Move event-loop.[ch] to gdbsupport/

This moves event-loop.[ch] to gdbsupport/ and updates the uses in gdb.

gdb/ChangeLog
2020-04-13  Tom Tromey  <tom@tromey.com>

	* run-on-main-thread.c: Update include.
	* unittests/main-thread-selftests.c: Update include.
	* tui/tui-win.c: Update include.
	* tui/tui-io.c: Update include.
	* tui/tui-interp.c: Update include.
	* tui/tui-hooks.c: Update include.
	* top.h: Update include.
	* top.c: Update include.
	* ser-base.c: Update include.
	* remote.c: Update include.
	* remote-notif.c: Update include.
	* remote-fileio.c: Update include.
	* record-full.c: Update include.
	* record-btrace.c: Update include.
	* python/python.c: Update include.
	* posix-hdep.c: Update include.
	* mingw-hdep.c: Update include.
	* mi/mi-main.c: Update include.
	* mi/mi-interp.c: Update include.
	* main.c: Update include.
	* linux-nat.c: Update include.
	* interps.c: Update include.
	* infrun.c: Update include.
	* inf-loop.c: Update include.
	* event-top.c: Update include.
	* event-loop.c: Move to ../gdbsupport/.
	* event-loop.h: Move to ../gdbsupport/.
	* async-event.h: Update include.
	* Makefile.in (COMMON_SFILES, HFILES_NO_SRCDIR): Update.

gdbsupport/ChangeLog
2020-04-13  Tom Tromey  <tom@tromey.com>

	* event-loop.h: Move from ../gdb/.
	* event-loop.cc: Move from ../gdb/.

5 files changed, 1009 insertions, 10 deletions

diff --git a/gdbsupport/ChangeLog b/gdbsupport/ChangeLog
index a065a9a..1e64022 100644
--- a/gdbsupport/ChangeLog
+++ b/gdbsupport/ChangeLog
@@ -1,5 +1,10 @@
 2020-04-13  Tom Tromey  <tom@tromey.com>
 
+	* event-loop.h: Move from ../gdb/.
+	* event-loop.cc: Move from ../gdb/.
+
+2020-04-13  Tom Tromey  <tom@tromey.com>
+
 	* errors.h (flush_streams): Declare.
 
