aboutsummaryrefslogtreecommitdiff
path: root/gdbsupport/event-loop.cc
blob: b1a5c1ad4399613352efb0b9db871ae209d78858 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
/* Event loop machinery for GDB, the GNU debugger.
   Copyright (C) 1999-2022 Free Software Foundation, Inc.
   Written by Elena Zannoni <ezannoni@cygnus.com> of Cygnus Solutions.

   This file is part of GDB.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */

#include "gdbsupport/common-defs.h"
#include "gdbsupport/event-loop.h"

#include <chrono>

#ifdef HAVE_POLL
#if defined (HAVE_POLL_H)
#include <poll.h>
#elif defined (HAVE_SYS_POLL_H)
#include <sys/poll.h>
#endif
#endif

#include <sys/types.h>
#include "gdbsupport/gdb_sys_time.h"
#include "gdbsupport/gdb_select.h"
#include "gdbsupport/gdb_optional.h"
#include "gdbsupport/scope-exit.h"

/* See event-loop.h.  */

debug_event_loop_kind debug_event_loop;

/* Tell create_file_handler what events we are interested in.
   This is used by the select version of the event loop.  */

#define GDB_READABLE	(1<<1)
#define GDB_WRITABLE	(1<<2)
#define GDB_EXCEPTION	(1<<3)

/* Information about each file descriptor we register with the event
   loop.  */

struct file_handler
{
  /* File descriptor.  */
  int fd;

  /* Events we want to monitor: POLLIN, etc.  */
  int mask;

  /* Events that have been seen since the last time.  */
  int ready_mask;

  /* Procedure to call when fd is ready.  */
  handler_func *proc;

  /* Argument to pass to proc.  */
  gdb_client_data client_data;

  /* User-friendly name of this handler.  */
  std::string name;

  /* If set, this file descriptor is used for a user interface.  */
  bool is_ui;

  /* Was an error detected on this fd?  */
  int error;

  /* Next registered file descriptor.  */
  struct file_handler *next_file;
};

#ifdef HAVE_POLL
/* Do we use poll or select?  Some systems have poll, but then it's
   not useable with all kinds of files.  We probe that whenever a new
   file handler is added.  */
static bool use_poll = true;
#endif

#ifdef USE_WIN32API
#include <windows.h>
#include <io.h>
#endif

/* Gdb_notifier is just a list of file descriptors gdb is interested in.
   These are the input file descriptor, and the target file
   descriptor.  We have two flavors of the notifier, one for platforms
   that have the POLL function, the other for those that don't, and
   only support SELECT.  Each of the elements in the gdb_notifier list is
   basically a description of what kind of events gdb is interested
   in, for each fd.  */

static struct
  {
    /* Ptr to head of file handler list.  */
    file_handler *first_file_handler;

    /* Next file handler to handle, for the select variant.  To level
       the fairness across event sources, we serve file handlers in a
       round-robin-like fashion.  The number and order of the polled
       file handlers may change between invocations, but this is good
       enough.  */
    file_handler *next_file_handler;

#ifdef HAVE_POLL
    /* Ptr to array of pollfd structures.  */
    struct pollfd *poll_fds;

    /* Next file descriptor to handle, for the poll variant.  To level
       the fairness across event sources, we poll the file descriptors
       in a round-robin-like fashion.  The number and order of the
       polled file descriptors may change between invocations, but
       this is good enough.  */
    int next_poll_fds_index;

    /* Timeout in milliseconds for calls to poll().  */
    int poll_timeout;
#endif

    /* Masks to be used in the next call to select.
       Bits are set in response to calls to create_file_handler.  */
    fd_set check_masks[3];

    /* What file descriptors were found ready by select.  */
    fd_set ready_masks[3];

    /* Number of file descriptors to monitor (for poll).  */
    /* Number of valid bits (highest fd value + 1) (for select).  */
    int num_fds;

    /* Time structure for calls to select().  */
    struct timeval select_timeout;

