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Message Buffer

Message Buffer. Nguyễn Hoàng Tâm 50702111 Nguyễn Văn Trọng 50702651. Using message buffer. Synchronization and communication : Passing variable-size messages Holding messages for sending and receiving

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Message Buffer

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  1. Message Buffer Nguyễn Hoàng Tâm 50702111 Nguyễn Văn Trọng 50702651

  2. Using message buffer • Synchronization and communication : • Passing variable-size messages • Holding messages for sending and receiving • 2 queues : messages waiting to be sent ( send queue),tasks waiting for messages receipt ( receive queue).

  3. Message sender and receipt • Sender : • Copy message to buffer • If not enough space : • message is queued for sending until enough space is available. • task waiting to send is put in send queue

  4. Message sender and receipt • Receipt : • Message is fetched from buffer • If buffer has no messages : task enter Wait state and put in receive queue • What if buffer size is 0 : • Message communication function is synchronous • Task wait for system call to be invoked • Message is passed when both side issue system call

  5. Synchronous Communication by Message Buffer

  6. Functions tk_cre_mbf : create message buffer • ID mbfid = tk_cre_mbf(T_CMBF *pk_cmbf) • pk_cmbf details : • VP exinf Extended informations • ATR mbfatr Message buffer attributes • INT bufsz Message buffer size ( in bytes ) • INT maxmsz Maximun massage size (in bytes )

  7. Functions Error code : - E_OK Normal completion - E_NOMEM Insufficient memory (memory for control block or ring buffer area cannot be allocated) - E_LIMIT Number of message buffers exceeds the system limit - E_RSATR Reserved attribute (mbfatr is invalid or cannot be used) - E_PAR Parameter error (pk cmbf is invalid, or bufsz or maxmsz is negative or invalid) mbfatr : - TA_TFIFO Tasks waiting to send are queued in FIFO order - TA_TPRI Tasks waiting to send are queued in priority order - TA_NODISWAI Wait disabling by tk dis wai is prohibited

  8. Functions • Notes : • Tasks waiting for a message to be sent can be designated in TA_FIFO or TA_PRI • Messages are queued in FIFO order only • Tasks waiting for message receipt are queued in FIFO order only • When there’re multiple tasks waiting to send , the order will always be obeyed in spite of buffer space ( enough or not )

  9. Functions tk_del_mbf : delete message buffer • ER recd = tk_del_mbf(ID mbfid) Error code : - E_OK : Normal completion - E_ID : Invalid ID number (mbfid is invalid or cannot be used) - E_NOEXS : Object does not exist (the message buffer designated in mbfid does not exist)

  10. Functions When this functions is called : • Release : message buffer space and control block • If there’re tasks queued in message buffer, error code E_DLT returned to the tasks in Wait state • If there’re message in buffer, it is deleted and no error code is returned

  11. Functions tk_snd_mbf : send message to message buffer • ER ercd = tk_snd_mbf ( ID mbfid, VP msg, INT msgsz, TMO tmout ) • Parameter : - ID mbfid Message buffer ID - INT msgsz Send message size (in bytes) - VP msg Start address of send message packet - TMO tmout Timeout designation

  12. Functions Error code : - E_OK :Normal completion - E_ID :Invalid ID number (mbfid is invalid or cannot be used) - E_NOEXS : Object does not exist (the message buffer designated in mbfid does not exist) - E_PAR : Parameter error (msgsz · 0, msgsz > maxmsz,value that cannot be used in msg, or tmout · (¡2)) - E_DLT : The object being waited for was deleted (message buffer was deleted while waiting) - E_RLWAI : Wait state released (tk rel wai received in wait state) - E_DISWAI : Wait released by wait disabled state - E_TMOUT : Polling failed or timeout - E_CTX : Context error (issued from task-independent portion or in dispatch disabled state)

  13. Functions • Descriptions : • Copy msgsz bytes starting at mgz to message queue of message buffer • If msgsz is larger than maxmsz , error code is returned • If not enough space, task issued this system call goes to wait state • If tmout elapses before wait state releases , system call terminates and return error code • When tmout = T_POL , if there’s enough space, error code return without entering wait state • When tmout = T_FEVR , task continues to wait for buffer space become available

  14. Functions tk_recv_mbf : receive message buffer • INT msgsz = tk_rcv_mbf ( ID mbfid, VP msg, TMO tmout ) Return message size or error code - Parameter, error code : similar to tk_snd_mbf

  15. Functions tk_ref_mbf : get message buffer status • ER ercd = tk_ref_mbf ( ID mbfid, T_RMBF *pk_rmbf ) • Pk_rmbf details : • VP exinf :Extended information • ID wtsk :Waiting task information • ID stsk :Send task information • INT msgsz :Size of the next message to be received (in bytes) • INT frbufsz :Free buffer size (in bytes) • INT maxmsz :Maximum message size (in bytes)

  16. Functions • Descriptions : • Reference the status of message buffer • If multiple tasks are waiting , return the ID of task at the head of queue • If no task waiting , 0 is returned • If there’s no message at the queue, msgsz = 0 is returned

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