In each memory location store the number of incoming pointers

Free the block if the counter is zero

Jargon File:

One day a student came to Moon and said, "I understand how to
make a better garbage collector.  We must keep a reference count
of the pointers to each cons."

Moon patiently told the student the following story:

      "One day a student came to Moon and said, `I understand how
      to make a better garbage collector...

What is the block has further pointers? - deallocation may take long time

• decrementing counts when the r is reused again
• ensures a bounded amount of work for each operation

Two problems of reference counting

• cost of field assignments = ?
• for which classes of graphs it works?

Data-flow analysis for avoiding reference count updates of local variables