    /* Flag to tell whether the timeout should be used.  */
    int timeout_valid;
  }
gdb_notifier;

/* Structure associated with a timer.  PROC will be executed at the
   first occasion after WHEN.  */
struct gdb_timer
  {
    std::chrono::steady_clock::time_point when;
    int timer_id;
    struct gdb_timer *next;
    timer_handler_func *proc;	    /* Function to call to do the work.  */
    gdb_client_data client_data;    /* Argument to async_handler_func.  */
  };

/* List of currently active timers.  It is sorted in order of
   increasing timers.  */
static struct
  {
    /* Pointer to first in timer list.  */
    struct gdb_timer *first_timer;

    /* Id of the last timer created.  */
    int num_timers;
  }
timer_list;

static void create_file_handler (int fd, int mask, handler_func *proc,
				 gdb_client_data client_data,
				 std::string &&name, bool is_ui);
static int gdb_wait_for_event (int);
static int update_wait_timeout (void);
static int poll_timers (void);

/* Process one high level event.  If nothing is ready at this time,
   wait at most MSTIMEOUT milliseconds for something to happen (via
   gdb_wait_for_event), then process it.  Returns >0 if something was
   done, <0 if there are no event sources to wait for, =0 if timeout occurred.
   A timeout of 0 allows to serve an already pending event, but does not
   wait if none found.
   Setting the timeout to a negative value disables it.
   The timeout is never used by gdb itself, it is however needed to
   integrate gdb event handling within Insight's GUI event loop. */

int
gdb_do_one_event (int mstimeout)
{
  static int event_source_head = 0;
  const int number_of_sources = 3;
  int current = 0;

  /* First let's see if there are any asynchronous signal handlers
     that are ready.  These would be the result of invoking any of the
     signal handlers.  */
  if (invoke_async_signal_handlers ())
    return 1;

  /* To level the fairness across event sources, we poll them in a
     round-robin fashion.  */
  for (current = 0; current < number_of_sources; current++)
    {
      int res;

      switch (event_source_head)
	{
	case 0:
	  /* Are any timers that are ready?  */
	  res = poll_timers ();
	  break;
	case 1:
	  /* Are there events already waiting to be collected on the
	     monitored file descriptors?  */
	  res = gdb_wait_for_event (0);
	  break;
	case 2:
	  /* Are there any asynchronous event handlers ready?  */
	  res = check_async_event_handlers ();
	  break;
	default:
	  internal_error ("unexpected event_source_head %d",
			  event_source_head);
	}

      event_source_head++;
      if (event_source_head == number_of_sources)
	event_source_head = 0;

      if (res > 0)
	return 1;
    }

  if (mstimeout == 0)
    return 0;	/* 0ms timeout: do not wait for an event. */

  /* Block waiting for a new event.  If gdb_wait_for_event returns -1,
     we should get out because this means that there are no event
     sources left.  This will make the event loop stop, and the
     application exit.
     If a timeout has been given, a new timer is set accordingly
     to abort event wait.  It is deleted upon gdb_wait_for_event
     termination and thus should never be triggered.
     When the timeout is reached, events are not monitored again:
     they already have been checked in the loop above. */

  gdb::optional<int> timer_id;

  SCOPE_EXIT 
    {
      if (timer_id.has_value ())
	delete_timer (*timer_id);
    };

  if (mstimeout > 0)
    timer_id = create_timer (mstimeout,
			     [] (gdb_client_data arg)
			     {
			       ((gdb::optional<int> *) arg)->reset ();
			     },
			     &timer_id);
  return gdb_wait_for_event (1);
}

/* See event-loop.h  */

void
add_file_handler (int fd, handler_func *proc, gdb_client_data client_data,
		  std::string &&name, bool is_ui)
{
#ifdef HAVE_POLL
  if (use_poll)
    {
      struct pollfd fds;

