[lldb-dev] Too many ModuleSP references

[Zachary Turner via lldb-dev]

No comments on this specifically, but +1 to reducing shared_ptr usage in
general. We use way too many, and often it feels like shared_ptr is used as
a way to avoid having to think about ownership, which leads to more
problems than it solves imo
On Tue, Feb 21, 2017 at 9:03 AM Pavel Labath via lldb-dev <
lldb-dev at lists.llvm.org> wrote:

> Hello all,
>
> I've been debugging the newly added TestStepOverBreakpoint.py, which
> has been failing on windows, for a very prosaic reason: after the test
> completes, we are unable to run "make clean" because lldb still holds
> the file open.
>
> After some debugging, I've found that this happens because the test
> case stores the SBBreakpoint object in a member variable of the python
> test case class. The breakpoint class ends up transitively holding a
> reference to the main executable module, which prevents the module
> from being garbage-collected when the target is destroyed.
>
> For reference, the full ownership chain is something like:
> StepOverBreakpointTestCase(python) => SBBreakpoint => Breakpoint =>
> BreakpointLocation => LLVMUserExpression => IRExecutionUnit =>
> SymbolContext => Module.
>
> To get the test working, we need to break this chain somewhere. A
> couple of places I see are:
> - BreakpointLocation: Remove the compiled expression reference when
> the target is destroyed (AFAICS, it is used as a cache to avoid
> recomputing the expression every time. It can be theoretically
> recomputed if needed, but that shouldn't be necessary as the target is
> destroyed anyway)
>
> - SBBreakpoint: make SBBreakpoint hold a weak_ptr to the Breakpoint
> object. When the target is destroyed, the SBBreakpoint object becomes
> invalid (One doesn't cannot do anything useful with the breakpoint
> once the target has been deleted anyway).
>
> - StepOverBreakpointTestCase: Have the test not store the breakpoints
> in the test case object. Basically, declare that this is not a bug,
> and it's the users responsibility to clean up necessary objects.
>
> Any thoughts on what is the appropriate solution here?
>
> cheers,
> pavel
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