gdb/event-loop.h

   1 /* Definitions used by the GDB event loop.
   2    Copyright (C) 1999, 2000, 2007, 2008, 2009, 2010, 2011
   3    Free Software Foundation, Inc.
   4    Written by Elena Zannoni <ezannoni@cygnus.com> of Cygnus Solutions.
   5
   6    This file is part of GDB.
   7
   8    This program is free software; you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 3 of the License, or
  11    (at your option) any later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
  20
  21 /* An event loop listens for events from multiple event sources.  When
  22    an event arrives, it is queued and processed by calling the
  23    appropriate event handler.  The event loop then continues to listen
  24    for more events.  An event loop completes when there are no event
  25    sources to listen on.  External event sources can be plugged into
  26    the loop.
  27
  28    There are 4 main components:
  29    - a list of file descriptors to be monitored, GDB_NOTIFIER.
  30    - a list of asynchronous event sources to be monitored,
  31      ASYNC_EVENT_HANDLER_LIST.
  32    - a list of events that have occurred, EVENT_QUEUE.
  33    - a list of signal handling functions, SIGHANDLER_LIST.
  34
  35    GDB_NOTIFIER keeps track of the file descriptor based event
  36    sources.  ASYNC_EVENT_HANDLER_LIST keeps track of asynchronous
  37    event sources that are signalled by some component of gdb, usually
  38    a target_ops instance.  Event sources for gdb are currently the UI
  39    and the target.  Gdb communicates with the command line user
  40    interface via the readline library and usually communicates with
  41    remote targets via a serial port.  Serial ports are represented in
  42    GDB as file descriptors and select/poll calls.  For native targets
  43    instead, the communication varies across operating system debug
  44    APIs, but usually consists of calls to ptrace and waits (via
  45    signals) or calls to poll/select (via file descriptors).  In the
  46    current gdb, the code handling events related to the target resides
  47    in wait_for_inferior for synchronous targets; or, for asynchronous
  48    capable targets, by having the target register either a target
  49    controlled file descriptor and/or an asynchronous event source in
  50    the event loop, with the fetch_inferior_event function as the event
  51    callback.  In both the synchronous and asynchronous cases, usually
  52    the target event is collected through the target_wait interface.
  53    The target is free to install other event sources in the event loop
  54    if it so requires.
  55
  56    EVENT_QUEUE keeps track of the events that have happened during the
  57    last iteration of the event loop, and need to be processed.  An
  58    event is represented by a procedure to be invoked in order to
  59    process the event.  The queue is scanned head to tail.  If the
  60    event of interest is a change of state in a file descriptor, then a
  61    call to poll or select will be made to detect it.
  62
  63    If the events generate signals, they are also queued by special
  64    functions that are invoked through traditional signal handlers.
  65    The actions to be taken is response to such events will be executed
  66    when the SIGHANDLER_LIST is scanned, the next time through the
  67    infinite loop.
  68
  69    Corollary tasks are the creation and deletion of event sources.  */
  70
  71 typedef void *gdb_client_data;
  72 struct async_signal_handler;
  73 struct async_event_handler;
  74 typedef void (handler_func) (int, gdb_client_data);
  75 typedef void (sig_handler_func) (gdb_client_data);
  76 typedef void (async_event_handler_func) (gdb_client_data);
  77 typedef void (timer_handler_func) (gdb_client_data);
  78
  79 /* Where to add an event onto the event queue, by queue_event.  */
  80 typedef enum
  81   {
  82     /* Add at tail of queue.  It will be processed in first in first
  83        out order.  */
  84     TAIL,
  85     /* Add at head of queue.  It will be processed in last in first
  86        out order.  */
  87     HEAD
  88   }
  89 queue_position;
  90
  91 /* Exported functions from event-loop.c */
  92
  93 extern void start_event_loop (void);
  94 extern int gdb_do_one_event (void *data);
  95 extern void delete_file_handler (int fd);
  96 extern void add_file_handler (int fd, handler_func *proc,
  97                               gdb_client_data client_data);
  98 extern struct async_signal_handler *
  99   create_async_signal_handler (sig_handler_func *proc,
 100                                gdb_client_data client_data);
 101 extern void delete_async_signal_handler (struct async_signal_handler **);
 102 extern int create_timer (int milliseconds,
 103                          timer_handler_func *proc,
 104                          gdb_client_data client_data);
 105 extern void delete_timer (int id);
 106
 107 /* Call the handler from HANDLER immediately.  This function
 108    runs signal handlers when returning to the event loop would be too
 109    slow.  Do not call this directly; use gdb_call_async_signal_handler,
 110    below, with IMMEDIATE_P == 1.  */
 111 void call_async_signal_handler (struct async_signal_handler *handler);
 112
 113 /* Call the handler from HANDLER the next time through the event loop.
 114    Do not call this directly; use gdb_call_async_signal_handler,
 115    below, with IMMEDIATE_P == 0.  */
 116 void mark_async_signal_handler (struct async_signal_handler *handler);
 117
 118 /* Wrapper for the body of signal handlers.  Call this function from
 119    any SIGINT handler which needs to access GDB data structures or
 120    escape via longjmp.  If IMMEDIATE_P is set, this triggers either
 121    immediately (for POSIX platforms), or from gdb_select (for
 122    MinGW).  If IMMEDIATE_P is clear, the handler will run the next
 123    time we return to the event loop and any current select calls
 124    will be interrupted.  */
 125
 126 void gdb_call_async_signal_handler (struct async_signal_handler *handler,
 127                                     int immediate_p);
 128
 129 /* Create and register an asynchronous event source in the event loop,
 130    and set PROC as its callback.  CLIENT_DATA is passed as argument to
 131    PROC upon its invocation.  Returns a pointer to an opaque structure
 132    used to mark as ready and to later delete this event source from
 133    the event loop.  */
 134 extern struct async_event_handler *
 135   create_async_event_handler (async_event_handler_func *proc,
 136                               gdb_client_data client_data);
 137
 138 /* Remove the event source pointed by HANDLER_PTR created by
 139    CREATE_ASYNC_EVENT_HANDLER from the event loop, and release it.  */
 140 extern void
 141   delete_async_event_handler (struct async_event_handler **handler_ptr);
 142
 143 /* Call the handler from HANDLER the next time through the event
 144    loop.  */
 145 extern void mark_async_event_handler (struct async_event_handler *handler);