      /* Check to see if poll () is usable.  If not, we'll switch to
	 use select.  This can happen on systems like
	 m68k-motorola-sys, `poll' cannot be used to wait for `stdin'.
	 On m68k-motorola-sysv, tty's are not stream-based and not
	 `poll'able.  */
      fds.fd = fd;
      fds.events = POLLIN;
      if (poll (&fds, 1, 0) == 1 && (fds.revents & POLLNVAL))
	use_poll = false;
    }
  if (use_poll)
    {
      create_file_handler (fd, POLLIN, proc, client_data, std::move (name),
			   is_ui);
    }
  else
#endif /* HAVE_POLL */
    create_file_handler (fd, GDB_READABLE | GDB_EXCEPTION,
			 proc, client_data, std::move (name), is_ui);
}

/* Helper for add_file_handler.

   For the poll case, MASK is a combination (OR) of POLLIN,
   POLLRDNORM, POLLRDBAND, POLLPRI, POLLOUT, POLLWRNORM, POLLWRBAND:
   these are the events we are interested in.  If any of them occurs,
   proc should be called.

   For the select case, MASK is a combination of READABLE, WRITABLE,
   EXCEPTION.  PROC is the procedure that will be called when an event
   occurs for FD.  CLIENT_DATA is the argument to pass to PROC.  */

static void
create_file_handler (int fd, int mask, handler_func * proc,
		     gdb_client_data client_data, std::string &&name,
		     bool is_ui)
{
  file_handler *file_ptr;

  /* Do we already have a file handler for this file?  (We may be
     changing its associated procedure).  */
  for (file_ptr = gdb_notifier.first_file_handler; file_ptr != NULL;
       file_ptr = file_ptr->next_file)
    {
      if (file_ptr->fd == fd)
	break;
    }

  /* It is a new file descriptor.  Add it to the list.  Otherwise, just
     change the data associated with it.  */
  if (file_ptr == NULL)
    {
      file_ptr = new file_handler;
      file_ptr->fd = fd;
      file_ptr->ready_mask = 0;
      file_ptr->next_file = gdb_notifier.first_file_handler;
      gdb_notifier.first_file_handler = file_ptr;

#ifdef HAVE_POLL
      if (use_poll)
	{
	  gdb_notifier.num_fds++;
	  if (gdb_notifier.poll_fds)
	    gdb_notifier.poll_fds =
	      (struct pollfd *) xrealloc (gdb_notifier.poll_fds,
					  (gdb_notifier.num_fds
					   * sizeof (struct pollfd)));
	  else
	    gdb_notifier.poll_fds =
	      XNEW (struct pollfd);
	  (gdb_notifier.poll_fds + gdb_notifier.num_fds - 1)->fd = fd;
	  (gdb_notifier.poll_fds + gdb_notifier.num_fds - 1)->events = mask;
	  (gdb_notifier.poll_fds + gdb_notifier.num_fds - 1)->revents = 0;
	}
      else
#endif /* HAVE_POLL */
	{
	  if (mask & GDB_READABLE)
	    FD_SET (fd, &gdb_notifier.check_masks[0]);
	  else
	    FD_CLR (fd, &gdb_notifier.check_masks[0]);

	  if (mask & GDB_WRITABLE)
	    FD_SET (fd, &gdb_notifier.check_masks[1]);
	  else
	    FD_CLR (fd, &gdb_notifier.check_masks[1]);

	  if (mask & GDB_EXCEPTION)
	    FD_SET (fd, &gdb_notifier.check_masks[2]);
	  else
	    FD_CLR (fd, &gdb_notifier.check_masks[2]);

	  if (gdb_notifier.num_fds <= fd)
	    gdb_notifier.num_fds = fd + 1;
	}
    }

  file_ptr->proc = proc;
  file_ptr->client_data = client_data;
  file_ptr->mask = mask;
  file_ptr->name = std::move (name);
  file_ptr->is_ui = is_ui;
}

/* Return the next file handler to handle, and advance to the next
   file handler, wrapping around if the end of the list is
   reached.  */

static file_handler *
get_next_file_handler_to_handle_and_advance (void)
{
  file_handler *curr_next;

