UBSan SEGV during destructor

[ndunsworth]

I'm trying to figure out if this is a me problem or a false positive.

During the destructor of my derived class UBSan is throwing a SEGV when the SubClass worker thread performs its cleanup and accesses the parent class impl data.

I would expect that since the DerivedClass destructor is blocked waiting for the thread to finish that the unique_ptr is still valid since the BaseClass destructor hasn't been called to free the unique_ptr.

In my debugger, lldb, when I look in the destructor of DerivedClass it shows a valid memory address for impl. However when looking at variables in cleanup_called_by_thread impl shows up as not a valid memory address.

class BaseClass {
  std::unique_ptr<ImplData> impl;
};

class DerivedClass : BaseClass {
  ~DerivedClass() {
    // blocks while the thread cleans up
    // thread has exited when this returns and no longer
    // accesses this object
    this->thread->stop();
  }

  // Called by thread during cleanup
  void cleanup_called_by_thread() {
    // this->impl shows as an invalid memory location
    ImplData* data = this->impl.get(); // SEGV
  }
}

When I print out the address of this in the cleanup func I get a totally different address then I do when i print out the address of this in the destructor.

~DerivedClass() {
    // this = 0x6356caca5470
}

DerivedClass::cleanup_called_by_thread() {
    // this = 0xa6deb54
}

Anyways I'm a noob at this but loving the different *sans, have already cleaned up a number of things since integrating them this week.