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Cygwin: FIFO: fix hit_eof

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According to Posix, a FIFO open for reading is at EOF if it is empty
and there are no writers open.

The only way to test this is to poll the fifo_client_handlers as in
raw_read and select.cc:peek_fifo.  The current hit_eof instead relies
on the value of nconnected, which can be out of date.  On the one
hand, it doesn't take into account writers that were connected but
have since closed.  On the other hand, it doesn't take into account
writers that are in the process of opening but haven't yet connected.

Fix this by introducing a maybe_eof method that tentatively assumes
EOF if there are no connected writers after polling.  Then check for
writers currently opening (via a new 'writer_opening' event), and wait
for the fifo_reader_thread to record any new connection that was made
while we were polling.

To handle the needs of peek_fifo, replace the get_fc_handle method
by a get_fc_handler method, and add a fifo_client_handler::get_state
method.

Remove the is_connected method, which was used only in peek_fifo and
is no longer needed.

Remove the nconnected data member, which was used only for the flawed
hit_eof.

Add some comments about events to fhandler.h.
This commit is contained in:
Ken Brown
2020-04-26 09:38:46 -04:00
parent 13c65c43c2
commit 301454f132
3 changed files with 98 additions and 49 deletions
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44
winsup/cygwin/select.cc
View File

@@ -866,31 +866,45 @@ peek_fifo (select_record *s, bool from_select)
goto out;
}
if (fh->hit_eof ())
{
select_printf ("read: %s, saw EOF", fh->get_name ());
gotone = s->read_ready = true;
if (s->except_selected)
gotone += s->except_ready = true;
goto out;
}
fh->fifo_client_lock ();
int nconnected = 0;
for (int i = 0; i < fh->get_nhandlers (); i++)
if (fh->is_connected (i))
if (fh->get_fc_handler (i).get_state () >= fc_connected)
{
int n = pipe_data_available (s->fd, fh, fh->get_fc_handle (i),
false);
if (n > 0)
nconnected++;
switch (fh->get_fc_handler (i).pipe_state ())
{
select_printf ("read: %s, ready for read: avail %d, client %d",
fh->get_name (), n, i);
case FILE_PIPE_CONNECTED_STATE:
fh->get_fc_handler (i).get_state () = fc_connected;
break;
case FILE_PIPE_DISCONNECTED_STATE:
fh->get_fc_handler (i).get_state () = fc_disconnected;
nconnected--;
break;
case FILE_PIPE_CLOSING_STATE:
fh->get_fc_handler (i).get_state () = fc_closing;
break;
case FILE_PIPE_INPUT_AVAILABLE_STATE:
fh->get_fc_handler (i).get_state () = fc_input_avail;
select_printf ("read: %s, ready for read", fh->get_name ());
fh->fifo_client_unlock ();
gotone += s->read_ready = true;
goto out;
default:
fh->get_fc_handler (i).get_state () = fc_error;
nconnected--;
break;
}
}
fh->maybe_eof (!nconnected);
fh->fifo_client_unlock ();
if (fh->maybe_eof () && fh->hit_eof ())
{
select_printf ("read: %s, saw EOF", fh->get_name ());
gotone += s->read_ready = true;
if (s->except_selected)
gotone += s->except_ready = true;
}
}
out:
if (s->write_selected)