  /* The first time around, this is still NULL.  */
  if (gdb_notifier.next_file_handler == NULL)
    gdb_notifier.next_file_handler = gdb_notifier.first_file_handler;

  curr_next = gdb_notifier.next_file_handler;
  gdb_assert (curr_next != NULL);

  /* Advance.  */
  gdb_notifier.next_file_handler = curr_next->next_file;
  /* Wrap around, if necessary.  */
  if (gdb_notifier.next_file_handler == NULL)
    gdb_notifier.next_file_handler = gdb_notifier.first_file_handler;

  return curr_next;
}

/* Remove the file descriptor FD from the list of monitored fd's: 
   i.e. we don't care anymore about events on the FD.  */
void
delete_file_handler (int fd)
{
  file_handler *file_ptr, *prev_ptr = NULL;
  int i;

  /* Find the entry for the given file.  */

  for (file_ptr = gdb_notifier.first_file_handler; file_ptr != NULL;
       file_ptr = file_ptr->next_file)
    {
      if (file_ptr->fd == fd)
	break;
    }

  if (file_ptr == NULL)
    return;

#ifdef HAVE_POLL
  if (use_poll)
    {
      int j;
      struct pollfd *new_poll_fds;

      /* Create a new poll_fds array by copying every fd's information
	 but the one we want to get rid of.  */

      new_poll_fds = (struct pollfd *) 
	xmalloc ((gdb_notifier.num_fds - 1) * sizeof (struct pollfd));

      for (i = 0, j = 0; i < gdb_notifier.num_fds; i++)
	{
	  if ((gdb_notifier.poll_fds + i)->fd != fd)
	    {
	      (new_poll_fds + j)->fd = (gdb_notifier.poll_fds + i)->fd;
	      (new_poll_fds + j)->events = (gdb_notifier.poll_fds + i)->events;
	      (new_poll_fds + j)->revents
		= (gdb_notifier.poll_fds + i)->revents;
	      j++;
	    }
	}
      xfree (gdb_notifier.poll_fds);
      gdb_notifier.poll_fds = new_poll_fds;
      gdb_notifier.num_fds--;
    }
  else
#endif /* HAVE_POLL */
    {
      if (file_ptr->mask & GDB_READABLE)
	FD_CLR (fd, &gdb_notifier.check_masks[0]);
      if (file_ptr->mask & GDB_WRITABLE)
	FD_CLR (fd, &gdb_notifier.check_masks[1]);
      if (file_ptr->mask & GDB_EXCEPTION)
	FD_CLR (fd, &gdb_notifier.check_masks[2]);

      /* Find current max fd.  */

      if ((fd + 1) == gdb_notifier.num_fds)
	{
	  gdb_notifier.num_fds--;
	  for (i = gdb_notifier.num_fds; i; i--)
	    {
	      if (FD_ISSET (i - 1, &gdb_notifier.check_masks[0])
		  || FD_ISSET (i - 1, &gdb_notifier.check_masks[1])
		  || FD_ISSET (i - 1, &gdb_notifier.check_masks[2]))
		break;
	    }
	  gdb_notifier.num_fds = i;
	}
    }

  /* Deactivate the file descriptor, by clearing its mask, 
     so that it will not fire again.  */

  file_ptr->mask = 0;

  /* If this file handler was going to be the next one to be handled,
     advance to the next's next, if any.  */
  if (gdb_notifier.next_file_handler == file_ptr)
    {
      if (file_ptr->next_file == NULL
	  && file_ptr == gdb_notifier.first_file_handler)
	gdb_notifier.next_file_handler = NULL;
      else
	get_next_file_handler_to_handle_and_advance ();
    }

