Enters the monitor. If the monitor is acquired by another thread this function waits until the monitor is released. The current thread then acquires the monitor. Calls to enter# and leave# may be nested.
Referenced by GMonitorLock::GMonitorLock(), DjVuFile::notify_chunk_done(), operator=(), DjVuFile::reset(), DjVuFile::start_decode(), test_and_modify(), wait_and_modify(), DjVuDocument::wait_for_complete_init(), and DjVuDocument::wait_get_pages_num().