gdb: add debug prints in event loop

Add debug printouts about event loop-related events:

 - When a file descriptor handler gets invoked
 - When an async event/signal handler gets invoked

gdb/ChangeLog:

	* async-event.c (invoke_async_signal_handlers): Add debug
	print.
	(check_async_event_handlers): Likewise.
	* event-top.c (show_debug_event_loop): New function.
	(_initialize_event_top): Register "set debug event-loop"
	setting.

gdbserver/ChangeLog:

	* server.cc (handle_monitor_command): Handle "set
	debug-event-loop".
	(captured_main): Handle "--debug-event-loop".
	(monitor_show_help): Mention new setting.
	(gdbserver_usage): Mention new flag.

gdbsupport/ChangeLog:

	* event-loop.h (debug_event_loop): New variable declaration.
	(event_loop_debug_printf_1): New function declaration.
	(event_loop_debug_printf): New macro.
	* event-loop.cc (debug_event_loop): New variable.
	(handle_file_event): Add debug print.
	(event_loop_debug_printf_1): New function.

Change-Id: If78ed3a69179881368e7895b42940ce13b6a1a05

3 files changed, 83 insertions, 8 deletions

diff --git a/gdbsupport/ChangeLog b/gdbsupport/ChangeLog
index d5b20ec..05462e6 100644
--- a/gdbsupport/ChangeLog
+++ b/gdbsupport/ChangeLog
@@ -1,5 +1,14 @@
 2020-10-02  Simon Marchi  <simon.marchi@polymtl.ca>
 
+	* event-loop.h (debug_event_loop): New variable declaration.
+	(event_loop_debug_printf_1): New function declaration.
+	(event_loop_debug_printf): New macro.
+	* event-loop.cc (debug_event_loop): New variable.
+	(handle_file_event): Add debug print.
+	(event_loop_debug_printf_1): New function.
+
+2020-10-02  Simon Marchi  <simon.marchi@polymtl.ca>
+
 	* common-debug.cc (debug_prefixed_vprintf): Move here.
 	* common-debug.h (debug_prefixed_vprintf): Move here.
 
diff --git a/gdbsupport/event-loop.cc b/gdbsupport/event-loop.cc
index 0d78122..9494158 100644
--- a/gdbsupport/event-loop.cc
+++ b/gdbsupport/event-loop.cc
@@ -34,6 +34,10 @@
 #include "gdbsupport/gdb_sys_time.h"
 #include "gdbsupport/gdb_select.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.  */
 
@@ -64,6 +68,9 @@ struct file_handler
   /* User-friendly name of this handler.  Heap-allocated, owned by this.*/
   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;
 
@@ -164,7 +171,7 @@ timer_list;
 
 static void create_file_handler (int fd, int mask, handler_func *proc,
 				 gdb_client_data client_data,
-				 std::string &&name);
+				 std::string &&name, bool is_ui);
 static int gdb_wait_for_event (int);
 static int update_wait_timeout (void);
 static int poll_timers (void);
@@ -239,7 +246,7 @@ gdb_do_one_event (void)
 
 void
 add_file_handler (int fd, handler_func *proc, gdb_client_data client_data,
-		  std::string &&name)
+		  std::string &&name, bool is_ui)
 {
 #ifdef HAVE_POLL
   struct pollfd fds;
@@ -265,7 +272,8 @@ add_file_handler (int fd, handler_func *proc, gdb_client_data client_data,
   if (use_poll)
     {
 #ifdef HAVE_POLL
-      create_file_handler (fd, POLLIN, proc, client_data, std::move (name));
+      create_file_handler (fd, POLLIN, proc, client_data, std::move (name),
+			   is_ui);
 #else
       internal_error (__FILE__, __LINE__,
 		      _("use_poll without HAVE_POLL"));
@@ -273,7 +281,7 @@ add_file_handler (int fd, handler_func *proc, gdb_client_data client_data,
     }
   else
     create_file_handler (fd, GDB_READABLE | GDB_EXCEPTION,
-			 proc, client_data, std::move (name));
+			 proc, client_data, std::move (name), is_ui);
 }
 
