读书人
栏目▼

生产者消费者有关问题中缓冲区的读写

发布时间： 2013-01-09 09:38:16 作者： rapoo

生产者消费者问题中，缓冲区的读写问题
linux下gcc；
5个生产者线程，5个消费者线程，生产者从1开始写，一直写到500。
用一个结构体数据模拟读写缓冲区，每写一次对其遍历排序一次，将未被读取的数据置前。

问题：
（消费线程中）
当一个消费者线程持续获取缓冲区锁 并占有时，出现读取数据失败的情况。
（ps:消费线程切换则不会出现这种情况；
可能描述比较模糊，运行一下就能看到现象了，生产者消费者有关问题中，缓冲区的读写有关问题！）

#include "common.h"

//common中含头文件和 模拟缓冲区的结构体s_client
/*
#include <sys/un.h>
#include <unistd.h>
#include <stdlib.h>
#include <pthread.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <string.h>
#include <semaphore.h>

typedef struct s_client
{
int clientid;//数值
int status;//标示是否有值，有值=1，无值=0
};
*/

//main.c
#define MAX_CONSUMERS 5 //消费线程数
#define MAX_PRODUCERS 5 //生产线程数
#define MAX_BUFFERS 20 //缓冲区可存数据
#define MAX_NUMBER 500 //生产总数

FILE *fp, *fp_out, *fp_in;//可无视，in.txt 与 123.txt 结合stdout 可看出问题点buff内数据>2

pthread_mutex_t full_mutex,empty_mutex,file_mutex;
//分别为消费、生产、缓冲区互斥锁

volatile int buff_counts = 0, exit_flag = 0, i_in = 0, exit_flag_consumer = 0;
//exit_flag、exit_flag_consumer分别为生产、消费线程退出条件，i_in 取值 1至500

volatile struct s_client buff[MAX_BUFFERS]; //读写缓冲区

//生产者写缓冲区
int write_one(volatile struct s_client *buffer, int num)
{
int i,j,sum=0;

//遍历，将未被读取的数据置前
for(i=0;i<MAX_BUFFERS;i++)
{
if(buffer[i].status) continue;

for(j=i+1;j<MAX_BUFFERS;j++)
{
if(buffer[j].status )
{
buffer[i].status = 1;
buffer[i].clientid = buffer[j].clientid;
buffer[j].status = 0;
buffer[j].clientid = 0;
}
}
}
for(i=0;i<MAX_BUFFERS;i++)
{
if(buffer[i].status == 0 )
{
buffer[i].clientid = num;
buffer[i].status = 1;
fprintf(fp_in, "buffer[%d].clientid = %d\n",i,num);
break;
}
}
return 0;
}

//消费者读缓冲区
int get_one(volatile struct s_client *buffer)
{
int i,num = -1;
for(i = 0; i < MAX_BUFFERS; i++)


{
if(buffer[i].status)
{
num = buffer[i].clientid ;
buffer[i].status = 0;
//fprintf(fp_in, "buffer[%d].clientid = %d\n",i,num);
break;
}
//return -1;
}
return num;
}

//生产者线程
int producer()
{

printf("%4d produce is begain\n", pthread_self()%10000);
fprintf(fp_out, "%4d produce is begain\n", pthread_self()%10000);
while(1)
{
pthread_mutex_lock(&empty_mutex);
while(buff_counts<MAX_BUFFERS)
{
i_in++;
if(i_in>MAX_NUMBER || exit_flag)
{
exit_flag = 1;
break;
}

pthread_mutex_lock(&file_mutex);
fprintf(fp,"%d\n", i_in);
//fflush(fp);
write_one(buff, i_in);
buff_counts++;
pthread_mutex_unlock(&file_mutex);

//printf("pid=%04d producet %d \n", pthread_self()%10000, i_in);
fprintf(fp_out, "pid=%04d producet %d \n", pthread_self()%10000, i_in);
usleep(1000);
}
pthread_mutex_unlock(&empty_mutex);
//usleep(10000);
if(i_in>MAX_NUMBER || exit_flag) break;
}
printf("producer %04d exited!\n", pthread_self()%10000);
fprintf(fp_out, "producer %04d exited!\n", pthread_self()%10000);
pthread_exit("produce over!");
}