 2020-04-13  Tom Tromey  <tom@tromey.com>
diff --git a/gdbsupport/Makefile.am b/gdbsupport/Makefile.am
index ee78a89..e95ee5d 100644
--- a/gdbsupport/Makefile.am
+++ b/gdbsupport/Makefile.am
@@ -46,6 +46,7 @@ libgdbsupport_a_SOURCES = \
     common-utils.cc \
     environ.cc \
     errors.cc \
+    event-loop.cc \
     fileio.cc \
     filestuff.cc \
     format.cc \
diff --git a/gdbsupport/Makefile.in b/gdbsupport/Makefile.in
index 7ed2e6f..5051ab3 100644
--- a/gdbsupport/Makefile.in
+++ b/gdbsupport/Makefile.in
@@ -149,16 +149,16 @@ am_libgdbsupport_a_OBJECTS = agent.$(OBJEXT) btrace-common.$(OBJEXT) \
 	buffer.$(OBJEXT) cleanups.$(OBJEXT) common-debug.$(OBJEXT) \
 	common-exceptions.$(OBJEXT) common-inferior.$(OBJEXT) \
 	common-regcache.$(OBJEXT) common-utils.$(OBJEXT) \
-	environ.$(OBJEXT) errors.$(OBJEXT) fileio.$(OBJEXT) \
-	filestuff.$(OBJEXT) format.$(OBJEXT) gdb-dlfcn.$(OBJEXT) \
-	gdb_tilde_expand.$(OBJEXT) gdb_wait.$(OBJEXT) \
-	gdb_vecs.$(OBJEXT) job-control.$(OBJEXT) netstuff.$(OBJEXT) \
-	new-op.$(OBJEXT) pathstuff.$(OBJEXT) print-utils.$(OBJEXT) \
-	ptid.$(OBJEXT) rsp-low.$(OBJEXT) run-time-clock.$(OBJEXT) \
-	safe-strerror.$(OBJEXT) scoped_mmap.$(OBJEXT) \
-	signals.$(OBJEXT) signals-state-save-restore.$(OBJEXT) \
-	tdesc.$(OBJEXT) thread-pool.$(OBJEXT) xml-utils.$(OBJEXT) \
-	$(am__objects_1)
+	environ.$(OBJEXT) errors.$(OBJEXT) event-loop.$(OBJEXT) \
+	fileio.$(OBJEXT) filestuff.$(OBJEXT) format.$(OBJEXT) \
+	gdb-dlfcn.$(OBJEXT) gdb_tilde_expand.$(OBJEXT) \
+	gdb_wait.$(OBJEXT) gdb_vecs.$(OBJEXT) job-control.$(OBJEXT) \
+	netstuff.$(OBJEXT) new-op.$(OBJEXT) pathstuff.$(OBJEXT) \
+	print-utils.$(OBJEXT) ptid.$(OBJEXT) rsp-low.$(OBJEXT) \
+	run-time-clock.$(OBJEXT) safe-strerror.$(OBJEXT) \
+	scoped_mmap.$(OBJEXT) signals.$(OBJEXT) \
+	signals-state-save-restore.$(OBJEXT) tdesc.$(OBJEXT) \
+	thread-pool.$(OBJEXT) xml-utils.$(OBJEXT) $(am__objects_1)
 libgdbsupport_a_OBJECTS = $(am_libgdbsupport_a_OBJECTS)
 AM_V_P = $(am__v_P_@AM_V@)
 am__v_P_ = $(am__v_P_@AM_DEFAULT_V@)
@@ -368,6 +368,7 @@ libgdbsupport_a_SOURCES = \
     common-utils.cc \
     environ.cc \
     errors.cc \
+    event-loop.cc \
     fileio.cc \
     filestuff.cc \
     format.cc \
@@ -471,6 +472,7 @@ distclean-compile:
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/common-utils.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/environ.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/errors.Po@am__quote@
+@AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/event-loop.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/fileio.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/filestuff.Po@am__quote@
 @AMDEP_TRUE@@am__include@ @am__quote@./$(DEPDIR)/format.Po@am__quote@
diff --git a/gdbsupport/event-loop.cc b/gdbsupport/event-loop.cc
new file mode 100644
index 0000000..f7ccc4e
--- /dev/null
+++ b/gdbsupport/event-loop.cc
@@ -0,0 +1,889 @@
+/* Event loop machinery for GDB, the GNU debugger.
+   Copyright (C) 1999-2020 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"
+
+/* 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.  */
+
+typedef struct file_handler
+  {
+    int fd;			/* File descriptor.  */
+    int mask;			/* Events we want to monitor: POLLIN, etc.  */
+    int ready_mask;		/* Events that have been seen since
+				   the last time.  */
+    handler_func *proc;		/* Procedure to call when fd is ready.  */
+    gdb_client_data client_data;	/* Argument to pass to proc.  */
+    int error;			/* Was an error detected on this fd?  */
+    struct file_handler *next_file;	/* Next registered file descriptor.  */
+  }
+file_handler;
+
+/* 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.  */
+
+/* As of 1999-04-30 only the input file descriptor is registered with the
+   event loop.  */
+
+/* Do we use poll or select ? */
+#ifdef HAVE_POLL
+#define USE_POLL 1
+#else
+#define USE_POLL 0
+#endif /* HAVE_POLL */
+
+static unsigned char use_poll = USE_POLL;
+
+#ifdef USE_WIN32API
+#include <windows.h>
+#include <io.h>
+#endif
+
+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);
