open(MFILE, ">>$completeadd") || die "file open1 failed: $!\n";
  close(MFILE);
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What is the point of this?

Can you shed light on why the file contents "disappear"?

While the code you display isn't the way I would do it, I don't think there's anything wrong in the code you show. Of course, you don't show us writedata or release_lock - it could be that the problem lies there.

Abigail