[PATCH] Speed up "gdb -tui" output

Eli Zaretskii
2015-01-06T16:12:37Z

In the TUI mode, we call wrefresh after outputting every single
character. Since fputs_* functions go through fputc_*, i.e. break
their writes into single characters as well, and tui_putc makes a
1-character string out of every character and passes it to tui_puts,
every time GDB wants to display more than a few characters, the I/O
becomes very slow.

I guess TUI relies on the curses library or the underlying stdio to do
the buffering, but the Windows build of ncurses doesn't buffer and
doesn't use stdio.

The simple patch below speeds up GDB output in TUI mode several orders
of magnitude, especially on Windows XP (but there's a very prominent
speedup on Windows 7 as well).

Any objections (ChangeLog entry will be added, of course)?

*** gdb/tui/tui-io.c~1 2015-01-03 11:12:52.187500000 +0200
--- gdb/tui/tui-io.c 2015-01-06 17:59:55.098500000 +0200
*************** tui_puts (const char *string)
*** 201,209 ****
TUI_CMD_WIN->detail.command_info.start_line
= TUI_CMD_WIN->detail.command_info.cur_line;

! /* We could defer the following. */
! wrefresh (w);
! fflush (stdout);
}

/* Readline callback.
--- 201,211 ----
TUI_CMD_WIN->detail.command_info.start_line
= TUI_CMD_WIN->detail.command_info.cur_line;

! if (c == '\n')
! {
! wrefresh (w);
! fflush (stdout);
! }
}

/* Readline callback.