How to debug Segmentation Fault?

[Bottled Gin via Digitalmars-d]

Greetings

I am calling a D function from an opensource application coded in 
C/C++. My code crashes, though there is no reason for it to 
crash. Also when I call my D function from inside D, it does not 
crash. The D function does not take any arguments, nor does it 
try to access any variable declared in C/C++. So it seems to me 
that it is some memory corruption issue.

But since I am not able to reproduce the crash in standalone D 
code, I am not able to file a bug.

Can someone please guide me how I can debug this further? I have 
reduced the D code that crashes, but it crashes only when called 
from the opensource C/C++ application. The C/C++ application is 
single threaded and therefor gives full control to D function. 
And then D code runs for some time and crashes thereafter with a 
segmentation fault. I am pasting the D code below (C++ calls 
initialize function):

extern(C) void initialize() {
   import core.runtime;
   Runtime.initialize;
   frop();
}

void frop() {
   import core.thread;
   Dynamic obj = new Dynamic;
   for (size_t i; i!=200; ++i) {
     obj.rehash();
   }
   void foo() {
     for (size_t i; i!=200; ++i) {
	import std.stdio;
	writeln(i);
	obj.rehash(); // segfault happens in the second iteration of loop
	obj.proc();
       }
   }
   Thread bar = new Thread(&foo);
   bar.start();
   bar.join();
}

final class Hash {
   private Dynamic[Dynamic] _m_map;
   public void clear() {
     // only static instance of Hash is used
     // no synchronized region required -- but still
     synchronized(this) {
       _m_map = null;
     }
   }
}

class Dynamic {
   void rehash () {
     // only thread local variables no synchronized required -- 
but still
     synchronized(this) {
       static Hash hash ;
       if(hash is null) hash = new Hash;
       hash.clear();
     }
   }
   void proc () {
     // only stack variables, so no synchronized required -- but 
still
     synchronized(this) {
       char[] space;
       space.length = 5000;
     }
   }
}




//  Regards
// - Puneet