!SET_TOP_LEVEL ())
 250         {
 251           /* Any events already waiting in the queue? */
 252           if (process_event ())
 253             {
 254               result = 1;
 255               break;
 256             }
 257
 258           /* Wait for a new event.  If gdb_wait_for_event returns -1,
 259              we should get out because this means that there are no
 260              event sources left. This will make the event loop stop,
 261              and the application exit. */
 262
 263           result = gdb_wait_for_event ();
 264           if (result < 0)
 265             {
 266               result = 0;
 267               break;
 268             }
 269
 270           /* Handle any new events occurred while waiting. */
 271           if (process_event ())
 272             {
 273               result = 1;
 274               break;
 275             }
 276
 277           /* If gdb_wait_for_event has returned 1, it means that one
 278              event has been handled. We break out of the loop. */
 279           if (result)
 280             break;
 281         }                       /* end of if !set_top_level */
 282       else
 283         {
 284           /* FIXME: this should really be a call to a hook that is
 285              interface specific, because interfaces can display the
 286              prompt in their own way. */
 287           display_gdb_prompt (0);
 288           /* Maybe better to set a flag to be checked somewhere as to
 289              whether display the prompt or not. */
 290         }
 291     }
 292   return result;
 293 }
 294 \f
 295
 296 /* Start up the event loop. This is the entry point to the event loop
 297    from the command loop. */
 298 void
 299 start_event_loop ()
 300 {
 301   /* Loop until there is something to do. This is the entry point to
 302      the event loop engine. gdb_do_one_event will process one event
 303      for each invocation.  It always returns 1, unless there are no
 304      more event sources registered. In this case it returns 0.  */
 305   while (gdb_do_one_event () != 0)
 306     ;
 307
 308   /* We are done with the event loop. There are no more event sources
 309      to listen to.  So we exit GDB. */
 310   return;
 311 }
 312 \f
 313
 314
 315 /* Wrapper function for create_file_handler, so that the caller
 316    doesn't have to know implementation details about the use of poll
 317    vs. select. */
 318 void
 319 add_file_handler (fd, proc, client_data)
 320      int fd;
 321      file_handler_func *proc;
 322      gdb_client_data client_data;
 323 {
 324 #ifdef HAVE_POLL
 325   create_file_handler (fd, POLLIN, (file_handler_func *) proc, client_data);
 326 #else
 327   create_file_handler (fd, GDB_READABLE, (file_handler_func *) proc, client_data);
 328 #endif
 329 }
 330
 331 /* Add a file handler/descriptor to the list of descriptors we are
 332    interested in.
 333    FD is the file descriptor for the file/stream to be listened to.
 334    For the poll case, MASK is a combination (OR) of
 335    POLLIN, POLLRDNORM, POLLRDBAND, POLLPRI, POLLOUT, POLLWRNORM,
 336    POLLWRBAND: these are the events we are interested in. If any of them
 337    occurs, proc should be called.
