Files
binutils-gdb/gdb/ui-out.h
Simon Marchi 44c04ee9bf Decouple user selection from internal selection
I am sending this as an RFC because it's far from complete and
definitive, but I'd like to gather some comments and opinions before
going further in this direction.

The goal of this patch is to decouple the notion of the user-selected
inferior/thread/frame from GDB's internally selected
inferior/thread/frame.

Currently, for example, the inferior_ptid variable has two jobs:

 - it's the user-selected thread: it's changed by the "thread" command.
   Other commands (continue, backtrace, etc) apply to this thread.
 - it's the internally-selected thread: it defines the thread GDB is
   currently "working" on.  For example, implementations of
   to_xfer_partial will refer to it to know from which thread to
   read/write memory.

Because of this dual usage, if we want to do some operations on a thread
other than the currently selected one, we have to save the current
inferior/thread/frame and restore them when we're done.  Failing to do
so would result in an unexpected selection switch for the user.

To improve this, Pedro suggested in [1] to decouple the two concepts.  This
is essentially what this patch is trying to do.

A new "user_selection" object is introduced, which contains the selected
inferior/thread/frame from the point of view of the user.  Before every
command, we "apply" this selection to the core of GDB to make sure the
internal selection matches the user selection.

There is a single user selection for the whole GDB (named "global
user-selection"), but as was mentioned in the linked thread, it opens
the door to having different selections for different UIs.  This means
that each UI would have its own user-selection object, which would be
applied to the core prior to executing commands from this UI.

The global user-selection object only gets modified when we really
intend to change it.  It can be because of the thread / -thread-select /
up / down / frame / inferior commands, a breakpoint hit in all-stop, an
inferior exit, etc.

The problem that initially prompted this effort is that the "--thread"
flag of MI commands changes the user-selected thread under the user's
feet.  My initial attempt to fix it was to restore the selection after
the MI command execution.  However, some cases are hard to get right.
For example:

  (thread 1 is currently selected)
  -interpreter-exec --thread 2 console "thread 3"

Restoring the selected thread to thread 1 after the MI command execution
wrongfully cancels the switch to thread 3.  So it's hard to determine
when we should or shouldn't restore.   With the current patch, it works
naturally: the --thread flag doesn't touch the user-selected thread,
only the internal one.  The "thread 3" command updates the user
selection.

Another difficulty is to send the right notifications to MI when the
user selection changes.  That means to not miss any, but not send too
many either.  Getting it somewhat right lead to ugly hacks (see the
command_notifies_uscc_observer function) and even then it's not perfect
(see the kfails in user-selected-context-sync.exp test).  With the
proposed method, it's easy to know when the user-selection changes and
send notifications.

With this patch, there are probably a few usage of
make_cleanup_restore_current_thread that are not needed anymore, if they
are only used to restore the user selection.  I kept removing them for a
later time though.

In the current state, there are a few minor regressions in the testsuite
(especially some follow-fork stuff I'm not sure how to handle), but the
vast majority of the previously passing tests still pass.

Comments are welcome!

Thanks,

Simon

[1] https://sourceware.org/ml/gdb-patches/2016-08/msg00031.html
2017-02-23 17:25:30 -05:00

