_drupal_exception_handler in includes/bootstrap.inc
Provides custom PHP exception handling.
_drupal_log_error in includes/errors.inc
Logs a PHP error or exception and displays an error page in fatal cases.
_drupal_session_write in includes/session.inc
Writes an entire session to the database (internal use only).
_drupal_shutdown_function in includes/bootstrap.inc
Executes registered shutdown functions.