Look more closely at how you're obtaining a lock:

  1. You are opening a lock to a semaphore file (lock.tmp).
  2. Once that lock is obtained you are opening an output file (somefile$_.tmp).
  3. You unlock/close your semaphore file.
  4. You write to somefile$_.tmp
  5. You close somefile$_.tmp.
  6. You copy from your tmp file to a new file.

Steps 4, 5, and 6 are unprotected.

You should not be releasing your semaphore file lock until after you're done writing to somefile$_.tmp, and in fact, probably not even until after the copy operation. And probably shouldn't be using LOCK_UN as a matter of habit (simply closing a filehandle will terminate the lock, and explicitly unlocking before closing can create a race condition, though not in this usage.)

You may already know about this set of slides from Mark Jason Dominus, but just in case: File Locking Tricks and Traps.


Dave

In reply to Re: Strange IO + concurrency issue by davido
in thread [SOLVED] Strange IO + concurrency issue by vsespb

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