Re: gtkmm 3.0 and libsigc++

[Chris Vine <chris cvine freeserve co uk>]

On Thu, 29 Jul 2010 01:45:04 +0100
Chris Vine <chris cvine freeserve co uk> wrote:
[snip]
> But, as I say, it is the thread safety of remote trackable objects
> which seems to me to be the more pressing point.

The gory details of my conclusions when I last looked at this are
coming back to me, and as you have probably by now concluded it is not
as simple as that.

When the destructor of a remote object deriving from trackable nulls
any slots referring to its methods, those slots will be nulled in the
thread in which the destructor executes, which may not be the thread
which "owns" a particular signal object which might emit on the slot.
If and when that other thread does emit, the slot may (as far as its
memory visibility is concerned) be in an inconsistent state.  The
problem would be even worse if the remote trackable not only nulls the
slots, but also removes them from the signal object (I cannot now
recall whether it does that or not, but I suspect that it does).

So in practice it is probably impossible to make trackable meaningfully
thread safe without also making signals and connection objects thread
safe.

Chris