Re: Announce - Thread safety annotations no longer supported in GCC

[Delesley Hutchins <delesley at google dot com>]

> Why wouldn't it be constructive?
>
> Even if it's impractical for gcc to change to the degree needed to fit
> your particular project (especially in the short term), hearing the
> details of how gcc's representations fell short, and how others may
> have done things better, seems useful.

My main concern is to avoid turning this into a "clang vs. gcc"
debate.  The two compilers make different trade-offs, so it is hardly
surprising that one is better than the other for a particular use
case.  That does not mean that one is better than the other overall.
But since it seems that there is significant interest, I have written
down some of the technical problems that we ran into when working with
gcc.   Description and accompanying source code are enclosed.

  -DeLesley

Attachment: gcc-problem-description.txt
Description: Text document

class Mutex {
public:
  void Lock();
  void Unlock();
};

class MyClass {
public:
  virtual void myMethod();
  MyClass();
  ~MyClass();
};

// (1) Inaccurate CFG
void foo1(Mutex* mu, bool c) {
  mu->Lock();
  if (c) {
    MyClass mc;
    if (c) {
      mu->Unlock();
      return;
    }
    // extra join point here to call ~MyClass()
  }
  mu->Unlock();
  return;
};

// (2) Inaccurate type information
void foo2(void* p) {
  ((MyClass*) p)->myMethod();
}

// (3) Problem with optimizations
class DummyMutex {
public:
  void Lock()   { }
  void Unlock() { }
};

void foo3(DummyMutex* dmu1, DummyMutex* dmu2) {
  dmu1->Lock();
  dmu2->Lock();
  dmu2->Unlock();
  dmu1->Unlock();
}