File Locking Levels
\ #define SQLITE_LOCK_NONE 0 /* xUnlock() only */\ #define SQLITE_LOCK_SHARED 1 /* xLock() or xUnlock() */\ #define SQLITE_LOCK_RESERVED 2 /* xLock() only */\ #define SQLITE_LOCK_PENDING 3 /* xLock() only */\ #define SQLITE_LOCK_EXCLUSIVE 4 /* xLock() only */\
SQLite uses one of these integer values as the second argument to calls it makes to the xLock() and xUnlock() methods of an sqlite3_io_methods object. These values are ordered from least restrictive to most restrictive.
The argument to xLock() is always SHARED or higher. The argument to xUnlock is either SHARED or NONE.