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int sqlite3_initialize(void); int sqlite3_shutdown(void); int sqlite3_os_init(void); int sqlite3_os_end(void);
The sqlite3_initialize() routine initializes the SQLite library. The sqlite3_shutdown() routine deallocates any resources that were allocated by sqlite3_initialize(). These routines are designed to aid in process initialization and shutdown on embedded systems. Workstation applications using SQLite normally do not need to invoke either of these routines.
A call to sqlite3_initialize() is an "effective" call if it is the first time sqlite3_initialize() is invoked during the lifetime of the process, or if it is the first time sqlite3_initialize() is invoked following a call to sqlite3_shutdown(). Only an effective call of sqlite3_initialize() does any initialization. All other calls are harmless no-ops.
A call to sqlite3_shutdown() is an "effective" call if it is the first call to sqlite3_shutdown() since the last sqlite3_initialize(). Only an effective call to sqlite3_shutdown() does any deinitialization. All other valid calls to sqlite3_shutdown() are harmless no-ops.
The sqlite3_initialize() interface is threadsafe, but sqlite3_shutdown() is not. The sqlite3_shutdown() interface must only be called from a single thread. All open database connections must be closed and all other SQLite resources must be deallocated prior to invoking sqlite3_shutdown().
Among other things, sqlite3_initialize() will invoke sqlite3_os_init(). Similarly, sqlite3_shutdown() will invoke sqlite3_os_end().
The sqlite3_initialize() routine returns SQLITE_OK on success. If for some reason, sqlite3_initialize() is unable to initialize the library (perhaps it is unable to allocate a needed resource such as a mutex) it returns an error code other than SQLITE_OK.
The sqlite3_initialize() routine is called internally by many other SQLite interfaces so that an application usually does not need to invoke sqlite3_initialize() directly. For example, sqlite3_open() calls sqlite3_initialize() so the SQLite library will be automatically initialized when sqlite3_open() is called if it has not be initialized already. However, if SQLite is compiled with the SQLITE_OMIT_AUTOINIT compile-time option, then the automatic calls to sqlite3_initialize() are omitted and the application must call sqlite3_initialize() directly prior to using any other SQLite interface. For maximum portability, it is recommended that applications always invoke sqlite3_initialize() directly prior to using any other SQLite interface. Future releases of SQLite may require this. In other words, the behavior exhibited when SQLite is compiled with SQLITE_OMIT_AUTOINIT might become the default behavior in some future release of SQLite.
The sqlite3_os_init() routine does operating-system specific initialization of the SQLite library. The sqlite3_os_end() routine undoes the effect of sqlite3_os_init(). Typical tasks performed by these routines include allocation or deallocation of static resources, initialization of global variables, setting up a default sqlite3_vfs module, or setting up a default configuration using sqlite3_config().
The application should never invoke either sqlite3_os_init() or sqlite3_os_end() directly. The application should only invoke sqlite3_initialize() and sqlite3_shutdown(). The sqlite3_os_init() interface is called automatically by sqlite3_initialize() and sqlite3_os_end() is called by sqlite3_shutdown(). Appropriate implementations for sqlite3_os_init() and sqlite3_os_end() are built into SQLite when it is compiled for Unix, Windows, or OS/2. When built for other platforms (using the SQLITE_OS_OTHER=1 compile-time option) the application must supply a suitable implementation for sqlite3_os_init() and sqlite3_os_end(). An application-supplied implementation of sqlite3_os_init() or sqlite3_os_end() must return SQLITE_OK on success and some other error code upon failure.