//消费者线程
int consumer()
{
int i;
while(1)
{
pthread_mutex_lock(&full_mutex);

while(buff_counts>0)
{


if(exit_flag_consumer) break;

pthread_mutex_lock(&file_mutex);
i = get_one(buff);
if(i<0)
{
printf("get_one failed!\n");
pthread_mutex_unlock(&file_mutex);
continue;
}
fprintf(fp, "buff_counts = %d //pid=%04d consume %d\n", buff_counts, pthread_self()%10000,i);
if(i==MAX_NUMBER)
{
exit_flag_consumer = 1;
}
printf("pid=%04d consume %d\n", pthread_self()%10000,i);
buff_counts--;
pthread_mutex_unlock(&file_mutex);

if(exit_flag_consumer)
{
exit_flag = 1;
break;
}
//usleep(1000);
//this sentence will make the get_one(buff) failed in the old thread
//问题出现在这里，如果这里用usleep，这一个消费者线程继续读取的缓冲区buff会失败（当缓冲区多余2个以上数据时）
//若不使用usleep，其他消费者线程获取缓冲区锁，不会出现读取失败的问题。
}
pthread_mutex_unlock(&full_mutex);
if(i==MAX_NUMBER || exit_flag) break;
usleep(1000);
}
printf("consumer %04d exited!\n", pthread_self()%10000);
pthread_exit("consume over!");
}

int main(int argc, int argv[])
{
pthread_t consumer_queue[MAX_CONSUMERS], producer_queue[MAX_PRODUCERS];
int i,result;
char temp[10];
void *message;

memset((void *)buff,0,sizeof(buff));
fp = fopen("./123.txt", "wr+");
fp_in = fopen("./in.txt", "w+");
fp_out = fopen("./out.txt", "w+r");
if(!fp)


{
perror("fopen failed!");
exit(1);
}
result = pthread_mutex_init(&full_mutex, NULL);
if(result)
{
perror("pthread_mutex_init failed!");
exit(1);
}

result = pthread_mutex_init(&empty_mutex, NULL);
if(result)
{
perror("pthread_mutex_init failed!");
exit(1);
}

result = pthread_mutex_init(&file_mutex, NULL);
if(result)
{
perror("pthread_mutex_init failed!");
exit(1);
}

//消费线程
for(i = 0; i<MAX_CONSUMERS; i++)
{
result = pthread_create(&consumer_queue[i], NULL, (void *)consumer, NULL);
if(result)
{
perror("pthread_create failed!");
exit(1);
}
}
//生产线程
for(i = 0; i<MAX_PRODUCERS; i++)
{
result = pthread_create(&producer_queue[i], NULL, (void *)producer, NULL);
if(result)
{
perror("pthread_create failed!");
exit(1);
}
}
for(i = MAX_PRODUCERS-1; i>=0; i--)
{
pthread_join(producer_queue[i], &message);
printf("return message is: %s\n", (char*)message);
}
sleep(1);
fclose(fp);
exit(0);

}

[解决办法]
仅供参考

//循环向a函数每次发送200个字节长度（这个是固定的）的buffer,
//a函数中需要将循环传进来的buffer，组成240字节（也是固定的）的新buffer进行处理，
//在处理的时候每次从新buffer中取两个字节打印
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <windows.h>
#include <process.h>
#include <io.h>
//Log{
#define MAXLOGSIZE 10000000
#define ARRSIZE(x) (sizeof(x)/sizeof(x[0]))
#include <time.h>
#include <sys/timeb.h>
#include <stdarg.h>
char logfilename1[]="MyLog1.log"; 
 
char logfilename2[]="MyLog2.log";
char logstr[16000];
char datestr[16];
char timestr[16];
char mss[4];
CRITICAL_SECTION cs_log;
FILE *flog;
void Lock(CRITICAL_SECTION *l) {
    EnterCriticalSection(l);
}
void Unlock(CRITICAL_SECTION *l) {
    LeaveCriticalSection(l);
}
void LogV(const char *pszFmt,va_list argp) {
    struct tm *now;
    struct timeb tb;