 338    For the select case, MASK is a combination of READABLE, WRITABLE, EXCEPTION.
 339    PROC is the procedure that will be called when an event occurs for
 340    FD.  CLIENT_DATA is the argument to pass to PROC. */
 341 static void
 342 create_file_handler (fd, mask, proc, client_data)
 343      int fd;
 344      int mask;
 345      file_handler_func *proc;
 346      gdb_client_data client_data;
 347 {
 348   file_handler *file_ptr;
 349
 350 #ifndef HAVE_POLL
 351   int index, bit;
 352 #endif
 353
 354   /* Do we already have a file handler for this file? (We may be
 355      changing its associated procedure). */
 356   for (file_ptr = gdb_notifier.first_file_handler; file_ptr != NULL;
 357        file_ptr = file_ptr->next_file)
 358     {
 359       if (file_ptr->fd == fd)
 360         break;
 361     }
 362
 363   /* It is a new file descriptor. */
 364   if (file_ptr == NULL)
 365     {
 366       file_ptr = (file_handler *) xmalloc (sizeof (file_handler));
 367       file_ptr->fd = fd;
 368       file_ptr->ready_mask = 0;
 369       file_ptr->next_file = gdb_notifier.first_file_handler;
 370       gdb_notifier.first_file_handler = file_ptr;
 371     }
 372   file_ptr->proc = proc;
 373   file_ptr->client_data = client_data;
 374   file_ptr->mask = mask;
 375
 376 #ifdef HAVE_POLL
 377
 378   gdb_notifier.num_fds++;
 379   if (gdb_notifier.poll_fds)
 380     gdb_notifier.poll_fds =
 381       (struct pollfd *) realloc (gdb_notifier.poll_fds,
 382                            (gdb_notifier.num_fds) * sizeof (struct pollfd));
 383   else
 384     gdb_notifier.poll_fds =
 385       (struct pollfd *) xmalloc (sizeof (struct pollfd));
 386   (gdb_notifier.poll_fds + gdb_notifier.num_fds - 1)->fd = fd;
 387   (gdb_notifier.poll_fds + gdb_notifier.num_fds - 1)->events = mask;
 388   (gdb_notifier.poll_fds + gdb_notifier.num_fds - 1)->revents = 0;
 389
 390 #else /* ! HAVE_POLL */
 391
 392   index = fd / (NBBY * sizeof (fd_mask));
 393   bit = 1 << (fd % (NBBY * sizeof (fd_mask)));
 394
 395   if (mask & GDB_READABLE)
 396     gdb_notifier.check_masks[index] |= bit;
 397   else
 398     gdb_notifier.check_masks[index] &= ~bit;
 399
 400   if (mask & GDB_WRITABLE)
 401     (gdb_notifier.check_masks + MASK_SIZE)[index] |= bit;
 402   else
 403     (gdb_notifier.check_masks + MASK_SIZE)[index] &= ~bit;
 404
 405   if (mask & GDB_EXCEPTION)
 406     (gdb_notifier.check_masks + 2 * (MASK_SIZE))[index] |= bit;
 407   else
 408     (gdb_notifier.check_masks + 2 * (MASK_SIZE))[index] &= ~bit;
 409
 410   if (gdb_notifier.num_fds <= fd)
 411     gdb_notifier.num_fds = fd + 1;
 412
 413 #endif /* HAVE_POLL */
 414 }
 415
 416 /* Remove the file descriptor FD from the list of monitored fd's:
 417    i.e. we don't care anymore about events on the FD. */
 418 void
 419 delete_file_handler (fd)
 420      int fd;
 421 {
 422   file_handler *file_ptr, *prev_ptr = NULL;
 423   int i, j;
 424   struct pollfd *new_poll_fds;
 425 #ifndef HAVE_POLL
 426   int index, bit;
 427   unsigned long flags;
 428 #endif
 429
 430   /* Find the entry for the given file. */
 431
 432   for (file_ptr = gdb_notifier.first_file_handler; file_ptr != NULL;
 433        file_ptr = file_ptr->next_file)
 434     {
 435       if (file_ptr->fd == fd)
 436         break;
 437     }
 438
 439   if (file_ptr == NULL)
 440     return;
 441
 442   /* Deactivate the file descriptor, by clearing its mask,
 443      so that it will not fire again. */
 444
 445   file_ptr->mask = 0;
 446
 447 #ifdef HAVE_POLL
 448   /* Create a new poll_fds array by copying every fd's information but the
 449      one we want to get rid of. */
 450
 451   new_poll_fds =
 452     (struct pollfd *) xmalloc ((gdb_notifier.num_fds - 1) * sizeof (struct pollfd));
 453
 454   for (i = 0, j = 0; i < gdb_notifier.num_fds; i++)
 455     {
 456       if ((gdb_notifier.poll_fds + i)->fd != fd)
 457         {
 458           (new_poll_fds + j)->fd = (gdb_notifier.poll_fds + i)->fd;
 459           (new_poll_fds + j)->events = (gdb_notifier.poll_fds + i)->events;
