FWIW -- "This is perl, v5.8.1-RC3 built for darwin-thread-multi-2level":

After fixing the shebang line as needed, the results are mysterious.

It never seems to hang (after a dozen or so trials with and without TRACE=1). It seems to randomly alternate between two behaviors, regardless of TRACE value:

• Sometimes it exits without printing the contents of the given file; in these cases, the output is simply "TRACE=0" or "TRACE=1" followed by:

  Name "CORE::GLOBAL::warn" used only once: possible typo at ./451692.pl
  + line 11.
  t-Locking
  t-Waiting
  t-Setting
  t-Signalling
  [download]

• Other times (these seem to be in the minority), it prints the file contents before exiting; when TRACE=1, the output includes:

  Name "CORE::GLOBAL::warn" used only once: possible typo at ./451692.pl
  + line 11.
  m-locking
  m-waiting
  t-Locking
  t-Waiting
  t-Setting
  t-Signalling
  m-Copying
  m-undefing
  m-signalling
  m-processing
  [download]

Since I'm not getting any deadlocks, I'm not sure I can answer your other questions.