[PATCH] Use std::vector in event-loop.cc

[PATCH] Use std::vector in event-loop.cc

[Tom Tromey]

In my occasional and continuing campaign against realloc, this patch
changes event-loop.cc to use std::vector to keep track of pollfd
objects.  Regression tested on x86-64 Fedora 38.
---
 gdbsupport/event-loop.cc | 57 +++++++++++++---------------------------
 1 file changed, 18 insertions(+), 39 deletions(-)

diff --git a/gdbsupport/event-loop.cc b/gdbsupport/event-loop.cc
index b18a9fdaac0..4f7ad36d8d6 100644
--- a/gdbsupport/event-loop.cc
+++ b/gdbsupport/event-loop.cc
@@ -112,8 +112,8 @@ static struct
     file_handler *next_file_handler;
 
 #ifdef HAVE_POLL
-    /* Ptr to array of pollfd structures.  */
-    struct pollfd *poll_fds;
+    /* Descriptors to poll.  */
+    std::vector<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
@@ -336,17 +336,11 @@ create_file_handler (int fd, int mask, handler_func * proc,
       if (use_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;
+	  struct pollfd new_fd;
+	  new_fd.fd = fd;
+	  new_fd.events = mask;
+	  new_fd.revents = 0;
+	  gdb_notifier.poll_fds.push_back (new_fd);
 	}
       else
 #endif /* HAVE_POLL */
@@ -426,28 +420,13 @@ delete_file_handler (int fd)
 #ifdef HAVE_POLL
   if (use_poll)
     {
-      int j;
-      struct pollfd *new_poll_fds;
-
-      /* 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;
+      auto iter = std::remove_if (gdb_notifier.poll_fds.begin (),
+				  gdb_notifier.poll_fds.end (),
+				  [=] (const pollfd &item)
+				  {
+				    return item.fd == fd;
+				  });
+      gdb_notifier.poll_fds.erase (iter, gdb_notifier.poll_fds.end());
       gdb_notifier.num_fds--;
     }
   else
@@ -605,7 +584,7 @@ gdb_wait_for_event (int block)
       else
 	timeout = 0;
 
-      num_found = poll (gdb_notifier.poll_fds,
+      num_found = poll (gdb_notifier.poll_fds.data (),
 			(unsigned long) gdb_notifier.num_fds, timeout);
 
       /* Don't print anything if we get out of poll because of a
@@ -676,7 +655,7 @@ gdb_wait_for_event (int block)
 	  i = gdb_notifier.next_poll_fds_index++;
 
 	  gdb_assert (i < gdb_notifier.num_fds);
-	  if ((gdb_notifier.poll_fds + i)->revents)
+	  if (gdb_notifier.poll_fds[i].revents)
 	    break;
 	}
 
@@ -684,12 +663,12 @@ gdb_wait_for_event (int block)
 	   file_ptr != NULL;
 	   file_ptr = file_ptr->next_file)
 	{
-	  if (file_ptr->fd == (gdb_notifier.poll_fds + i)->fd)
+	  if (file_ptr->fd == gdb_notifier.poll_fds[i].fd)
 	    break;
 	}
       gdb_assert (file_ptr != NULL);
 
-      mask = (gdb_notifier.poll_fds + i)->revents;
+      mask = gdb_notifier.poll_fds[i].revents;
       handle_file_event (file_ptr, mask);
       return 1;
     }
-- 
2.43.0

Re: [PATCH] Use std::vector in event-loop.cc

[Simon Marchi]

On 2024-04-06 14:39, Tom Tromey wrote:
> In my occasional and continuing campaign against realloc, this patch
> changes event-loop.cc to use std::vector to keep track of pollfd
> objects.  Regression tested on x86-64 Fedora 38.

This LGTM.

Approved-By: Simon Marchi <simon.marchi@efficios.com>

I almost commented to say that the `num_fds` could be removed, that you
could use the vector size instead.  But then I saw that num_fds is also
used as the max fd number when using select.  I then saw that I had an
old draft patch that would remove the select code in event-loop.cc and
elsewhere.  The problem is that I don't remember the rationale for
starting such a patch.  Probably that all platforms we support have
something better than select for event handling, but I don't know for
sure.  But it would certainly help clean things up if we could remove
the select support.

Simon

Re: [PATCH] Use std::vector in event-loop.cc

[John Baldwin]

On 4/6/24 2:39 PM, Tom Tromey wrote:
> In my occasional and continuing campaign against realloc, this patch
> changes event-loop.cc to use std::vector to keep track of pollfd
> objects.  Regression tested on x86-64 Fedora 38.

A noble quest surely

Approved-By: John Baldwin <jhb@FreeBSD.org>

-- 
John Baldwin