一种循环队列实现方法

queue.h：

#ifndef _QUEUE_H_
#define _QUEUE_H_ 1

#ifdef __cplusplus
extern "C" {
#endif

//创建一个指定长度的循环队列，返回队列句柄。
void* queue_create(int length);

//向循环队列放入一个消息，成功返回0，队列满返回-1。
int queue_putmsg(void *handle, void *msg);

//从循环队列取出一个消息。
void* queue_getmsg(void *handle);

//销毁这个循环队列，并通过回调函数返回滞留在队列里的消息。
//注意销毁前确保 queue_putmsg() 和 queue_getmsg() 都没有调用中。
void queue_destroy(void *handle, void(*callback)(void*msg));  

#ifdef __cplusplus
}
#endif

#endif

queue.c：

#include <stdint.h>
#include <stdlib.h>
#include <pthread.h>
#include <semaphore.h>
#include "queue.h"

typedef struct {
    uint32_t        head;      // 循环队列头虚拟位置
    uint32_t        tail;      // 循环队列尾虚拟位置
    uint32_t        count;     // 循环队列已有消息个数
    uint32_t        length;    // 循环队列总长度
    sem_t           wait;      // 信号量
    pthread_mutex_t lock;      // 互斥锁
    void*           array[0];  // 消息列表
} QUEUE_T;


void* queue_create(int length){
    if(length <= 0) return NULL;
    QUEUE_T *queueCtx = calloc(1, sizeof(QUEUE_T)+sizeof(void*)*(length+1));
    if(queueCtx == NULL) return NULL;
    queueCtx->head = 0;
    queueCtx->tail = 0;
    queueCtx->count = 0;
    queueCtx->length = length;
    sem_init(&(queueCtx->wait), 0, 0);
    pthread_mutex_init(&(queueCtx->lock), NULL);
    return queueCtx;
}

int queue_putmsg(void *handle, void *msg){
    QUEUE_T *queueCtx = handle;
    int queueFull = 1;
    pthread_mutex_lock(&(queueCtx->lock));
        if(queueCtx->count < queueCtx->length){
            queueCtx->array[queueCtx->tail % queueCtx->length] = msg;
            queueCtx->count += 1;
            queueCtx->tail += 1;
            queueFull = 0;
        }
    pthread_mutex_unlock(&(queueCtx->lock));
    if(queueFull){
        return -1;
    }else{
        sem_post(&(queueCtx->wait));
        return 0;
    }
}

void* queue_getmsg(void *handle){
    QUEUE_T *queueCtx = handle;
    void *msg = NULL;
    sem_wait(&(queueCtx->wait));
    pthread_mutex_lock(&(queueCtx->lock));
        if(queueCtx->count > 0){
            msg = queueCtx->array[queueCtx->head % queueCtx->length];
            queueCtx->array[queueCtx->head % queueCtx->length] = NULL;
            queueCtx->count -= 1;
            queueCtx->head += 1;
        }
        if(queueCtx->count == 0){
            queueCtx->head = 0;
            queueCtx->tail = 0;
        }
    pthread_mutex_unlock(&(queueCtx->lock));
    return msg;
}

void queue_destroy(void *handle, void(*callback)(void*msg)){
    QUEUE_T *queueCtx = handle;
    if(callback){
        int end = 0;
        void *msg = NULL;
        while(end == 0){
            pthread_mutex_lock(&(queueCtx->lock));
            if(queueCtx->count > 0){
                msg = queueCtx->array[queueCtx->head % queueCtx->length];
                queueCtx->count -= 1;
                queueCtx->head += 1;
            }else{
                end = 1;
            }
            pthread_mutex_unlock(&(queueCtx->lock));
            if(msg){
                callback(msg);
                msg = NULL;
            }
        }
    }
    sem_destroy(&(queueCtx->wait));
    pthread_mutex_destroy(&(queueCtx->lock));
    free(queueCtx);
}

测试程序test.c：

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include "queue.h"

int main(int argc, char* argv[]){
    void *handle = queue_create(32);
    queue_putmsg(handle, "0");
    queue_putmsg(handle, "11");
    queue_putmsg(handle, "222");
    queue_putmsg(handle, "333");
    queue_putmsg(handle, "4444");
    queue_putmsg(handle, "55555");
    queue_putmsg(handle, "666666");
    queue_putmsg(handle, "7777777");
    queue_putmsg(handle, "88888888");
    queue_putmsg(handle, "999999999");
    queue_putmsg(handle, "aaaaaaaaaa");
    queue_putmsg(handle, "bbbbbbbbbbb");
    queue_putmsg(handle, "cccccccccccc");
    queue_putmsg(handle, "ddddddddddddd");
    queue_putmsg(handle, "eeeeeeeeeeeeee");
    queue_putmsg(handle, "exit");
    char *str;
    for(;;){
        str = queue_getmsg(handle);
        printf("queue_getmsg() = \"%s\"\n", str);
        if(strcmp(str, "exit") == 0){
            break;
        }
    }
    queue_destroy(handle, NULL);
    return 0;
}