Re: [RFA] PR python/13598 - add before_prompt event

[Pedro Alves <palves at redhat dot com>]

On 07/23/2016 06:00 AM, Tom Tromey wrote:
>>>>>> "Matt" == Matt Rice <ratmice@gmail.com> writes:
> 
> Matt> In particular it's just a nice time to take a snapshot of some
> Matt> otherwise obtainable property from gdb right before control is handed
> Matt> back to the user.
> 
> Yes, this is exactly why I added this.
> 
> My original motivation was to get a notification when the selected frame
> changed.  However, this happens a lot, sometimes temporarily.  And, I
> wasn't interested in temporary frame changes -- just "final" changes,
> such as just after a command has completed and just before the prompt is
> displayed... which led to this approach.
> 
> Right now my GUI uses this event to react appropriately when the user
> types "up" or "down".

The TUI uses this approach too nowadays.

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commit 0986c744dfecb8177de90020646090e9ed23cfe7
Author:     Patrick Palka <patrick@parcs.ath.cx>
AuthorDate: Tue Jun 30 13:56:49 2015 -0400

    Replace TUI's select_frame hook (PR tui/13378)
    
    The select_frame hook is used by TUI to update TUI's frame and register
    information following changes to the selected frame.  The problem with
    this hook is that it gets called after every single frame change, even
    if the frame change is only temporary or internal.  This is the primary
    cause of flickering and slowdown when running the inferior under TUI
    with conditional breakpoints set.  Internal GDB events are the source of
    many calls to select_frame and these internal events are triggered
    frequently, especially when a few conditional breakpoints are set.
    
    This patch removes the select_frame hook altogether and instead makes
    the frame and register information get updated in two key places (using
    observers): after an inferior stops, and right before displaying a
    prompt.  The latter hook covers the case when frame information must be
    updated following a call to "up", "down" or "frame", and the former
    covers the case when frame and register information must be updated
    after a call to "continue", "step", etc. or after the inferior stops in
    async execution mode.  Together these hooks should cover all the cases
    when frame information ought to be refreshed (and when the relevant
    windows ought to be subsequently updated).
[...]
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Thanks,
Pedro Alves