 /* Helper for add_file_handler.
@@ -289,7 +297,8 @@ add_file_handler (int fd, handler_func *proc, gdb_client_data client_data,
 
 static void
 create_file_handler (int fd, int mask, handler_func * proc,
-		     gdb_client_data client_data, std::string &&name)
+		     gdb_client_data client_data, std::string &&name,
+		     bool is_ui)
 {
   file_handler *file_ptr;
 
@@ -358,6 +367,7 @@ create_file_handler (int fd, int mask, handler_func * proc,
   file_ptr->client_data = client_data;
   file_ptr->mask = mask;
   file_ptr->name = new std::string (std::move (name));
+  file_ptr->is_ui = is_ui;
 }
 
 /* Return the next file handler to handle, and advance to the next
@@ -558,7 +568,12 @@ handle_file_event (file_handler *file_ptr, int ready_mask)
 
 	  /* If there was a match, then call the handler.  */
 	  if (mask != 0)
-	    (*file_ptr->proc) (file_ptr->error, file_ptr->client_data);
+	    {
+	      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);
+	    }
 	}
     }
 }
@@ -897,3 +912,14 @@ poll_timers (void)
 
   return 0;
 }
+
+/* See event-loop.h.  */
+
+void
+event_loop_debug_printf_1 (const char *func_name, const char *fmt, ...)
+{
+  va_list args;
+  va_start (args, fmt);
+  debug_prefixed_vprintf ("event-loop", func_name, fmt, args);
+  va_end (args);
+}
diff --git a/gdbsupport/event-loop.h b/gdbsupport/event-loop.h
index d7478b0..c29d6a8 100644
--- a/gdbsupport/event-loop.h
+++ b/gdbsupport/event-loop.h
@@ -84,11 +84,13 @@ extern void delete_file_handler (int fd);
 
    FD is the file descriptor for the file/stream to be listened to.
 
-   NAME is a user-friendly name for the handler.  */
+   NAME is a user-friendly name for the handler.
+
+   If IS_UI is set, this file descriptor is used for a user interface.  */
 
 extern void add_file_handler (int fd, handler_func *proc,
 			      gdb_client_data client_data,
-			      std::string &&name);
+			      std::string &&name, bool is_ui = false);
 
 extern int create_timer (int milliseconds, 
 			 timer_handler_func *proc, 
@@ -109,4 +111,42 @@ extern int invoke_async_signal_handlers ();
 
 extern int check_async_event_handlers ();
 
+enum class debug_event_loop_kind
+{
+  OFF,
+
+  /* Print all event-loop related messages, except events from user-interface
+     event sources.  */
+  ALL_EXCEPT_UI,
+
+  /* Print all event-loop related messages.  */
+  ALL,
+};
+
+/* True if we are printing event loop debug statements.  */
+extern debug_event_loop_kind debug_event_loop;
+
+/* Print an "event loop" debug statement.  Should be used through
+   event_loop_debug_printf.  */
+void ATTRIBUTE_PRINTF (2, 3) event_loop_debug_printf_1
+  (const char *func_name, const char *fmt, ...);
+
+#define event_loop_debug_printf(fmt, ...) \
+  do \
+    { \
+      if (debug_event_loop != debug_event_loop_kind::OFF) \
+	event_loop_debug_printf_1 (__func__, fmt, ##__VA_ARGS__); \
+    } \
+  while (0)
+
+#define event_loop_ui_debug_printf(is_ui, fmt, ...) \
+  do \
+    { \
+      if (debug_event_loop == debug_event_loop_kind::ALL \
+	  || (debug_event_loop == debug_event_loop_kind::ALL_EXCEPT_UI \
+	      && !is_ui)) \
+	event_loop_debug_printf_1 (__func__, fmt, ##__VA_ARGS__); \
+    } \
+  while (0)
+
 #endif /* EVENT_LOOP_H */