 460           (new_poll_fds + j)->revents = (gdb_notifier.poll_fds + i)->revents;
 461           j++;
 462         }
 463     }
 464   free (gdb_notifier.poll_fds);
 465   gdb_notifier.poll_fds = new_poll_fds;
 466   gdb_notifier.num_fds--;
 467
 468 #else /* ! HAVE_POLL */
 469
 470   index = fd / (NBBY * sizeof (fd_mask));
 471   bit = 1 << (fd % (NBBY * sizeof (fd_mask)));
 472
 473   if (file_ptr->mask & GDB_READABLE)
 474     gdb_notifier.check_masks[index] &= ~bit;
 475   if (file_ptr->mask & GDB_WRITABLE)
 476     (gdb_notifier.check_masks + MASK_SIZE)[index] &= ~bit;
 477   if (file_ptr->mask & GDB_EXCEPTION)
 478     (gdb_notifier.check_masks + 2 * (MASK_SIZE))[index] &= ~bit;
 479
 480   /* Find current max fd. */
 481
 482   if ((fd + 1) == gdb_notifier.num_fds)
 483     {
 484       for (gdb_notifier.num_fds = 0; index >= 0; index--)
 485         {
 486           flags = gdb_notifier.check_masks[index]
 487             | (gdb_notifier.check_masks + MASK_SIZE)[index]
 488             | (gdb_notifier.check_masks + 2 * (MASK_SIZE))[index];
 489           if (flags)
 490             {
 491               for (i = (NBBY * sizeof (fd_mask)); i > 0; i--)
 492                 {
 493                   if (flags & (((unsigned long) 1) << (i - 1)))
 494                     break;
 495                 }
 496               gdb_notifier.num_fds = index * (NBBY * sizeof (fd_mask)) + i;
 497               break;
 498             }
 499         }
 500     }
 501 #endif /* HAVE_POLL */
 502
 503   /* Get rid of the file handler in the file handler list. */
 504   if (file_ptr == gdb_notifier.first_file_handler)
 505     gdb_notifier.first_file_handler = file_ptr->next_file;
 506   else
 507     {
 508       for (prev_ptr = gdb_notifier.first_file_handler;
 509            prev_ptr->next_file != file_ptr;
 510            prev_ptr = prev_ptr->next_file)
 511         ;
 512       prev_ptr->next_file = file_ptr->next_file;
 513     }
 514   free ((char *) file_ptr);
 515 }
 516
 517 /* Handle the given event by calling the procedure associated to the
 518    corresponding file handler.  Called by process_event indirectly,
 519    through event_ptr->proc.  EVENT_FILE_DESC is file descriptor of the
 520    event in the front of the event queue. */
 521 static void
 522 handle_file_event (event_file_desc)
 523      int event_file_desc;
 524 {
 525   file_handler *file_ptr;
 526   int mask, error_mask;
 527
 528   /* Search the file handler list to find one that matches the fd in
 529      the event. */
 530   for (file_ptr = gdb_notifier.first_file_handler; file_ptr != NULL;
 531        file_ptr = file_ptr->next_file)
 532     {
 533       if (file_ptr->fd == event_file_desc)
 534         {
 535           /* With poll, the ready_mask could have any of three events
 536              set to 1: POLLHUP, POLLERR, POLLNVAL. These events cannot
 537              be used in the requested event mask (events), but they
 538              can be returned in the return mask (revents). We need to
 539              check for those event too, and add them to the mask which
 540              will be passed to the handler. */
 541
 542           /* See if the desired events (mask) match the received
 543              events (ready_mask). */
 544
 545 #ifdef HAVE_POLL
 546           error_mask = POLLHUP | POLLERR | POLLNVAL;
 547           mask = (file_ptr->ready_mask & file_ptr->mask) |
 548             (file_ptr->ready_mask & error_mask);
 549
 550 #else /* ! HAVE_POLL */
 551           mask = file_ptr->ready_mask & file_ptr->mask;
 552 #endif /* HAVE_POLL */
 553
 554           /* Clear the received events for next time around. */
 555           file_ptr->ready_mask = 0;
 556
 557           /* If there was a match, then call the handler. */
 558           if (mask != 0)
 559             (*file_ptr->proc) (file_ptr->client_data, mask);
 560           break;
 561         }
 562     }
 563 }
 564
 565 /* Called by gdb_do_one_event to wait for new events on the
 566    monitored file descriptors. Queue file events as they are
 567    detected by the poll.
