<2014 05 16> 线性表、栈与队列——一个环形队列的C语言实现

　　栈与队列都是具有特殊存取方式的线性表，栈属于先进后出（FILO），而队列则是先进先出（FIFO）。栈能够将递归问题转化为非递归问题，这是它的一个重要特性。除了FILO、FIFO这样的最普遍存取方式外，还有一些扩展的数据结构，如双端队列、双栈、超队列、超栈等，它们是一种扩展与变异结构。

　　线性表有顺序存储和链接存储两类，这是针对计算机的线性存储空间作出的分类。前者可以是数组，后者可以是链表。字符串是线性表最常见的应用。

　　这里我用C语言实现了一个基于数组环形队列，它具有固定的队列空间。相比于链表实现，它非常小巧和高效，特别是在负载可预计的情况下。

//fifo.h
#ifndef __FIFO_H__
#define __FIFO_H__

#define FIFO_LENGTH 20
#define EMPTY    0x00
#define FULL    0x01
#define NORMAL  0x02

typedef struct require_fifo{
    int item[FIFO_LENGTH];
    int read_ptr;
    int write_ptr;
    int flag;
}fifo;

extern fifo* fifo_create(void);
extern void fifo_destroy(fifo* fifo_ptr);
extern void fifo_in(fifo* fifo_ptr, int data);
extern int fifo_out(fifo* fifo_ptr);

#endif

//fifo.c
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <memory.h>
#include "fifo.h"

fifo* fifo_create(void);
void fifo_destroy(fifo* fifo_ptr);
void fifo_in(fifo* fifo_ptr, int data);
int fifo_out(fifo* fifo_ptr);

fifo* fifo_create(void){
    fifo *fifo_ptr = malloc(sizeof(fifo));
    memset(fifo_ptr, 0, sizeof(fifo));
    fifo_ptr->write_ptr = 0;
    fifo_ptr->read_ptr = 0;
    fifo_ptr->flag = EMPTY;
    return fifo_ptr;
}

void fifo_destroy(fifo* fifo_ptr){
    free(fifo_ptr);
    printf("destroy fifo 
");
}

void fifo_in(fifo* fifo_ptr, int data){
    if(fifo_ptr->flag != FULL ){
        fifo_ptr->item[fifo_ptr->write_ptr] = data;
        fifo_ptr->write_ptr ++;
        fifo_ptr->write_ptr %= FIFO_LENGTH;
        if((fifo_ptr->write_ptr - fifo_ptr->read_ptr) == -1){
            fifo_ptr->flag = FULL;
        }else{
            fifo_ptr->flag = NORMAL;
        }
        //printf("write_ptr = %d 
", fifo_ptr->write_ptr);
    }else{
        printf("fifo is full, write invalide
");
    }
}

int fifo_out(fifo* fifo_ptr){
    int data = 0;

    if(fifo_ptr->flag != EMPTY){
        data = fifo_ptr->item[fifo_ptr->read_ptr];
        fifo_ptr->read_ptr ++;
        fifo_ptr->read_ptr %= FIFO_LENGTH;
        if((fifo_ptr->write_ptr - fifo_ptr->read_ptr) == 0){
            fifo_ptr->flag = EMPTY;    
        }
        //printf("read_ptr = %d 
", fifo_ptr->read_ptr);
        return data;
    }else{
        printf("fifo is empty, read invalide
");
        return -1;
    }

    return -1;
}

　　我们可以写一个测试代码来测试它的性能：

#include <stdio.h>
#include <pthread.h>
#include <signal.h>
#include <unistd.h>
#include <sys/types.h>
#include "../fifo.h"

pthread_mutex_t lock_fifo;
fifo* myfifo;

void * producer_thread1(void *pin){
    pin = NULL;
    while(1){
        pthread_mutex_lock(&lock_fifo);
        fifo_in(myfifo, 1);
        pthread_mutex_unlock(&lock_fifo);
        printf("producer1 put 1 into myfifo
");
        usleep(2000000);
    }
        return((void*)0);
}

void * producer_thread2(void *pin){
    pin = NULL;
    while(1){
        pthread_mutex_lock(&lock_fifo);
        fifo_in(myfifo, 2);
        pthread_mutex_unlock(&lock_fifo);
        printf("producer2 put 2 into myfifo
");
        usleep(1500000);
    }
        return((void*)0);
}

void * consumer_thread1(void *pin){
    int require = 0;
    pin = NULL;
    
    while(1){
        pthread_mutex_lock(&lock_fifo);
        require = fifo_out(myfifo);
        pthread_mutex_unlock(&lock_fifo);
        printf("    consumer1 get %d form myfifo
", require);
        usleep(1000000);
    }
        return((void*)0);
}

void * consumer_thread2(void *pin){
    int require = 0;
    pin = NULL;
    
    while(1){
        pthread_mutex_lock(&lock_fifo);
        require = fifo_out(myfifo);
        pthread_mutex_unlock(&lock_fifo);
        printf("    consumer2 get %d form myfifo
", require);
        usleep(1000000);
    }
        return((void*)0);
}

void keyboard_exit(int signo){
    printf("exit by keyboard 
");
    fifo_destroy(myfifo);
    _exit(0);
}

int main(){
    pthread_t th_producer1, th_producer2, th_consumer1, th_consumer2;
    void * ret;
    
    pthread_mutex_init(&lock_fifo, NULL);
    myfifo = fifo_create();
    signal(SIGINT, keyboard_exit);
    pthread_create(&th_producer1, NULL, producer_thread1, 0);    
    pthread_create(&th_producer2, NULL, producer_thread2, 0);    
    pthread_create(&th_consumer1, NULL, consumer_thread1, 0);    
    pthread_create(&th_consumer2, NULL, consumer_thread2, 0);    
    
    pthread_join(th_producer1, &ret);
    pthread_join(th_producer2, &ret);
    pthread_join(th_consumer1, &ret);
    pthread_join(th_consumer2, &ret);

    while(1){
        printf("thread error
");
    }
    return 1;
}

　　写一个gcc的Makefile文件来编译链接：

CC = gcc
CFLAGS := -g -Wall 
LIB := -lpthread 
OBJ = ../fifo.o ./test.o
all: demo

demo:test fifo
    $(CC) $(CFLAGS) -o ./demo $(OBJ) $(LIB)

test:
    $(CC) $(CFLAGS) -o ./test.o -c ./test.c
fifo:
    $(CC) $(CFLAGS) -o ../fifo.o -c ../fifo.c

clean:
    rm ./test.o ./demo ../fifo.o


.PHONY: $(PHONY) clean

　　在test目录下运行./demo。

　　输出结果：

                            write_ptr = 1 
producer1 put 1 into myfifo
                            write_ptr = 2 
producer2 put 2 into myfifo
                            read_ptr = 1 
    consumer1 get 1 form myfifo
                            read_ptr = 2 
    consumer2 get 2 form myfifo
fifo is empty, read invalide
    consumer1 get -1 form myfifo
fifo is empty, read invalide
    consumer2 get -1 form myfifo
                            write_ptr = 3 
producer2 put 2 into myfifo
                            write_ptr = 4 
producer1 put 1 into myfifo
                            read_ptr = 3 
    consumer1 get 2 form myfifo
                            read_ptr = 4 
    consumer2 get 1 form myfifo
                            write_ptr = 5 
producer2 put 2 into myfifo
                            read_ptr = 5 
。。。。
。。。。
^Cexit by keyboard 
destroy fifo