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按照linux内核对kfifo的实现，修改成用户空间的kfifo，kfifo是一个循环存储队列，队列是一个大块内存，通过in和out指针管理进和出队列。比较适合大小固定的数据存储。这里的实现没有加锁机制！内核kfifo原理，参考
kfifo头文件。
#ifndef _Linux_KFIFO_H#define _Linux_KFIFO_H#define __u32 unsigned long#define __u64 unsigned long long#define min(x,y) ((x) < (y) ? (x) : (y) )#define max(x,y) ((x) > (y) ? (x) : (y) )/*static inline int fls(int x){ int r; __asm__("bsrl %1,%0nt" "jnz 1fnt" "movl $-1,%0n" "1:" : "=r" (r) : "rm" (x)); return r+1;}*/static inline int fls(int x){ int r = 32; if (!x) return 0; if (!(x & 0xffff0000u)) { x <<= 16; r -= 16; } if (!(x & 0xff000000u)) { x <<= 8; r -= 8; } if (!(x & 0xf0000000u)) { x <<= 4; r -= 4; } if (!(x & 0xc0000000u)) { x <<= 2; r -= 2; } if (!(x & 0x80000000u)) { x <<= 1; r -= 1; } return r;}static inline int fls64(__u64 x){ __u32 h = x >> 32; if (h) return fls(h) + 32; return fls(x);}static inline unsigned fls_long(unsigned long l){ if (sizeof(l) == 4) return fls(l); return fls64(l);}static inline unsigned long roundup_pow_of_two(unsigned long x){ return 1UL << fls_long(x - 1);}struct kfifo { unsigned char *buffer; /* the buffer holding the data */ unsigned int size; /* the size of the allocated buffer */ unsigned int in; /* data is added at offset (in % size) */ unsigned int out; /* data is extracted from off. (out % size) */};struct kfifo *kfifo_init(unsigned char *buffer, unsigned int size);struct kfifo *kfifo_alloc(unsigned int size);void kfifo_free(struct kfifo *fifo);unsigned int __kfifo_put(struct kfifo *fifo, unsigned char *buffer, unsigned int len);unsigned int __kfifo_get(struct kfifo *fifo, unsigned char *buffer, unsigned int len);static inline void __kfifo_reset(struct kfifo *fifo){ fifo->in = fifo->out = 0;}static inline void kfifo_reset(struct kfifo *fifo){ __kfifo_reset(fifo);}static inline unsigned int kfifo_put(struct kfifo *fifo, unsigned char *buffer, unsigned int len){ unsigned int ret; ret = __kfifo_put(fifo, buffer, len); return ret;}static inline unsigned int kfifo_get(struct kfifo *fifo, unsigned char *buffer, unsigned int len){ unsigned int ret; ret = __kfifo_get(fifo, buffer, len); if (fifo->in == fifo->out) fifo->in = fifo->out = 0; return ret;}static inline unsigned int __kfifo_len(struct kfifo *fifo){ return fifo->in - fifo->out;}static inline unsigned int kfifo_len(struct kfifo *fifo){ unsigned int ret; ret = __kfifo_len(fifo); return ret;}#endifkfifo实现 #include "kfifo.h"#includekfifo测试（来自网友的代码）#include #include struct kfifo *kfifo_init(unsigned char *buffer, unsigned int size){ struct kfifo *fifo; fifo = (struct kfifo *)malloc(sizeof(struct kfifo)); if (!fifo) return NULL; fifo->buffer = buffer; fifo->size = size; fifo->in = fifo->out = 0; return fifo;}struct kfifo *kfifo_alloc(unsigned int size){ unsigned char *buffer; struct kfifo *ret; if (size & (size - 1)) { fprintf(stderr,"size > 0x80000000n"); size = roundup_pow_of_two(size); } buffer = (unsigned char *)malloc(size); if (!buffer) return NULL; ret = kfifo_init(buffer, size); if ((unsigned long)ret <= 0) { free(buffer); } return ret;}void kfifo_free(struct kfifo *fifo){ free(fifo->buffer); free(fifo);}unsigned int __kfifo_put(struct kfifo *fifo, unsigned char *buffer, unsigned int len){ unsigned int l; len = min(len, fifo->size - fifo->in + fifo->out); l = min(len, fifo->size - (fifo->in & (fifo->size - 1))); memcpy(fifo->buffer + (fifo->in & (fifo->size - 1)), buffer, l); memcpy(fifo->buffer, buffer + l, len - l); fifo->in += len; return len;}unsigned int __kfifo_get(struct kfifo *fifo, unsigned char *buffer, unsigned int len){ unsigned int l; len = min(len, fifo->in - fifo->out); l = min(len, fifo->size - (fifo->out & (fifo->size - 1))); memcpy(buffer, fifo->buffer + (fifo->out & (fifo->size - 1)), l); fifo->out += len; return len;}
#define FIFO_LENGTH 4096#includeMakefile#include #include #include #include "kfifo.h"struct ll_param{ struct kfifo * fifo; int msg_len;};static struct ll_param fifo;void thread_reader(void * param){ int read_len=0; unsigned int counter=0; unsigned char buffer[FIFO_LENGTH]; struct ll_param * p=(struct ll_param *)param; printf("nnn = %d\n", roundup_pow_of_two(5)); for(;;) { bzero(buffer, FIFO_LENGTH); read_len=kfifo_get(p->fifo, buffer, 25); if(read_len !=0 ) { printf("Read len:%d, buffer is :< %s >n\n", read_len, buffer); } else { counter++; } if(counter > 20) { break; } usleep(50000); }}void thread_writer(void * param){ unsigned int write_len = 0; unsigned int counter = 0; unsigned char buffer[32]; struct ll_param * p = (struct ll_param *)param; for(counter = 0; counter < 100; counter++) { bzero(buffer,32); sprintf((char *)buffer, "This is %d message.n", counter); write_len=kfifo_put(p->fifo, buffer, 25); //strlen((char *)buffer) usleep(100); }}int main(void){ pthread_t pidr; pthread_t pidw; fifo.msg_len = 10; fifo.fifo = kfifo_alloc(FIFO_LENGTH); pthread_create(&pidw, NULL, (void *)thread_writer, &fifo); pthread_create(&pidr, NULL, (void *)thread_reader, &fifo); pthread_join(pidr, NULL); pthread_join(pidw, NULL); kfifo_free(fifo.fifo); printf("nGoodbye!n\n"); return 0;}
CFLAGS = -O2 -Wall INCLUDE = -I /CC = gcc test:test.o kfifo.o ${CC} ${CFLAGS} test.o kfifo.o -o $@ ${INCLUDE} -pthreadtest.o: $(CC) -c test.c ${INCLUDE} -pthreadkfifo.o: $(CC) -c kfifo.c ${INCLUDE}clean: rm -rf *.o test 转载地址：http://tfqci.baihongyu.com/