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   ◄Summary►  ◄Notes►  ◄Back►
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▀ This function is useful for file and record synchronization in a multi-
  tasking environment or network. Access to the file as a whole is control-
  led by the attribute and file-sharing parameters passed in open or create
  calls, and by the file's attributes, which are stored in its directory
  entry.
 
▀ The beginning location in the file to be locked or unlocked is supplied
  as a positive double-precision integer, which is a byte offset into the
  file. The length of the region to be locked or unlocked is similarly sup-
  plied as a positive double-precision integer.
 
▀ For every call to lock a region of a file, there must be a subsequent un-
  lock call with exactly the same file offset and length.
 
▀ Locking beyond the current end of file is not an error.
 
▀ If a process terminates without releasing active locks on a file, the re-
  sult is undefined. Therefore, programs using this function should install
  their own Int 23H and Int 24H handlers so the processes cannot be termin-
  ated unexpectedly.
 
▀ Programs that are loaded with the EXEC call (Int 21H Function 4BH) inherit
  the handles of their parent but not any active locks.
 
▀ Duplicate handles created with Int 21H Function 45H, or handles redirected
  to the file with Int 21H Function 46H, are allowed access to locked regions
  within the same process.
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