+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 for something to happen (via gdb_wait_for_event), then process
+   it.  Returns >0 if something was done otherwise returns <0 (this
+   can happen if there are no event sources to wait for).  */
+
+int
+gdb_do_one_event (void)
+{
+  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 (__FILE__, __LINE__,
+			  "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;
+    }
+
+  /* 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 (gdb_wait_for_event (1) < 0)
+    return -1;
+
+  /* If gdb_wait_for_event has returned 1, it means that one event has
+     been handled.  We break out of the loop.  */
+  return 1;
+}
+
+
+
+/* Wrapper function for create_file_handler, so that the caller
+   doesn't have to know implementation details about the use of poll
+   vs. select.  */
+void
+add_file_handler (int fd, handler_func * proc, gdb_client_data client_data)
+{
+#ifdef HAVE_POLL
+  struct pollfd fds;
+#endif
+
+  if (use_poll)
+    {
+#ifdef HAVE_POLL
+      /* 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 = 0;
+#else
+      internal_error (__FILE__, __LINE__,
+		      _("use_poll without HAVE_POLL"));
+#endif /* HAVE_POLL */
+    }
+  if (use_poll)
+    {
+#ifdef HAVE_POLL
+      create_file_handler (fd, POLLIN, proc, client_data);
+#else
+      internal_error (__FILE__, __LINE__,
+		      _("use_poll without HAVE_POLL"));
+#endif
+    }
+  else
+    create_file_handler (fd, GDB_READABLE | GDB_EXCEPTION, 
+			 proc, client_data);
+}
+
+/* Add a file handler/descriptor to the list of descriptors we are
+   interested in.
+
+   FD is the file descriptor for the file/stream to be listened to.
+
+   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)
+{
+  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 = XNEW (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;
+
+      if (use_poll)
+	{
+#ifdef HAVE_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
+	  internal_error (__FILE__, __LINE__,
+			  _("use_poll without HAVE_POLL"));
+#endif /* HAVE_POLL */
+	}
+      else
+	{
+	  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;
+}
+
+/* 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;
+#ifdef HAVE_POLL
+  int j;
+  struct pollfd *new_poll_fds;
+#endif
+
+  /* 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;
+
+  if (use_poll)
+    {
+#ifdef HAVE_POLL
+      /* 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
+      internal_error (__FILE__, __LINE__,
+		      _("use_poll without HAVE_POLL"));
+#endif /* HAVE_POLL */
+    }
+  else
+    {
+      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;
+    }
+  xfree (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;
+#ifdef HAVE_POLL
+  int error_mask;
+#endif
+
+    {
+	{
+	  /* 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.  */
+
+	  /* See if the desired events (mask) match the received
+	     events (ready_mask).  */
+
+	  if (use_poll)
+	    {
+#ifdef HAVE_POLL
+	      /* 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
+	      internal_error (__FILE__, __LINE__,
+			      _("use_poll without HAVE_POLL"));
+#endif /* HAVE_POLL */
+	    }
+	  else
+	    {
+	      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)
+	    (*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 ();
+
+  if (use_poll)
+    {
+#ifdef HAVE_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
+      internal_error (__FILE__, __LINE__,
+		      _("use_poll without HAVE_POLL"));
+#endif /* HAVE_POLL */
+    }
+  else
+    {
+      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.  */
+  if (use_poll)
+    {
+#ifdef HAVE_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
+      internal_error (__FILE__, __LINE__,
+		      _("use_poll without HAVE_POLL"));
+#endif /* HAVE_POLL */
+    }
+  else
+    {
+      /* 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.  */
+      if (use_poll)
+	{
+#ifdef HAVE_POLL
+	  gdb_notifier.poll_timeout = timeout.tv_sec * 1000;
+#else
+	  internal_error (__FILE__, __LINE__,
+			  _("use_poll without HAVE_POLL"));
+#endif /* HAVE_POLL */
+	}
+      else
+	{
