Shulou(Shulou.com)06/02 Report--

It is believed that many inexperienced people don't know what to do about how to implement a circular queue in C language. therefore, this paper summarizes the causes and solutions of the problem. I hope you can solve this problem through this article.

What is a circular queue?

Ring buffer is a very typical data structure, this data structure is consistent with the producer and consumer model, it can be understood that it is a puddle, producers continue to pour water into it, consumers continue to take water out of it.

Then someone might ask, why do you need to open up a buffer memory space when you need to irrigate and take out water? Just connect the tail of the producer pipe to the head of the consumer pipe directly, which can save space.

The answer is no. Producers do not know the speed at which producers produce water, and consumers do not know the speed at which consumers consume water. If you forcibly connect it together, because the speed of production and consumption is different, there is very likely to be a water pipe explosion. Do you think this is dangerous?

Under the framework of audio system, alsa uses ring queues. When the speed of producers and consumers do not match, there will be the problem of xrun. Characteristics of ring queue 1. Array construction of ring buffer

Suppose we use an array to construct a ring cache, as shown in the following figure

We need several things to describe the ring buffer, one for the read position, one for the write position, and one for the length of the ring buffer.

From the picture, we know that the read and write position of this ring buffer points to the first address of the array, and the length of the ring buffer is 5.

So how to tell if the ring buffer is empty?

If R = W means the read and write position is the same, then the ring buffer is empty

So how do you tell if the ring buffer is full?

If (W-R) = Len, the ring buffer is full.

2. Write 3 pieces of data to the ring buffer

After writing three pieces of data, the value of W is equal to 3 and R is still equal to 0.

Three penguins have been arranged.

3. Read 2 pieces of data from the ring buffer

After reading out two pieces of data, R = 2, at this time, W is still equal to 3, after all, no more data has been written.

4. Write 3 more pieces of data

If W > LEN, how do you find the original position? This needs to be calculated. The position of the W%LEN is where the data is put, 6% 5 = 1.

5. Write another piece of data

At this time, the ring queue is full. If you want to write data again, you can't do it. (W-R) = 5 = = LEN

Code implementation / * the simplest ringbuff has more room for improvement. You can leave a message * /

# include "stdio.h"

# include "stdlib.h"

# define LEN 10

/ * Ring queue structure * /

Typedef struct ring_buff {

Int array [LEN]

Int W

Int R

} * ring

/ * Ring queue initialization * /

Struct ring_buff * fifo_init (void)

{

Struct ring_buff * p = NULL

P = (struct ring_buff *) malloc (sizeof (struct ring_buff))

If (p = = NULL)

{

Printf ("fifo_init malloc error\ n")

Return NULL

}

P-> W = 0

P-> R = 0

Return p

}

/ * determine whether the ring queue is full * /

Int get_ring_buff_fullstate (struct ring_buff * p_ring_buff)

{

/ * if the write position minus the read position is equal to the queue length, the ring queue is full * /

If ((packs ringbacks buffers-> W-packs ringbacks buffers-> R) = = LEN)

{

Return (1)

}

Else

{

Return (0)

}

}

/ * determine that the ring queue is empty * /

Int get_ring_buff_emptystate (struct ring_buff * p_ring_buff)

{

/ * if the write position is equal to the read position, the circular queue is empty * /

If (pendant ringlinks buffers-> W = = pendant ringbacks buffers-> R)

{

Return (1)

}

Else

{

Return (0)

}

}

/ * insert data * /

Int ring_buff_insert (struct ring_buff * pendant ringbacks buffminator int data)

{

If (p_ring_buff = = NULL)

{

Printf ("p null\ n")

Return (- 1)

}

If (get_ring_buff_fullstate (p_ring_buff) = = 1)

{

Printf ("buff is full\ n")

Return (- 2)

}

Pendant ringed buffs-> array [p _ ring_buff- > W%LEN] = data

Pendant ringed buffs-> W + +

/ / printf ("inset:%d% d\ n", data,p_ring_buff- > W)

Return (0)

}

/ * read ring queue data * /

Int ring_buff_get (struct ring_buff * p_ring_buff)

{

Int data = 0

If (p_ring_buff = = NULL)

{

Printf ("p null\ n")

Return (- 1)

}

If (get_ring_buff_emptystate (p_ring_buff) = = 1)

{

Printf ("buff is empty\ n")

Return (- 2)

}

Data = paired ringback buffers-> Array [p _ ring_buff- > R%LEN]

Pairringbacks buffering-> Renewal +

Return data

}

/ * destroy * /

Int ring_buff_destory (struct ring_buff * p_ring_buff)

{

If (p_ring_buff = = NULL)

{

Printf ("p null\ n")

Return (- 1)

}

Free (p_ring_buff)

Return (0)

}

Int main ()

{

Int I = 0

/ * define a ring buffer * /

Ring pt_ring_buff = fifo_init ()

/ * write data to the ring buffer * /

For (I = 0 * * R = 0)

Return p

}

/ * determine whether the ring queue is full * /

Int get_ring_buff_fullstate (struct ring_buff * p_ring_buff)

{

/ * if the write position minus the read position is equal to the queue length, the ring queue is full * /

If ((packs ringbacks buffers-> W-packs ringbacks buffers-> R) = = LEN)

{

Return (1)

}

Else

{

Return (0)

}

}

/ * determine that the ring queue is empty * /

Int get_ring_buff_emptystate (struct ring_buff * p_ring_buff)

{

/ * if the write position is equal to the read position, the circular queue is empty * /

If (pendant ringlinks buffers-> W = = pendant ringbacks buffers-> R)

{

Return (1)

}

Else

{

Return (0)

}

}

/ * insert data * /

Int ring_buff_insert (struct ring_buff * pendant ringbacks buffminator int data)

{

If (p_ring_buff = = NULL)

{

Printf ("p null\ n")

Return (- 1)

}

If (get_ring_buff_fullstate (p_ring_buff) = = 1)

{

Printf ("buff is full\ n")

Return (- 2)

}

/ / pendant ringlike buffs-> array [p _ ring_buff- > W%LEN] = data

Pendant ringed buffs-> Array [p _ ring_buff- > W & (LEN-1)] = data

Pendant ringed buffs-> W + +

/ / printf ("inset:%d% d\ n", data,p_ring_buff- > W)

Return (0)

}

/ * read ring queue data * /

Int ring_buff_get (struct ring_buff * p_ring_buff)

{

Int data = 0

If (p_ring_buff = = NULL)

{

Printf ("p null\ n")

Return (- 1)

}

If (get_ring_buff_emptystate (p_ring_buff) = = 1)

{

Printf ("buff is empty\ n")

Return (- 2)

}

/ / data = paired ringback buffering-> Array [p _ ring_buff- > R%LEN]

Data = paired ringback buffers-> Array [p _ ring_buff- > R & (LEN-1)]

Pairringbacks buffering-> Renewal +

Return data

}

/ * destroy * /

Int ring_buff_destory (struct ring_buff * p_ring_buff)

{

If (p_ring_buff = = NULL)

{

Printf ("p null\ n")

Return (- 1)

}

Free (p_ring_buff)

Return (0)

}

Int main ()

{

Int I = 0

/ * define a ring buffer * /

Ring pt_ring_buff = fifo_init ()

/ * write data to the ring buffer * /

For (I = 0 position I)

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