gdb/event-loop.h

   1 /* Definitions used by the GDB event loop.
   2    Copyright (C) 1999-2019 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 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 /* An event loop listens for events from multiple event sources.  When
  21    an event arrives, it is queued and processed by calling the
  22    appropriate event handler.  The event loop then continues to listen
  23    for more events.  An event loop completes when there are no event
  24    sources to listen on.  External event sources can be plugged into
  25    the loop.
  26
  27    There are 4 main components:
  28    - a list of file descriptors to be monitored, GDB_NOTIFIER.
  29    - a list of asynchronous event sources to be monitored,
  30      ASYNC_EVENT_HANDLER_LIST.
  31    - a list of events that have occurred, EVENT_QUEUE.
  32    - a list of signal handling functions, SIGHANDLER_LIST.
  33
  34    GDB_NOTIFIER keeps track of the file descriptor based event
  35    sources.  ASYNC_EVENT_HANDLER_LIST keeps track of asynchronous
  36    event sources that are signalled by some component of gdb, usually
  37    a target_ops instance.  Event sources for gdb are currently the UI
  38    and the target.  Gdb communicates with the command line user
  39    interface via the readline library and usually communicates with
  40    remote targets via a serial port.  Serial ports are represented in
  41    GDB as file descriptors and select/poll calls.  For native targets
  42    instead, the communication varies across operating system debug
  43    APIs, but usually consists of calls to ptrace and waits (via
  44    signals) or calls to poll/select (via file descriptors).  In the
  45    current gdb, the code handling events related to the target resides
  46    in wait_for_inferior for synchronous targets; or, for asynchronous
  47    capable targets, by having the target register either a target
  48    controlled file descriptor and/or an asynchronous event source in
  49    the event loop, with the fetch_inferior_event function as the event
  50    callback.  In both the synchronous and asynchronous cases, usually
  51    the target event is collected through the target_wait interface.
  52    The target is free to install other event sources in the event loop
  53    if it so requires.
  54
  55    EVENT_QUEUE keeps track of the events that have happened during the
  56    last iteration of the event loop, and need to be processed.  An
  57    event is represented by a procedure to be invoked in order to
  58    process the event.  The queue is scanned head to tail.  If the
  59    event of interest is a change of state in a file descriptor, then a
  60    call to poll or select will be made to detect it.
  61
  62    If the events generate signals, they are also queued by special
  63    functions that are invoked through traditional signal handlers.
  64    The actions to be taken is response to such events will be executed
  65    when the SIGHANDLER_LIST is scanned, the next time through the
  66    infinite loop.
  67
  68    Corollary tasks are the creation and deletion of event sources.  */
  69
  70 typedef void *gdb_client_data;
  71 struct async_signal_handler;
  72 struct async_event_handler;
  73 typedef void (handler_func) (int, gdb_client_data);
  74 typedef void (sig_handler_func) (gdb_client_data);
  75 typedef void (async_event_handler_func) (gdb_client_data);
  76 typedef void (timer_handler_func) (gdb_client_data);
  77
  78 /* Exported functions from event-loop.c */
  79
  80 extern void start_event_loop (void);
  81 extern int gdb_do_one_event (void);
  82 extern void delete_file_handler (int fd);
  83 extern void add_file_handler (int fd, handler_func *proc,
  84                               gdb_client_data client_data);
  85 extern struct async_signal_handler *
  86   create_async_signal_handler (sig_handler_func *proc,
  87                                gdb_client_data client_data);
  88 extern void delete_async_signal_handler (struct async_signal_handler **);
  89 extern int create_timer (int milliseconds,
  90                          timer_handler_func *proc,
  91                          gdb_client_data client_data);
  92 extern void delete_timer (int id);
  93
  94 /* Call the handler from HANDLER the next time through the event
  95    loop.  */
  96 extern void mark_async_signal_handler (struct async_signal_handler *handler);
  97
  98 /* Returns true if HANDLER is marked ready.  */
  99
 100 extern int
 101   async_signal_handler_is_marked (struct async_signal_handler *handler);
 102
 103 /* Mark HANDLER as NOT ready.  */
 104
 105 extern void clear_async_signal_handler (struct async_signal_handler *handler);
 106
 107 /* Create and register an asynchronous event source in the event loop,
 108    and set PROC as its callback.  CLIENT_DATA is passed as argument to
 109    PROC upon its invocation.  Returns a pointer to an opaque structure
 110    used to mark as ready and to later delete this event source from
 111    the event loop.  */
 112 extern struct async_event_handler *
 113   create_async_event_handler (async_event_handler_func *proc,
 114                               gdb_client_data client_data);
 115
 116 /* Remove the event source pointed by HANDLER_PTR created by
 117    CREATE_ASYNC_EVENT_HANDLER from the event loop, and release it.  */
 118 extern void
 119   delete_async_event_handler (struct async_event_handler **handler_ptr);
 120
 121 /* Call the handler from HANDLER the next time through the event
 122    loop.  */
 123 extern void mark_async_event_handler (struct async_event_handler *handler);
 124
 125 /* Mark the handler (ASYNC_HANDLER_PTR) as NOT ready.  */
 126
 127 extern void clear_async_event_handler (struct async_event_handler *handler);
 128
 129 extern void initialize_async_signal_handlers (void);