+	  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;
+}
diff --git a/gdbsupport/event-loop.h b/gdbsupport/event-loop.h
new file mode 100644
index 0000000..2eaaa0c
--- /dev/null
+++ b/gdbsupport/event-loop.h
@@ -0,0 +1,102 @@
+/* Definitions used by the GDB event loop.
+   Copyright (C) 1999-2020 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/>.  */
+
+#ifndef EVENT_LOOP_H
+#define EVENT_LOOP_H
+
+/* An event loop listens for events from multiple event sources.  When
+   an event arrives, it is queued and processed by calling the
+   appropriate event handler.  The event loop then continues to listen
+   for more events.  An event loop completes when there are no event
+   sources to listen on.  External event sources can be plugged into
+   the loop.
+
+   There are 4 main components:
+   - a list of file descriptors to be monitored, GDB_NOTIFIER.
+   - a list of asynchronous event sources to be monitored,
+     ASYNC_EVENT_HANDLER_LIST.
+   - a list of events that have occurred, EVENT_QUEUE.
+   - a list of signal handling functions, SIGHANDLER_LIST.
+
+   GDB_NOTIFIER keeps track of the file descriptor based event
+   sources.  ASYNC_EVENT_HANDLER_LIST keeps track of asynchronous
+   event sources that are signalled by some component of gdb, usually
+   a target_ops instance.  Event sources for gdb are currently the UI
+   and the target.  Gdb communicates with the command line user
+   interface via the readline library and usually communicates with
+   remote targets via a serial port.  Serial ports are represented in
+   GDB as file descriptors and select/poll calls.  For native targets
+   instead, the communication varies across operating system debug
+   APIs, but usually consists of calls to ptrace and waits (via
+   signals) or calls to poll/select (via file descriptors).  In the
+   current gdb, the code handling events related to the target resides
+   in wait_for_inferior for synchronous targets; or, for asynchronous
+   capable targets, by having the target register either a target
+   controlled file descriptor and/or an asynchronous event source in
+   the event loop, with the fetch_inferior_event function as the event
+   callback.  In both the synchronous and asynchronous cases, usually
+   the target event is collected through the target_wait interface.
+   The target is free to install other event sources in the event loop
+   if it so requires.
+
+   EVENT_QUEUE keeps track of the events that have happened during the
+   last iteration of the event loop, and need to be processed.  An
+   event is represented by a procedure to be invoked in order to
+   process the event.  The queue is scanned head to tail.  If the
+   event of interest is a change of state in a file descriptor, then a
+   call to poll or select will be made to detect it.
+
+   If the events generate signals, they are also queued by special
+   functions that are invoked through traditional signal handlers.
+   The actions to be taken is response to such events will be executed
+   when the SIGHANDLER_LIST is scanned, the next time through the
+   infinite loop.
+
+   Corollary tasks are the creation and deletion of event sources.  */
+
+typedef void *gdb_client_data;
+typedef void (handler_func) (int, gdb_client_data);
+typedef void (timer_handler_func) (gdb_client_data);
+
+/* Exported functions from event-loop.c */
+
+extern int gdb_do_one_event (void);
+extern void delete_file_handler (int fd);
+extern void add_file_handler (int fd, handler_func *proc, 
+			      gdb_client_data client_data);
+extern int create_timer (int milliseconds, 
+			 timer_handler_func *proc, 
+			 gdb_client_data client_data);
+extern void delete_timer (int id);
+
+/* Must be defined by client.  */
+
+extern void handle_event_loop_exception (const gdb_exception &);
+
+/* Must be defined by client.  Returns true if any signal handler was
+   ready.  */
+
+extern int invoke_async_signal_handlers ();
+
+/* Must be defined by client.  Returns true if any event handler was
+   ready.  */
+
+extern int check_async_event_handlers ();
+
+#endif /* EVENT_LOOP_H */