  /* Get rid of the file handler in the file handler list.  */
  if (file_ptr == gdb_notifier.first_file_handler)
    gdb_notifier.first_file_handler = file_ptr->next_file;
  else
    {
      for (prev_ptr = gdb_notifier.first_file_handler;
	   prev_ptr->next_file != file_ptr;
	   prev_ptr = prev_ptr->next_file)
	;
      prev_ptr->next_file = file_ptr->next_file;
    }

  delete file_ptr;
}

/* Handle the given event by calling the procedure associated to the
   corresponding file handler.  */

static void
handle_file_event (file_handler *file_ptr, int ready_mask)
{
  int mask;

  /* See if the desired events (mask) match the received events
     (ready_mask).  */

#ifdef HAVE_POLL
  if (use_poll)
    {
      int error_mask;

      /* With poll, the ready_mask could have any of three events set
	 to 1: POLLHUP, POLLERR, POLLNVAL.  These events cannot be
	 used in the requested event mask (events), but they can be
	 returned in the return mask (revents).  We need to check for
	 those event too, and add them to the mask which will be
	 passed to the handler.  */

      /* POLLHUP means EOF, but can be combined with POLLIN to
	 signal more data to read.  */
      error_mask = POLLHUP | POLLERR | POLLNVAL;
      mask = ready_mask & (file_ptr->mask | error_mask);

      if ((mask & (POLLERR | POLLNVAL)) != 0)
	{
	  /* Work in progress.  We may need to tell somebody
	     what kind of error we had.  */
	  if (mask & POLLERR)
	    warning (_("Error detected on fd %d"), file_ptr->fd);
	  if (mask & POLLNVAL)
	    warning (_("Invalid or non-`poll'able fd %d"),
		     file_ptr->fd);
	  file_ptr->error = 1;
	}
      else
	file_ptr->error = 0;
    }
  else
#endif /* HAVE_POLL */
    {
      if (ready_mask & GDB_EXCEPTION)
	{
	  warning (_("Exception condition detected on fd %d"),
		   file_ptr->fd);
	  file_ptr->error = 1;
	}
      else
	file_ptr->error = 0;
      mask = ready_mask & file_ptr->mask;
    }

  /* If there was a match, then call the handler.  */
  if (mask != 0)
    {
      event_loop_ui_debug_printf (file_ptr->is_ui,
				  "invoking fd file handler `%s`",
				  file_ptr->name.c_str ());
      file_ptr->proc (file_ptr->error, file_ptr->client_data);
    }
}

/* Wait for new events on the monitored file descriptors.  Run the
   event handler if the first descriptor that is detected by the poll.
   If BLOCK and if there are no events, this function will block in
   the call to poll.  Return 1 if an event was handled.  Return -1 if
   there are no file descriptors to monitor.  Return 1 if an event was
   handled, otherwise returns 0.  */

static int
gdb_wait_for_event (int block)
{
  file_handler *file_ptr;
  int num_found = 0;

  /* Make sure all output is done before getting another event.  */
  flush_streams ();

  if (gdb_notifier.num_fds == 0)
    return -1;

  if (block)
    update_wait_timeout ();

#ifdef HAVE_POLL
  if (use_poll)
    {
      int timeout;

      if (block)
	timeout = gdb_notifier.timeout_valid ? gdb_notifier.poll_timeout : -1;
      else
	timeout = 0;

      num_found = poll (gdb_notifier.poll_fds,
			(unsigned long) gdb_notifier.num_fds, timeout);

      /* Don't print anything if we get out of poll because of a
	 signal.  */
      if (num_found == -1 && errno != EINTR)
	perror_with_name (("poll"));
    }
  else
#endif /* HAVE_POLL */
    {
      struct timeval select_timeout;
      struct timeval *timeout_p;

      if (block)
	timeout_p = gdb_notifier.timeout_valid
	  ? &gdb_notifier.select_timeout : NULL;
      else
	{
	  memset (&select_timeout, 0, sizeof (select_timeout));
	  timeout_p = &select_timeout;
	}

      gdb_notifier.ready_masks[0] = gdb_notifier.check_masks[0];
      gdb_notifier.ready_masks[1] = gdb_notifier.check_masks[1];
      gdb_notifier.ready_masks[2] = gdb_notifier.check_masks[2];
      num_found = gdb_select (gdb_notifier.num_fds,
			      &gdb_notifier.ready_masks[0],
			      &gdb_notifier.ready_masks[1],
			      &gdb_notifier.ready_masks[2],
			      timeout_p);