 568    If there are no events, this function will block in the
 569    call to poll.
 570    Return -1 if there are no files descriptors to monitor,
 571    otherwise return 0. */
 572 static int
 573 gdb_wait_for_event ()
 574 {
 575   file_handler *file_ptr;
 576   gdb_event *file_event_ptr;
 577   int num_found = 0;
 578   int i;
 579
 580 #ifndef HAVE_POLL
 581   int mask, bit, index;
 582 #endif
 583
 584   if (gdb_notifier.num_fds == 0)
 585     return -1;
 586
 587 #ifdef HAVE_POLL
 588   num_found =
 589     poll (gdb_notifier.poll_fds, (unsigned long) gdb_notifier.num_fds, -1);
 590
 591 #else /* ! HAVE_POLL */
 592   memcpy (gdb_notifier.ready_masks,
 593           gdb_notifier.check_masks,
 594           3 * MASK_SIZE * sizeof (fd_mask));
 595   num_found = select (gdb_notifier.num_fds,
 596                       (SELECT_MASK *) & gdb_notifier.ready_masks[0],
 597                       (SELECT_MASK *) & gdb_notifier.ready_masks[MASK_SIZE],
 598                   (SELECT_MASK *) & gdb_notifier.ready_masks[2 * MASK_SIZE],
 599                       NULL);
 600
 601   /* Clear the masks after an error from select. */
 602   if (num_found == -1)
 603     memset (gdb_notifier.ready_masks,
 604             0, 3 * MASK_SIZE * sizeof (fd_mask));
 605
 606 #endif /* HAVE_POLL */
 607
 608   /* Enqueue all detected file events. */
 609
 610 #ifdef HAVE_POLL
 611
 612   for (i = 0; (i < gdb_notifier.num_fds) && (num_found > 0); i++)
 613     {
 614       if ((gdb_notifier.poll_fds + i)->revents)
 615         num_found--;
 616       else
 617         continue;
 618
 619       for (file_ptr = gdb_notifier.first_file_handler;
 620            file_ptr != NULL;
 621            file_ptr = file_ptr->next_file)
 622         {
 623           if (file_ptr->fd == (gdb_notifier.poll_fds + i)->fd)
 624             break;
 625         }
 626
 627       if (file_ptr)
 628         {
 629           /* Enqueue an event only if this is still a new event for
 630              this fd. */
 631           if (file_ptr->ready_mask == 0)
 632             {
 633               file_event_ptr =
 634                 (gdb_event *) xmalloc (sizeof (gdb_event));
 635               file_event_ptr->proc = handle_file_event;
 636               file_event_ptr->fd = file_ptr->fd;
 637               async_queue_event (file_event_ptr, TAIL);
 638             }
 639         }
 640
 641       file_ptr->ready_mask = (gdb_notifier.poll_fds + i)->revents;
 642     }
 643
 644 #else /* ! HAVE_POLL */
 645   for (file_ptr = gdb_notifier.first_file_handler;
 646        (file_ptr != NULL) && (num_found > 0);
 647        file_ptr = file_ptr->next_file)
 648     {
 649       index = file_ptr->fd / (NBBY * sizeof (fd_mask));
 650       bit = 1 << (file_ptr->fd % (NBBY * sizeof (fd_mask)));
 651       mask = 0;
 652
 653       if (gdb_notifier.ready_masks[index] & bit)
 654         mask |= GDB_READABLE;
 655       if ((gdb_notifier.ready_masks + MASK_SIZE)[index] & bit)
 656         mask |= GDB_WRITABLE;
 657       if ((gdb_notifier.ready_masks + 2 * (MASK_SIZE))[index] & bit)
 658         mask |= GDB_EXCEPTION;
 659
 660       if (!mask)
 661         continue;
 662       else
 663         num_found--;
 664
 665       /* Enqueue an event only if this is still a new event for
 666          this fd. */
 667
 668       if (file_ptr->ready_mask == 0)
 669         {
 670           file_event_ptr =
 671             (gdb_event *) xmalloc (sizeof (gdb_event));
 672           file_event_ptr->proc = handle_file_event;
 673           file_event_ptr->fd = file_ptr->fd;
 674           async_queue_event (file_event_ptr, TAIL);
 675         }
 676       file_ptr->ready_mask = mask;
 677     }
 678 #endif /* HAVE_POLL */
 679
 680   return 0;
 681 }
 682 \f
 683
 684 /* Create an asynchronous handler, allocating memory for it.
