Lock

Restricts read/write access to a file or portion of a file

Syntax
	Lock #filenum, record
	Lock #filenum, start To end

Parameters
	filenum
		The file number used to KeyPgOpenOpen the file.
	record
		The record (KeyPgRandomRandom files) to lock.
	start
		The first byte position (KeyPgBinaryBinary files) to lock from.
	end
		The last byte position (KeyPgBinaryBinary files) to lock to.

Description
	Lock temporarily restricts access by other threads or programs to a 
	file, or portion of a file, usually to allow safe writing to it.

	After modifying the data, an KeyPgUnlockUnlock with the same parameters as the Lock 
	should be issued.

	Note: This command does not always work, neither as documented nor as 
	expected. It appears to be broken at the moment.

Example
	'' e.g. locking a file, reading 100 bytes, and unlocking it. 
	'' To run, make sure there exists a file called 'file.ext' 
	'' in the current directory that is at least 100 bytes.

	Dim array(1 To 100) As Integer
	Dim f As Integer, i As Integer
	f = FreeFile
	Open "file.ext" For Binary As #f
	Lock #f, 1 To 100
	For i = 1 To 100
	   Get #f, i, array(i)
	Next
	Unlock #f, 1 To 100
	Close #f

Differences from QB
	* Currently, FB cannot implicitly lock the entire file
	* In KeyPgRandomRandom mode, FB cannot lock a range of records

See also
	* KeyPgOpenOpen
	* KeyPgUnlockUnlock
	* KeyPgScreenlockScreenLock

