DosFileLocks

This call locks and unlocks a range in an opened file.

DosFileLocks

(FileHandle, UnLockRange, LockRange)

FileHandle (HFILE) - input

File handle.
UnLockRange (PLONG) - input
Address of the structure containing the offset and length of a range to be unlocked. A doubleword of zero indicates that unlocking is not required.

FileOffset (ULONG)

The offset to the beginning of the range to be unlocked.
RangeLength (ULONG)
The length of the range to be unlocked.
LockRange (PLONG) - input
Address of the structure containing the offset and length of a range to be locked. A doubleword of zero indicates that locking is not required.

FileOffset (ULONG)

The offset to the beginning of the range to be locked.
RangeLength (ULONG)
The length of the range to be locked.
rc (USHORT) - return
Return code descriptions are:
• NO_ERROR 6
  ERROR_INVALID_HANDLE
  33
  ERROR_LOCK_VIOLATION
  36
  ERROR_SHARING_BUFFER_EXCEEDED
  Remarks

  DosFileLocks provides a mechanism that allows a process to lock a region in a file for read/write access. The time a region is locked should be short.

  Instead of denying another process read/write access to the entire file by means of access and sharing modes specified with DosOpen or DosOpen2 requests, a process attempts to lock only the the range needed for read/write access and examines the error code returned.

  A range to be locked must first be cleared of any locked subranges or overlapping ranges. The locked region can be located anywhere in the file, and locking beyond end-of-file is not considered an error.

  Once a lock is successful, read/write access by another process to the specified range is denied until the range is unlocked. If both unlocking and locking are specified by a DosFileLocks request, the unlocking operation is performed first. After unlocking is completed, locking is done.

  Duplicating the handle duplicates access to any locked regions; however, access to locked regions is not duplicated across the DosExecPgm call.

  If a file is closed (either by a DosClose request or by a process terminating) and locks are still in effect, the locks are released in no defined order.

  
  Family API Considerations

  Some options operate differently in the DOS mode than in OS/2 mode. Therefore, the following restrictions apply to DosFileLocks when coding for the DOS mode:

  o

  If Block = 1 is specified, an "invalid range lock list" or "invalid unlock list" error is returned.
  o
  NewLockIDList is not supported.

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