      /* Clear the masks after an error from select.  */
      if (num_found == -1)
	{
	  FD_ZERO (&gdb_notifier.ready_masks[0]);
	  FD_ZERO (&gdb_notifier.ready_masks[1]);
	  FD_ZERO (&gdb_notifier.ready_masks[2]);

	  /* Dont print anything if we got a signal, let gdb handle
	     it.  */
	  if (errno != EINTR)
	    perror_with_name (("select"));
	}
    }

  /* Avoid looking at poll_fds[i]->revents if no event fired.  */
  if (num_found <= 0)
    return 0;

  /* Run event handlers.  We always run just one handler and go back
     to polling, in case a handler changes the notifier list.  Since
     events for sources we haven't consumed yet wake poll/select
     immediately, no event is lost.  */

  /* To level the fairness across event descriptors, we handle them in
     a round-robin-like fashion.  The number and order of descriptors
     may change between invocations, but this is good enough.  */
#ifdef HAVE_POLL
  if (use_poll)
    {
      int i;
      int mask;

      while (1)
	{
	  if (gdb_notifier.next_poll_fds_index >= gdb_notifier.num_fds)
	    gdb_notifier.next_poll_fds_index = 0;
	  i = gdb_notifier.next_poll_fds_index++;

	  gdb_assert (i < gdb_notifier.num_fds);
	  if ((gdb_notifier.poll_fds + i)->revents)
	    break;
	}

      for (file_ptr = gdb_notifier.first_file_handler;
	   file_ptr != NULL;
	   file_ptr = file_ptr->next_file)
	{
	  if (file_ptr->fd == (gdb_notifier.poll_fds + i)->fd)
	    break;
	}
      gdb_assert (file_ptr != NULL);

      mask = (gdb_notifier.poll_fds + i)->revents;
      handle_file_event (file_ptr, mask);
      return 1;
    }
  else
#endif /* HAVE_POLL */
    {
      /* See comment about even source fairness above.  */
      int mask = 0;

      do
	{
	  file_ptr = get_next_file_handler_to_handle_and_advance ();

	  if (FD_ISSET (file_ptr->fd, &gdb_notifier.ready_masks[0]))
	    mask |= GDB_READABLE;
	  if (FD_ISSET (file_ptr->fd, &gdb_notifier.ready_masks[1]))
	    mask |= GDB_WRITABLE;
	  if (FD_ISSET (file_ptr->fd, &gdb_notifier.ready_masks[2]))
	    mask |= GDB_EXCEPTION;
	}
      while (mask == 0);

      handle_file_event (file_ptr, mask);
      return 1;
    }
  return 0;
}

/* Create a timer that will expire in MS milliseconds from now.  When
   the timer is ready, PROC will be executed.  At creation, the timer
   is added to the timers queue.  This queue is kept sorted in order
   of increasing timers.  Return a handle to the timer struct.  */

int
create_timer (int ms, timer_handler_func *proc,
	      gdb_client_data client_data)
{
  using namespace std::chrono;
  struct gdb_timer *timer_ptr, *timer_index, *prev_timer;

  steady_clock::time_point time_now = steady_clock::now ();

  timer_ptr = new gdb_timer ();
  timer_ptr->when = time_now + milliseconds (ms);
  timer_ptr->proc = proc;
  timer_ptr->client_data = client_data;
  timer_list.num_timers++;
  timer_ptr->timer_id = timer_list.num_timers;

  /* Now add the timer to the timer queue, making sure it is sorted in
     increasing order of expiration.  */

  for (timer_index = timer_list.first_timer;
       timer_index != NULL;
       timer_index = timer_index->next)
    {
      if (timer_index->when > timer_ptr->when)
	break;
    }

  if (timer_index == timer_list.first_timer)
    {
      timer_ptr->next = timer_list.first_timer;
      timer_list.first_timer = timer_ptr;

