Say there's a bug that causes a program to hang, but it's hard to reproduce.  It might be worth inserting assertions in code that traverses a linked structure to check that the length is less than some (very large) maximum:

  int chk_count = 0;
  while (p = p->next) {
    twiddle(p);
    chk_count++;
    ASSERT(chk_count < 1000000);  // way too large
  }

If the assertion fails, then you know that somehow the program's got a cycle in the list, or something else has gone wrong.  Hopefully the assertion failure produced a core dump, and you can grovel through that to find the problem.

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CategoryDebugging CategoryAssertions