单生产者单消费者模式的无锁队列实现

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#ifndef FIFO_H#define FIFO_Hstruct FIFO{    void **buffer;    unsigned int size;    unsigned int in;    unsigned int out;};struct FIFO *FIFO_alloc(unsigned int size);unsigned int FIFO_put(struct FIFO *FIFO,  void** obj_table, unsigned int n);unsigned int FIFO_get(struct FIFO *FIFO, void** obj_table, unsigned int len);#endif // FIFO_H

#include "fifo.h"#include <stdio.h>#include <stdlib.h>#include <math.h>#define min(a, b) ((a) > (b))?(b):(a)#define max(a, b) ((a) > (b))?(a):(b)#ifdef CONFIG_X86_32/*指令“lock; addl $0,0(%%esp)”表示加锁，把0加到栈顶的内存单元，该指令操作本身无意义，但这些指令起到内存屏障的作用，让前面的指令执行完成。具有XMM2特征的CPU已有内存屏障指令，就直接使用该指令*/#define mb() alternative("lock; addl $0,0(%%esp)", "mfence", X86_FEATURE_XMM2)#define rmb() alternative("lock; addl $0,0(%%esp)", "lfence", X86_FEATURE_XMM2)#define wmb() alternative("lock; addl $0,0(%%esp)", "sfence", X86_FEATURE_XMM)#else#define mb() asm volatile("mfence":::"memory")#define rmb() asm volatile("lfence":::"memory")#define wmb() asm volatile("sfence" ::: "memory")#endifstatic inline int fls(int x){    int r;    __asm__("bsrl %1,%0\n\t"            "jnz 1f\n\t"            "movl $-1,%0\n"            "1:" : "=r" (r) : "rm" (x));    return r+1;}static inline unsigned int roundup_pow_of_two(unsigned int x){    return 1UL << fls(x - 1);}struct FIFO *FIFO_alloc(unsigned int size){    struct FIFO *ret = (struct FIFO*)malloc(sizeof(struct FIFO));    if (size & (size - 1))    {        size = roundup_pow_of_two(size);    }    ret->buffer = (void**)malloc(size*sizeof(void*));    ret->size = size;    if (!ret->buffer)    {        return NULL;    }    memset(ret->buffer, 0, size*sizeof(void*));    ret->in  = 0 ;    ret->out = 0;    return ret;}unsigned int FIFO_put(struct FIFO *FIFO,  void** obj_table, unsigned int n){    unsigned int l;    unsigned int len;    unsigned int i, nCount, nIndex;    len = min(n, FIFO->size - FIFO->in + FIFO->out);    mb();    l = min(len, FIFO->size - (FIFO->in & (FIFO->size - 1)));    nCount = l;    nIndex = FIFO->in & (FIFO->size - 1);    for(i=0; i<nCount; i++)    {        FIFO->buffer[nIndex + i] = obj_table[i];    }    nCount = len-l;    for(i=0; i<nCount; i++)    {        FIFO->buffer[i] = obj_table[l+ i];    }    wmb();    FIFO->in += len;    return len;}unsigned int FIFO_get(struct FIFO *FIFO, void** obj_table, unsigned int len){    unsigned int l;    unsigned int nCount, nIndex;    unsigned int i;    len = min(len, FIFO->in - FIFO->out);    rmb();    l = min(len, FIFO->size - (FIFO->out & (FIFO->size - 1)));    nCount = l;    nIndex = FIFO->out & (FIFO->size - 1);    for(i=0; i<nCount; i++)    {        obj_table[i] = FIFO->buffer[nIndex + i];    }    nIndex = nCount;    nCount = len - l;    for(i=0; i<nCount; i++)    {        obj_table[nIndex + i] = FIFO->buffer[i];    }    mb();    FIFO->out += len;    return len;}

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