tailieunhanh - BLUETOOTH APPLICATION PROGRAMMING WITH THE JAVA APIS ESSENTIALS EDITION PHẦN 9

nó tìm thấy một thiết bị Bluetooth cụ thể hoặc nếu ứng dụng bị tạm dừng hoặc bị phá hủy. CancelInquiry () phương pháp hủy bỏ một cuộc điều tra. Để ngăn chặn một ứng dụng từ hủy bỏ cuộc điều tra của Bluetooth khác Lập trình với các API | 230 Chapter Eight L2CAP L2CAP buffers fill up. When buffers are going to overflow the only options available to L2CAP are the following Let the lower-level flow control mechanisms kick in and shut off all incoming packets over this ACL link. Baseband flow control shuts off L2CAP packets over all the L2CAP channels not just the L2CAP channels that are having trouble keeping up. Discard some L2CAP packets because there is no room for them in the L2CAP buffers. The lower stack layers will not retransmit these packets because they have already been acknowledged as successfully received. Simply discarding L2CAP packets is an unattractive option that would lead to data corruption or hung communications. However the other option whereby the lower-level flow control shuts off all of the L2CAP channels can lead to deadlock in certain situations. The same problem of a multiplexing layer over a reliable communication layer arises in infrared data communications. The deadlock scenario for the IrDA protocol stack is discussed by Williams and Millar 46 . A summary of the deadlock scenario in L2CAP terms is as follows Suppose a higher-level application uses two L2CAP channels. One of the L2CAP channels is used as a data channel and the other L2CAP channel is used as a signaling channel. It is possible that the L2CAP buffers are overflowing because the application is waiting to receive an L2CAP packet on the signaling channel before it processes the packets on the data channel. If this is the case and if baseband flow control shuts off the entire ACL link then the L2CAP packet on the signaling channel cannot get through. The application continues to wait for this packet so it does not process the packets on the data channel. However processing packets on the data channel is the only thing that will free L2CAP buffers and get packets flowing again on the ACL link. Because the original L2CAP specification had no flow control the protocols and profiles that use L2CAP communications .