gdb/tui: use wrefresh if output is not surpressed
Recent work in the TUI has improved GDB's use of the curses
wnoutrefresh and doupdate mechanism, which improves performance by
batching together updates and then doing a single set of writes to the
screen when doupdate is finally called.
The tui_batch_rendering type is a RAII class which, in its destructor,
calls doupdate to send the batched updates to the screen.
However, if there is no tui_batch_rendering active on the call stack
then any wnoutrefresh calls will remain batched but undisplayed until
the next time doupdate happens to be called.
This problem can be seen in PR gdb/32623. When an inferior is started
the 'Starting program' message is not immediately displayed to the
user.
The 'Starting program' message originates from run_command_1 in
infcmd.c, the message is sent to the current_uiout, which will be the
TUI ui_out. After the message is sent, ui_out::flush() is called,
here's the backtrace when that happens:
#0 tui_file::flush (this=0x36e4ab0) at ../../src/gdb/tui/tui-file.c:42
#1 0x0000000001004f4b in pager_file::flush (this=0x36d35f0) at ../../src/gdb/utils.c:1531
#2 0x0000000001004f71 in gdb_flush (stream=0x36d35f0) at ../../src/gdb/utils.c:1539
#3 0x00000000006975ab in cli_ui_out::do_flush (this=0x35a50b0) at ../../src/gdb/cli-out.c:250
#4 0x00000000009fd1f9 in ui_out::flush (this=0x35a50b0) at ../../src/gdb/ui-out.h:263
#5 0x00000000009f56ad in run_command_1 (args=0x0, from_tty=1, run_how=RUN_NORMAL) at ../../src/gdb/infcmd.c:449
#6 0x00000000009f599a in run_command (args=0x0, from_tty=1) at ../../src/gdb/infcmd.c:511
And if we check out tui_file::flush (tui-file.c) we can see that this
just calls tui_win_info::refresh_window(), which in turn, just uses
wnoutrefresh to batch any pending output.
The problem is that, in the above backtrace, there is no
tui_batch_rendering active, and so there will be no doupdate call to
flush the output to the screen.
We could add a tui_batch_rendering into tui_file::flush. And
tui_file::write. And tui_file::puts .....
... but that all seems a bit unnecessary. Instead, I propose that
tui_win_info::refresh_window() should be changed. If suppress_output
is true (i.e. a tui_batch_rendering is active) then we should continue
to call wnoutrefresh(). But if suppress_output is false, meaning that
no tui_batch_rendering is in place, then we should call wrefresh(),
which immediately writes the output to the screen.
Testing but PR gdb/32623 was a little involved. We need to 'run' the
inferior and check for the 'Starting program' message. But DejaGNUU
can only check for the message once it knows the message should have
appeared. But, as the bug is that output is not displayed, we don't
have any output hints that the inferior is started yet...
In the end, I have the inferior create a file in the test's output
directory. Now DejaGNU can send the 'run' command, and wait for the
file to appear. Once that happens, we know that the 'Starting
program' message should have appeared.
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=32623
Approved-By: Tom Tromey <tom@tromey.com>
3 files changed