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/* Output generating routines for GDB.
Copyright (C) 1999-2017 Free Software Foundation, Inc.
Contributed by Cygnus Solutions.
Written by Fernando Nasser for Cygnus.
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 UI_OUT_H
#define UI_OUT_H 1
#include <vector>
#include "common/enum-flags.h"
class ui_out_level;
class ui_out_table;
struct ui_file;
/* the current ui_out */
/* FIXME: This should not be a global but something passed down from main.c
or top.c. */
extern struct ui_out **current_ui_current_uiout_ptr (void);
#define current_uiout (*current_ui_current_uiout_ptr ())
/* alignment enum */
enum ui_align
{
ui_left = -1,
ui_center,
ui_right,
ui_noalign
};
/* flags enum */
enum ui_out_flag
{
ui_source_list = (1 << 0),
};
DEF_ENUM_FLAGS_TYPE (ui_out_flag, ui_out_flags);
/* Prototypes for ui-out API. */
/* A result is a recursive data structure consisting of lists and
tuples. */
enum ui_out_type
{
ui_out_type_tuple,
ui_out_type_list
};
extern struct cleanup *make_cleanup_ui_out_table_begin_end (struct ui_out *ui_out,
int nr_cols,
int nr_rows,
const char *tblid);
/* Compatibility wrappers. */
extern struct cleanup *make_cleanup_ui_out_list_begin_end (struct ui_out *uiout,
const char *id);
extern struct cleanup *make_cleanup_ui_out_tuple_begin_end (struct ui_out *uiout,
const char *id);
class ui_out
{
public:
explicit ui_out (ui_out_flags flags = 0);
virtual ~ui_out ();
void push_level (ui_out_type type);
void pop_level (ui_out_type type);
/* A table can be considered a special tuple/list combination with the
implied structure: ``table = { hdr = { header, ... } , body = [ {
field, ... }, ... ] }''. If NR_ROWS is negative then there is at
least one row. */
void table_begin (int nr_cols, int nr_rows, const std::string &tblid);
void table_header (int width, ui_align align, const std::string &col_name,
const std::string &col_hdr);
void table_body ();
void table_end ();
void begin (ui_out_type type, const char *id);
void end (ui_out_type type);
void field_int (const char *fldname, int value);
void field_fmt_int (int width, ui_align align, const char *fldname,
int value);
void field_core_addr (const char *fldname, struct gdbarch *gdbarch,
CORE_ADDR address);
void field_string (const char *fldname, const char *string);
void field_stream (const char *fldname, string_file &stream);
void field_skip (const char *fldname);
void field_fmt (const char *fldname, const char *format, ...)
ATTRIBUTE_PRINTF (3, 4);
void spaces (int numspaces);
void text (const char *string);
void message (const char *format, ...) ATTRIBUTE_PRINTF (2, 3);
void wrap_hint (const char *identstring);
void flush ();
/* Redirect the output of a ui_out object temporarily. */
void redirect (ui_file *outstream);
ui_out_flags test_flags (ui_out_flags mask);
/* HACK: Code in GDB is currently checking to see the type of ui_out
builder when determining which output to produce. This function is
a hack to encapsulate that test. Once GDB manages to separate the
CLI/MI from the core of GDB the problem should just go away .... */
bool is_mi_like_p ();
bool query_table_field (int colno, int *width, int *alignment,
const char **col_name);
protected:
virtual void do_table_begin (int nbrofcols, int nr_rows, const char *tblid)
= 0;
virtual void do_table_body () = 0;
virtual void do_table_end () = 0;
virtual void do_table_header (int width, ui_align align,
const std::string &col_name,
const std::string &col_hdr) = 0;
virtual void do_begin (ui_out_type type, const char *id) = 0;
virtual void do_end (ui_out_type type) = 0;
virtual void do_field_int (int fldno, int width, ui_align align,
const char *fldname, int value) = 0;
virtual void do_field_skip (int fldno, int width, ui_align align,
const char *fldname) = 0;
virtual void do_field_string (int fldno, int width, ui_align align,
const char *fldname, const char *string) = 0;
virtual void do_field_fmt (int fldno, int width, ui_align align,
const char *fldname, const char *format,
va_list args)
ATTRIBUTE_PRINTF (6,0) = 0;
virtual void do_spaces (int numspaces) = 0;
virtual void do_text (const char *string) = 0;
virtual void do_message (const char *format, va_list args)
ATTRIBUTE_PRINTF (2,0) = 0;
virtual void do_wrap_hint (const char *identstring) = 0;
virtual void do_flush () = 0;
virtual void do_redirect (struct ui_file *outstream) = 0;
/* Set as not MI-like by default. It is overridden in subclasses if
necessary. */
virtual bool do_is_mi_like_p ()
{ return false; }
private:
ui_out_flags m_flags;
/* Vector to store and track the ui-out levels. */
std::vector<std::unique_ptr<ui_out_level>> m_levels;
/* A table, if any. At present only a single table is supported. */
std::unique_ptr<ui_out_table> m_table_up;
void verify_field (int *fldno, int *width, ui_align *align);
int level () const;
ui_out_level *current_level () const;
};
/* This is similar to make_cleanup_ui_out_tuple_begin_end and
make_cleanup_ui_out_list_begin_end, but written as an RAII template
class. It takes the ui_out_type as a template parameter. Normally
this is used via the typedefs ui_out_emit_tuple and
ui_out_emit_list. */
template<ui_out_type Type>
class ui_out_emit_type
{
public:
ui_out_emit_type (struct ui_out *uiout, const char *id)
: m_uiout (uiout)
{
uiout->begin (Type, id);
}
~ui_out_emit_type ()
{
m_uiout->end (Type);
}
ui_out_emit_type (const ui_out_emit_type<Type> &) = delete;
ui_out_emit_type<Type> &operator= (const ui_out_emit_type<Type> &)
= delete;
private:
struct ui_out *m_uiout;
};
typedef ui_out_emit_type<ui_out_type_tuple> ui_out_emit_tuple;
typedef ui_out_emit_type<ui_out_type_list> ui_out_emit_list;
template <class T>
class scoped_restore_suppress_output
{
public:
scoped_restore_suppress_output (T* obj)
: m_obj (obj),
m_val (m_obj->suppress_output ())
{}
~scoped_restore_suppress_output ()
{
m_obj->suppress_output (m_val);
}
private:
T* m_obj;
bool m_val;
};
#endif /* UI_OUT_H */