    if (NULL==pszFmt
[解决办法]
0==pszFmt[0]) return;
    if (-1==_vsnprintf(logstr,ARRSIZE(logstr),pszFmt,argp)) logstr[ARRSIZE(logstr)-1]=0;
    ftime(&tb);
    now=localtime(&tb.time);
    sprintf(datestr,"%04d-%02d-%02d",now->tm_year+1900,now->tm_mon+1,now->tm_mday);
    sprintf(timestr,"%02d:%02d:%02d",now->tm_hour     ,now->tm_min  ,now->tm_sec );
    sprintf(mss,"%03d",tb.millitm);
    printf("%s %s.%s %s",datestr,timestr,mss,logstr);
    flog=fopen(logfilename1,"a");
    if (NULL!=flog) {
        fprintf(flog,"%s %s.%s %s",datestr,timestr,mss,logstr);
        if (ftell(flog)>MAXLOGSIZE) {
            fclose(flog);
            if (rename(logfilename1,logfilename2)) {
                remove(logfilename2);
                rename(logfilename1,logfilename2);
            }
            flog=fopen(logfilename1,"a");
            if (NULL==flog) return;
        }
        fclose(flog);
    }
}
void Log(const char *pszFmt,...) {
    va_list argp;

    Lock(&cs_log);
    va_start(argp,pszFmt);
    LogV(pszFmt,argp);
    va_end(argp);
    Unlock(&cs_log);
}
//Log}
#define ASIZE    200
#define BSIZE    240
#define CSIZE      2
char Abuf[ASIZE];
char Cbuf[CSIZE];
CRITICAL_SECTION cs_HEX ;
CRITICAL_SECTION cs_BBB ;
struct FIFO_BUFFER {
    int  head;
    int  tail;
    int  size;
    char data[BSIZE];
} BBB;
int No_Loop=0;
void HexDump(int cn,char *buf,int len) {
    int i,j,k;
    char binstr[80];

    Lock(&cs_HEX);
    for (i=0;i<len;i++) {
        if (0==(i%16)) { 
 
            sprintf(binstr,"%03d %04x -",cn,i);
            sprintf(binstr,"%s %02x",binstr,(unsigned char)buf[i]);
        } else if (15==(i%16)) {
            sprintf(binstr,"%s %02x",binstr,(unsigned char)buf[i]);
            sprintf(binstr,"%s  ",binstr);
            for (j=i-15;j<=i;j++) {
                sprintf(binstr,"%s%c",binstr,('!'<buf[j]&&buf[j]<='~')?buf[j]:'.');
            }
            Log("%s\n",binstr);
        } else {
            sprintf(binstr,"%s %02x",binstr,(unsigned char)buf[i]);
        }
    }
    if (0!=(i%16)) {
        k=16-(i%16);
        for (j=0;j<k;j++) {
            sprintf(binstr,"%s   ",binstr);
        }
        sprintf(binstr,"%s  ",binstr);
        k=16-k;
        for (j=i-k;j<i;j++) {
            sprintf(binstr,"%s%c",binstr,('!'<buf[j]&&buf[j]<='~')?buf[j]:'.');
        }
        Log("%s\n",binstr);
    }
    Unlock(&cs_HEX);
}
int GetFromRBuf(int cn,CRITICAL_SECTION *cs,FIFO_BUFFER *fbuf,char *buf,int len) {
    int lent,len1,len2;

    lent=0;
    Lock(cs);
    if (fbuf->size>=len) {
        lent=len;
        if (fbuf->head+lent>BSIZE) {
            len1=BSIZE-fbuf->head;
            memcpy(buf     ,fbuf->data+fbuf->head,len1);
            len2=lent-len1;
            memcpy(buf+len1,fbuf->data           ,len2);
            fbuf->head=len2;
        } else {
            memcpy(buf     ,fbuf->data+fbuf->head,lent);
            fbuf->head+=lent;
        }
        fbuf->size-=lent;
    }
    Unlock(cs);
    return lent; 
 