 685    Return a pointer to the newly created handler.
 686    This pointer will be used to invoke the handler by
 687    invoke_async_signal_handler.
 688    PROC is the function to call with CLIENT_DATA argument
 689    whenever the handler is invoked. */
 690 async_signal_handler *
 691 create_async_signal_handler (proc, client_data)
 692      async_handler_func *proc;
 693      gdb_client_data client_data;
 694 {
 695   async_signal_handler *async_handler_ptr;
 696
 697   async_handler_ptr =
 698     (async_signal_handler *) xmalloc (sizeof (async_signal_handler));
 699   async_handler_ptr->ready = 0;
 700   async_handler_ptr->next_handler = NULL;
 701   async_handler_ptr->proc = proc;
 702   async_handler_ptr->client_data = client_data;
 703   if (sighandler_list.first_handler == NULL)
 704     sighandler_list.first_handler = async_handler_ptr;
 705   else
 706     sighandler_list.last_handler->next_handler = async_handler_ptr;
 707   sighandler_list.last_handler = async_handler_ptr;
 708   return async_handler_ptr;
 709 }
 710
 711 /* Mark the handler (ASYNC_HANDLER_PTR) as ready. This information will
 712    be used when the handlers are invoked, after we have waited for
 713    some event.  The caller of this function is the interrupt handler
 714    associated with a signal. */
 715 void
 716 mark_async_signal_handler (async_handler_ptr)
 717      async_signal_handler *async_handler_ptr;
 718 {
 719   ((async_signal_handler *) async_handler_ptr)->ready = 1;
 720   async_handler_ready = 1;
 721 }
 722
 723 /* Call all the handlers that are ready. */
 724 static void
 725 invoke_async_signal_handler ()
 726 {
 727   async_signal_handler *async_handler_ptr;
 728
 729   if (async_handler_ready == 0)
 730     return;
 731   async_handler_ready = 0;
 732
 733   /* Invoke ready handlers. */
 734
 735   while (1)
 736     {
 737       for (async_handler_ptr = sighandler_list.first_handler;
 738            async_handler_ptr != NULL;
 739            async_handler_ptr = async_handler_ptr->next_handler)
 740         {
 741           if (async_handler_ptr->ready)
 742             break;
 743         }
 744       if (async_handler_ptr == NULL)
 745         break;
 746       async_handler_ptr->ready = 0;
 747       (*async_handler_ptr->proc) (async_handler_ptr->client_data);
 748     }
 749
 750   return;
 751 }
 752
 753 /* Delete an asynchronous handler (ASYNC_HANDLER_PTR).
 754    Free the space allocated for it.  */
 755 void
 756 delete_async_signal_handler (async_handler_ptr)
 757      async_signal_handler **async_handler_ptr;
 758 {
 759   async_signal_handler *prev_ptr;
 760
 761   if (sighandler_list.first_handler == (*async_handler_ptr))
 762     {
 763       sighandler_list.first_handler = (*async_handler_ptr)->next_handler;
 764       if (sighandler_list.first_handler == NULL)
 765         sighandler_list.last_handler = NULL;
 766     }
 767   else
 768     {
 769       prev_ptr = sighandler_list.first_handler;
 770       while (prev_ptr->next_handler != (*async_handler_ptr) && prev_ptr)
 771         prev_ptr = prev_ptr->next_handler;
 772       prev_ptr->next_handler = (*async_handler_ptr)->next_handler;
 773       if (sighandler_list.last_handler == (*async_handler_ptr))
 774         sighandler_list.last_handler = prev_ptr;
 775     }
 776   free ((char *) (*async_handler_ptr));
 777   (*async_handler_ptr) = NULL;
 778 }
 779
 780 /* Is it necessary to call invoke_async_signal_handler? */
 781 static int
 782 check_async_ready ()
 783 {
 784   return async_handler_ready;
 785 }