SQLITE_LOCK_NONE, SQLITE_LOCK_SHARED, SQLITE_LOCK_RESERVED, SQLITE_LOCK_PENDING, SQLITE_LOCK_EXCLUSIVE

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 lest restrictive to most restrictive. The argument to xLock() is ... 

 ... Only a single RESERVED lock may be active at one time, though multiple SHARED locks can coexist with a single RESERVED lock. RESERVED differs from PENDING in that new SHARED locks can be acquired while there is a RESERVED lock ... 

 ... SQLITE_ABORT, SQLITE_BUSY, SQLITE_LOCKED, SQLITE_NOMEM, SQLITE_READONLY, SQLITE_INTERRUPT ... 

Many SQLite functions return an integer result code from the set shown here in order to indicate success or failure. New error codes may be added in future versions of SQLite. See also: extended result code definitions See also lists ... 

2.2. Table Level Locking When two or more connections use a shared-cache, locks are used to serialize concurrent access attempts on a per-table basis. Tables support two types of locks, "read-locks" and "write-locks". Locks are granted to connections - at any ... 

 ... Before reading, a read (shared) lock must be obtained. A connection releases all held table locks when it concludes its transaction. If a connection cannot obtain a required lock, then the call to sqlite3_step() returns SQLITE_LOCKED. Although it is less ... 

struct sqlite3_io_methods

 ... Potential uses for xFileControl() might be functions to enable blocking locks with timeouts, to change the locking strategy (for example to use dot-file locks), to inquire about the status of a lock, or to break stale locks. The SQLite ... 

2.3. Locking Matrix Access is coordinated in WAL mode using both the legacy DELETE-mode locks controlled by the xLock and xUnlock methods of the sqlite3_io_methods object and the WAL locks controlled by the xShmLock method of the sqlite3_io_methods object. Conceptually, there is ... 

sqlite3_busy_handler()

 ... Consider a scenario where one process is holding a read lock that it is trying to promote to a reserved lock and a second process is holding a reserved lock that it is trying to promote to an exclusive lock ... 

sqlite3_unlock_notify()

When running in shared-cache mode, a database operation may fail with an SQLITE_LOCKED error if the required locks on the shared-cache or individual tables within the shared-cache cannot be obtained. See SQLite Shared-Cache Mode for a ... 

sqlite3_db_cacheflush()

 ... If this function needs to obtain extra database locks before dirty pages can be flushed to disk, it does so. If those locks cannot be obtained immediately and there is a busy-handler callback configured, it is invoked in the ...