}
void thdB(void *pcn) {
    char        *recv_buf;
    int          recv_nbytes;
    int          cn;
    int          wc;
    int          pb;

    cn=(int)pcn;
    Log("%03d thdB              thread begin...\n",cn);
    while (1) {
        Sleep(10);
        recv_buf=(char *)Cbuf;
        recv_nbytes=CSIZE;
        wc=0;
        while (1) {
            pb=GetFromRBuf(cn,&cs_BBB,&BBB,recv_buf,recv_nbytes);
            if (pb) {
                Log("%03d recv %d bytes\n",cn,pb);
                HexDump(cn,recv_buf,pb);
                Sleep(1);
            } else {
                Sleep(1000);
            }
            if (No_Loop) break;//
            wc++;
            if (wc>3600) Log("%03d %d==wc>3600!\n",cn,wc);
        }
        if (No_Loop) break;//
    }
}
int PutToRBuf(int cn,CRITICAL_SECTION *cs,FIFO_BUFFER *fbuf,char *buf,int len) {
    int lent,len1,len2;

    Lock(cs);
    lent=len;
    if (fbuf->size+lent>BSIZE) {
        lent=BSIZE-fbuf->size;
    }
    if (fbuf->tail+lent>BSIZE) {
        len1=BSIZE-fbuf->tail;
        memcpy(fbuf->data+fbuf->tail,buf     ,len1);
        len2=lent-len1;
        memcpy(fbuf->data           ,buf+len1,len2);
        fbuf->tail=len2;
    } else {
        memcpy(fbuf->data+fbuf->tail,buf     ,lent);
        fbuf->tail+=lent;
    }
    fbuf->size+=lent;
    Unlock(cs);
    return lent;
}
void thdA(void *pcn) { 
 
    char        *send_buf;
    int          send_nbytes;
    int          cn;
    int          wc;
    int           a;
    int          pa;

    cn=(int)pcn;
    Log("%03d thdA              thread begin...\n",cn);
    a=0;
    while (1) {
        Sleep(100);
        memset(Abuf,a,ASIZE);
        a=(a+1)%256;
        if (16==a) {No_Loop=1;break;}//去掉这句可以让程序一直循环直到按Ctrl+C或Ctrl+Break或当前目录下存在文件No_Loop
        send_buf=(char *)Abuf;
        send_nbytes=ASIZE;
        Log("%03d sending %d bytes\n",cn,send_nbytes);
        HexDump(cn,send_buf,send_nbytes);
        wc=0;
        while (1) {
            pa=PutToRBuf(cn,&cs_BBB,&BBB,send_buf,send_nbytes);
            Log("%03d sent %d bytes\n",cn,pa);
            HexDump(cn,send_buf,pa);
            send_buf+=pa;
            send_nbytes-=pa;
            if (send_nbytes<=0) break;//
            Sleep(1000);
            if (No_Loop) break;//
            wc++;
            if (wc>3600) Log("%03d %d==wc>3600!\n",cn,wc);
        }
        if (No_Loop) break;//
    }
}
int main() {
    InitializeCriticalSection(&cs_log );
    Log("Start===========================================================\n");
    InitializeCriticalSection(&cs_HEX );
    InitializeCriticalSection(&cs_BBB );

    BBB.head=0;
    BBB.tail=0;
    BBB.size=0;

    _beginthread((void(__cdecl *)(void *))thdA,0,(void *)1);
    _beginthread((void(__cdecl *)(void *))thdB,0,(void *)2);

    if (!access("No_Loop",0)) {
        remove("No_Loop");
        if (!access("No_Loop",0)) {
            No_Loop=1;
        } 
 
    }
    while (1) {
        Sleep(1000);
        if (No_Loop) break;//
        if (!access("No_Loop",0)) {
            No_Loop=1;
        }
    }
    Sleep(3000);
    DeleteCriticalSection(&cs_BBB );
    DeleteCriticalSection(&cs_HEX );
    Log("End=============================================================\n");
    DeleteCriticalSection(&cs_log );
    return 0;
}

读书人网 >C语言

热点推荐

触屏版 | 电脑版

读书人网 m.reader8.net