The realization of streaming media learning four--------ORTP queue

A common queue is implemented in ORTP, each of which consists of three entities, namely queues, message blocks, and data blocks, which correspond to queue_t, MSGB, and datab structures, respectively.

The definition of queue_t is as follows:

typedef struct _QUEUE {mblk_t _q_stopper;           /* Message Queue header */int Q_mcount; /*number of packet in the Q */} queue_t;

_q_stopper: A message block, embedded in queue_t, whose primary function is to act as a table header for the list; _q_stopper points to a mblk_t with no actual data, just as the header of the header of the message to the column. PUTQ or GETQ are all starting from the first mblk_t after _q_stopper. Q_mcount: Used to record the number of queue elements. To construct an empty message queue:
Note: void Qinit (queue_t *q) {
Mblk_init (&q->_q_stopper);
q->_q_stopper.b_next=&q->_q_stopper;
q->_q_stopper.b_prev=&q->_q_stopper;
q->q_mcount=0;
}
From the above initialization of a queue_t function can be learned that _q_stopper initialization, _q_stopper.b_next, _q_stopper.b_prev are pointing to _q_stopper their own.

The definition of mblk_t is as follows:

typedef struct MSGB {struct MSGB *b_prev;    /* Point to Previous message Block */struct MSGB *b_next;    /* point to the next message Block */struct MSGB *b_cont;  /* Compound message fast mblk_t */struct datab *b_datap;  /* Data block pointer */unsigned Char *b_rptr;  /* Data pointer read */unsigned char *b_wptr; /* Data pointer written */uint32_t reserved1;uint32_t RESERVED2;} mblk_t;

B_prev and B_next: The list pointer of the message block, in which all the message blocks are strung into chains through the two pointers. B_cout: This pointer can form a composite message block, the composite message block consists of multiple message blocks, but in the queue as an element B_DATAP: The data pointer of the message block, pointing to a data block B_RPTR: The data that points to the data block has been read part B_ WPTR: Part of the data that points to the data block has been written to reserved1 and reserved2: Reserved use

The definition of Datab is as follows:

typedef struct DATAB {unsigned char *db_base;/* Data base of data block */unsigned Char *db_lim; /* End address of the data portion of the data Block */void (*DB_FREEFN) (void *);             /* The release function of data block data */int db_ref; /* Data Block reference count */} dblk_t;

Db_base: Data base db_lim: End of data address db_freefn: function to release data for block Db_ref: reference count of data blocks

The realization of streaming media learning four--------ORTP queue