    }
  else
    {
      for (prev_timer = timer_list.first_timer;
	   prev_timer->next != timer_index;
	   prev_timer = prev_timer->next)
	;

      prev_timer->next = timer_ptr;
      timer_ptr->next = timer_index;
    }

  gdb_notifier.timeout_valid = 0;
  return timer_ptr->timer_id;
}

/* There is a chance that the creator of the timer wants to get rid of
   it before it expires.  */
void
delete_timer (int id)
{
  struct gdb_timer *timer_ptr, *prev_timer = NULL;

  /* Find the entry for the given timer.  */

  for (timer_ptr = timer_list.first_timer; timer_ptr != NULL;
       timer_ptr = timer_ptr->next)
    {
      if (timer_ptr->timer_id == id)
	break;
    }

  if (timer_ptr == NULL)
    return;
  /* Get rid of the timer in the timer list.  */
  if (timer_ptr == timer_list.first_timer)
    timer_list.first_timer = timer_ptr->next;
  else
    {
      for (prev_timer = timer_list.first_timer;
	   prev_timer->next != timer_ptr;
	   prev_timer = prev_timer->next)
	;
      prev_timer->next = timer_ptr->next;
    }
  delete timer_ptr;

  gdb_notifier.timeout_valid = 0;
}

/* Convert a std::chrono duration to a struct timeval.  */

template<typename Duration>
static struct timeval
duration_cast_timeval (const Duration &d)
{
  using namespace std::chrono;
  seconds sec = duration_cast<seconds> (d);
  microseconds msec = duration_cast<microseconds> (d - sec);

  struct timeval tv;
  tv.tv_sec = sec.count ();
  tv.tv_usec = msec.count ();
  return tv;
}

/* Update the timeout for the select() or poll().  Returns true if the
   timer has already expired, false otherwise.  */

static int
update_wait_timeout (void)
{
  if (timer_list.first_timer != NULL)
    {
      using namespace std::chrono;
      steady_clock::time_point time_now = steady_clock::now ();
      struct timeval timeout;

      if (timer_list.first_timer->when < time_now)
	{
	  /* It expired already.  */
	  timeout.tv_sec = 0;
	  timeout.tv_usec = 0;
	}
      else
	{
	  steady_clock::duration d = timer_list.first_timer->when - time_now;
	  timeout = duration_cast_timeval (d);
	}

      /* Update the timeout for select/ poll.  */
#ifdef HAVE_POLL
      if (use_poll)
	gdb_notifier.poll_timeout = timeout.tv_sec * 1000;
      else
#endif /* HAVE_POLL */
	{
	  gdb_notifier.select_timeout.tv_sec = timeout.tv_sec;
	  gdb_notifier.select_timeout.tv_usec = timeout.tv_usec;
	}
      gdb_notifier.timeout_valid = 1;

      if (timer_list.first_timer->when < time_now)
	return 1;
    }
  else
    gdb_notifier.timeout_valid = 0;

  return 0;
}

/* Check whether a timer in the timers queue is ready.  If a timer is
   ready, call its handler and return.  Update the timeout for the
   select() or poll() as well.  Return 1 if an event was handled,
   otherwise returns 0.*/

static int
poll_timers (void)
{
  if (update_wait_timeout ())
    {
      struct gdb_timer *timer_ptr = timer_list.first_timer;
      timer_handler_func *proc = timer_ptr->proc;
      gdb_client_data client_data = timer_ptr->client_data;

      /* Get rid of the timer from the beginning of the list.  */
      timer_list.first_timer = timer_ptr->next;

      /* Delete the timer before calling the callback, not after, in
	 case the callback itself decides to try deleting the timer
	 too.  */
      delete timer_ptr;

      /* Call the procedure associated with that timer.  */
      (proc) (client_data);

      return 1;
    }

  return 0;
}