Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!ucbvax!decwrl!hplabs!hp-pcd!hplsla!jima
From: jima@hplsla.HP.COM (Jim Adcock)
Newsgroups: comp.lang.c++
Subject: Re: GC (was Re: Eiffel vs. C++ (vs Smalltalk))
Message-ID: <6590170@hplsla.HP.COM>
Date: 24 Jun 89 00:27:53 GMT
References: <14739@duke.cs.duke.edu>
Organization: HP Lake Stevens, WA
Lines: 77

The following simple program makes random length trees -- and fools Boehm's
GC.  I seem to remember something about this in his README file.  Maybe one
had better bone up on his algorithm before getting too deep in this.

(change either 2 to a 3 (25% chance verses 50% chance) in randomlinks and
 the GC works fine.  Program is not "publication quality.")

-----------
#include <stdio.h>
#include "gc++.h"

extern "C"
{
  int rand();
};

void* ::operator new(long sz)
{
  return gc_malloc((sz < 8) ? 8 : sz);
}

void ::operator delete(void *p)
{
  if (p) gc_free(p);
}

class link
{
public:
  link* head;
  link* tail;
  link() {head = 0; tail = 0;}
  void randomlinks();
};

long sum;

void link::randomlinks()
{
  if (!(rand() & 2))
  {
    head = new link;
    head->randomlinks();
    sum += sizeof(link);
  }

  if (!(rand() & 2))
  {
    tail = new link;
    tail->randomlinks();
    sum += sizeof(link);
  }
}
  
main()
{
  link * p[4096];
  initialize_allocator();

  long cntinc = 4096;
  int n, q;

  while (1)
  {
      q = 0x0ff & rand();
      p[q] = new link;
      sum += sizeof(link);
      (p[q])->randomlinks();

      if (sum > cntinc)
      {
	  cntinc <<= 1;
	  printf("\n *** total 'lost' so far: %d ***\n\n",sum);
	  if (sum > 4000000) exit(0);
      }
  }
}