gdbsupport/event-loop.h

   1 /* Definitions used by the GDB event loop.
   2    Copyright (C) 1999-2021 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 #ifndef EVENT_LOOP_H
  21 #define EVENT_LOOP_H
  22
  23 /* An event loop listens for events from multiple event sources.  When
  24    an event arrives, it is queued and processed by calling the
  25    appropriate event handler.  The event loop then continues to listen
  26    for more events.  An event loop completes when there are no event
  27    sources to listen on.  External event sources can be plugged into
  28    the loop.
  29
  30    There are 4 main components:
  31    - a list of file descriptors to be monitored, GDB_NOTIFIER.
  32    - a list of asynchronous event sources to be monitored,
  33      ASYNC_EVENT_HANDLER_LIST.
  34    - a list of events that have occurred, EVENT_QUEUE.
  35    - a list of signal handling functions, SIGHANDLER_LIST.
  36
  37    GDB_NOTIFIER keeps track of the file descriptor based event
  38    sources.  ASYNC_EVENT_HANDLER_LIST keeps track of asynchronous
  39    event sources that are signalled by some component of gdb, usually
  40    a target_ops instance.  Event sources for gdb are currently the UI
  41    and the target.  Gdb communicates with the command line user
  42    interface via the readline library and usually communicates with
  43    remote targets via a serial port.  Serial ports are represented in
  44    GDB as file descriptors and select/poll calls.  For native targets
  45    instead, the communication varies across operating system debug
  46    APIs, but usually consists of calls to ptrace and waits (via
  47    signals) or calls to poll/select (via file descriptors).  In the
  48    current gdb, the code handling events related to the target resides
  49    in wait_for_inferior for synchronous targets; or, for asynchronous
  50    capable targets, by having the target register either a target
  51    controlled file descriptor and/or an asynchronous event source in
  52    the event loop, with the fetch_inferior_event function as the event
  53    callback.  In both the synchronous and asynchronous cases, usually
  54    the target event is collected through the target_wait interface.
  55    The target is free to install other event sources in the event loop
  56    if it so requires.
  57
  58    EVENT_QUEUE keeps track of the events that have happened during the
  59    last iteration of the event loop, and need to be processed.  An
  60    event is represented by a procedure to be invoked in order to
  61    process the event.  The queue is scanned head to tail.  If the
  62    event of interest is a change of state in a file descriptor, then a
  63    call to poll or select will be made to detect it.
  64
  65    If the events generate signals, they are also queued by special
  66    functions that are invoked through traditional signal handlers.
  67    The actions to be taken is response to such events will be executed
  68    when the SIGHANDLER_LIST is scanned, the next time through the
  69    infinite loop.
  70
  71    Corollary tasks are the creation and deletion of event sources.  */
  72
  73 typedef void *gdb_client_data;
  74 typedef void (handler_func) (int, gdb_client_data);
  75 typedef void (timer_handler_func) (gdb_client_data);
  76
  77 /* Exported functions from event-loop.c */
  78
  79 extern int gdb_do_one_event (void);
  80 extern void delete_file_handler (int fd);
  81
  82 /* Add a file handler/descriptor to the list of descriptors we are
  83    interested in.
  84
  85    FD is the file descriptor for the file/stream to be listened to.
  86
  87    NAME is a user-friendly name for the handler.
  88
  89    If IS_UI is set, this file descriptor is used for a user interface.  */
  90
  91 extern void add_file_handler (int fd, handler_func *proc,
  92                               gdb_client_data client_data,
  93                               std::string &&name, bool is_ui = false);
  94
  95 extern int create_timer (int milliseconds,
  96                          timer_handler_func *proc,
  97                          gdb_client_data client_data);
  98 extern void delete_timer (int id);
  99
 100 /* Must be defined by client.  */
 101
 102 extern void handle_event_loop_exception (const gdb_exception &);
 103
 104 /* Must be defined by client.  Returns true if any signal handler was
 105    ready.  */
 106
 107 extern int invoke_async_signal_handlers ();
 108
 109 /* Must be defined by client.  Returns true if any event handler was
 110    ready.  */
 111
 112 extern int check_async_event_handlers ();
 113
 114 enum class debug_event_loop_kind
 115 {
 116   OFF,
 117
 118   /* Print all event-loop related messages, except events from user-interface
 119      event sources.  */
 120   ALL_EXCEPT_UI,
 121
 122   /* Print all event-loop related messages.  */
 123   ALL,
 124 };
 125
 126 /* True if we are printing event loop debug statements.  */
 127 extern debug_event_loop_kind debug_event_loop;
 128
 129 /* Print an "event loop" debug statement.  */
 130
 131 #define event_loop_debug_printf(fmt, ...) \
 132   debug_prefixed_printf_cond (debug_event_loop != debug_event_loop_kind::OFF, \
 133                               "event-loop", fmt, ##__VA_ARGS__)
 134
 135 /* Print an "event loop" debug statement that is know to come from a UI-related
 136    event (e.g. calling the event handler for the fd of the CLI).  */
 137
 138 #define event_loop_ui_debug_printf(is_ui, fmt, ...) \
 139   do \
 140     { \
 141       if (debug_event_loop == debug_event_loop_kind::ALL \
 142           || (debug_event_loop == debug_event_loop_kind::ALL_EXCEPT_UI \
 143               && !is_ui)) \
 144         debug_prefixed_printf ("event-loop", __func__, fmt, ##__VA_ARGS__); \
 145     } \
 146   while (0)
 147
 148 #endif /* EVENT_LOOP_H */