LockFileEx
The LockFileEx
function locks a byte range within an open file for shared or exclusive access.
BOOL LockFileEx(
|
HANDLE hFile, |
// handle of file
to lock |
|
DWORD dwFlags, |
// functional
behavior modification flags |
|
DWORD dwReserved, |
// reserved, must
be set to zero |
|
DWORD nNumberOfBytesToLockLow, |
// low-order 32
bits of length to lock |
|
DWORD nNumberOfBytesToLockHigh, |
// high-order 32
bits of length to lock |
|
LPOVERLAPPED lpOverlapped |
// addr. of
structure with lock region start offset
|
|
); |
|
Parameters
hFile
Identifies an
open handle to a file that is to have a range of bytes locked for shared or
exclusive access. The handle must have been created with either GENERIC_READ or
GENERIC_WRITE access to the file.
dwFlags
Specifies
flags that modify the behavior of this function. This parameter may be one or
more of the following values:
|
Value |
Meaning |
|
LOCKFILE_FAIL_IMMEDIATELY |
If this
value is specified, the function returns immediately if it is unable to
acquire the requested lock. Otherwise, it waits. |
|
LOCKFILE_EXCLUSIVE_LOCK |
If this
value is specified, the function requests an exclusive lock. Otherwise, it
requests a shared lock. |
dwReserved
Reserved
parameter; must be set to zero.
nNumberOfBytesToLockLow
Specifies the
low-order 32 bits of the length of the byte range to lock.
nNumberOfBytesToLockHigh
Specifies the
high-order 32 bits of the length of the byte range to lock.
lpOverlapped
Points to an OVERLAPPED structure that the
function uses with the locking request. This structure, which is required,
contains the file offset of the beginning of the lock range.
Return Values
If the
function succeeds, the return value is nonzero.
If the
function fails, the return value is zero or NULL. To get extended error
information, call GetLastError.
Remarks
Locking a
region of a file is used to acquire shared or exclusive access to the specified
region of the file. File locks are not inherited by a new process during
process creation.
Locking a
portion of a file for exclusive access denies all other processes both read and
write access to the specified region of the file. Locking a region that goes
beyond the current end-of-file position is not an error.
Locking a
portion of a file for shared access denies all processes write access to the
specified region of the file, including the process that first locks the
region. All processes can read the locked region.
If an
exclusive lock is requested for a range of a file that already has a shared or
exclusive lock, this call waits until the lock is granted, unless the
LOCKFILE_FAIL_IMMEDIATELY flag is specified.
Locks may not
overlap an existing locked region of the file.
See Also