Hi @all,

how to fix an SIGSEGV in invariant._d_invariant(Object)?

Maybe i should give some context:

I am learning D and started hacking the dlangide(https://github.com/buggins/dlangide), and normally finding the cause of an segmentation fault isn't that hard. But this time it is somehow different because gdb prints something about a function "_d_invariant" and not directly giving the stack trace.

I guess the segmentation fault happens somewhere in the druntime (https://github.com/D-Programming-Language/druntime/blob/master/src/rt/invariant.d).

I am wondering if am searching i the right direction. Should i try to debug the runtime somehow or better search in the application code to find the reason?


This is the output from gdb crashdump:

Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
Core was generated by `bin/dlangide'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x0000000000cca5de in invariant._d_invariant(Object) ()
[Current thread is 1 (Thread 0x7fd86bf965c0 (LWP 3665))]
(gdb) up
#1  0x0000000000c2f092 in dlangui.widgets.lists.StringListAdapter.itemCount() const (
    this=0x7fd85bc03d00) at ../.dub/packages/dlangui-0.7.32/src/dlangui/widgets/lists.d:306
306	    @property override int itemCount() const {
(gdb) up
#2  0x0000000000c2fefe in dlangui.widgets.lists.ListWidget.itemCount() (this=0x7fd85c3af400)
    at ../.dub/packages/dlangui-0.7.32/src/dlangui/widgets/lists.d:513
513	            return _adapter.itemCount;

On Wednesday, 6 January 2016 at 21:50:23 UTC, Keywan Ghadami wrote:
> how to fix an SIGSEGV in invariant._d_invariant(Object)?

That means you are calling a method on a null object.

Your object might be at the bottom of the stack trace listing. Check your code for a declared class that you forgot to use `new` on, that's usually the cause with new users (in D, you must explicitly new all classes you create.)

On Wednesday, 6 January 2016 at 21:58:51 UTC, Adam D. Ruppe wrote:
> On Wednesday, 6 January 2016 at 21:50:23 UTC, Keywan Ghadami wrote:
>> how to fix an SIGSEGV in invariant._d_invariant(Object)?
>
> That means you are calling a method on a null object.
>
> Your object might be at the bottom of the stack trace listing. Check your code for a declared class that you forgot to use `new` on, that's usually the cause with new users (in D, you must explicitly new all classes you create.)

Hi thank you, i am glad to read that i can focus on the applicatin code, and that stacktrace. If i read that stack trace correctly the segfault happens while accessing a struct within the method of a class instance.

This instance is the object "_adapter" that can not be null please see the following code from line 512.

    @property int itemCount() {
        if (_adapter !is null)
            return _adapter.itemCount;
        return 0;
    }

could it be that this instance was deallocated from anonther thread, or can it really be be that the object was never created. if so than i do not understand why i do not get a SIGSEGV for the initial method call.