求助，多線程寫入文件錯(cuò)亂問題??！～～

借樓主問題，多線程加鎖的寫和單線程的寫應(yīng)該沒啥區(qū)別吧，依然是同一時(shí)刻只有一個(gè)線程在執(zhí)行寫操作，而且還會(huì)有線程切換帶來的損耗

加上線程鎖，就不會(huì)出現(xiàn)這個(gè)情況了

按照我的想法，最好上鎖然后再操作

首先, 同一個(gè)文件, 寫是獨(dú)占的, 你想同時(shí)寫, 其實(shí)也是實(shí)現(xiàn)不了的. 如果你說不同線程去操作同一個(gè)文件指針, 那么悲劇就此發(fā)生, 亂是必然的. 原因就是線程1移動(dòng)到0位置寫, 但線程1說,我要移動(dòng)到300開始寫, 最終移動(dòng)到哪里寫去了, 就要看運(yùn)氣了.

比較好的辦法是使用文件映射. 這樣不同線程就能同時(shí)寫它的不同部分了.
或者分開寫, 所有線程完成工作后,再合并到一起.

一、多線程版本
#include <stdio.h>
#include <sys/stat.h>
#include <string.h>
#include <pthread.h>
#include <unistd.h>
#include <stdlib.h>

#define BUFF_SIZE 512
#define PTHREAD_NUMBER 4

typedef struct copy_block{
    // char src[BUFF_SIZE];    //source file
    // char dest[BUFF_SIZE];    //destnation file
    FILE *src;                //source file
    FILE *dest;                //destnation file
    long start;                //begin position
    long segment_size;        //aim copy size
    int id;                    //virtual thread id
}__attribute__((packed)) Page;

long file_size(const char *filename);
void pthread_copy(void *task_info);
int multi_copy(const char *dest,const char *src);

int main(int argc,char *argv[])
{
    if(argc < 3)
    {
        fprintf(stderr,"Error params!\n");
        return 0;
    }
    char *src = argv[1];
    char *dest = argv[2];
    
    multi_copy(dest,src);
    
    return 0;
}

//get file size
long file_size(const char *filename)
{
    struct stat fstat;
    memset(&fstat,0,sizeof(fstat));
    stat(filename,&fstat);
    
    return fstat.st_size;
}

//thread task
void pthread_copy(void *task_info)
{
    //convert void * to Page *
    Page *p = (Page *)task_info;
    
    //open file for every thread
    // FILE *fin = fopen(p->src,"rb");
    // FILE *fout = fopen(p->dest,"ab+");
    
    //seek the stream to the offset
    int res_in = fseek(p->src,p->start,SEEK_SET);
    int res_out = fseek(p->dest,p->start,SEEK_SET);
    
    char buffer[BUFF_SIZE];            //buffer
    long read_size = BUFF_SIZE;        //the size for read
    long left  = p->segment_size;    //current left bytes
    long read_len = 0;                //the size has read
    long total_len = 0;                //the readed total size
    
    printf("Thread %d begin\t",p->id);
    printf("start %ld\t",p->start);
    printf("segment_size %ld\n",p->segment_size);
    // printf("src %s\t",p->src);
    // printf("dest %s\n",p->dest);
    
    //begin copy
    while(left > 0)
    {
        if(left < read_size)
        {
            read_size = left;
        }
        //read file
        read_len = fread(buffer,sizeof(char),read_size,p->src);
        total_len += read_len;
        //write file
        if(read_len > 0)
        {
            fwrite(buffer,sizeof(char),read_len,p->dest);
        }
        //the left size
        left -= read_len;
    }
    pthread_exit(NULL);
}
//create multi thread
int multi_copy(const char *dest,const char *src)
{
    //file is exists
    int file_exists = access(src,04);//read access
    if(file_exists != 0)
    {
        fprintf(stderr,"file is not exists!\n");
        return 1;
    }
    //file size
    long filesize = file_size(src);
    //pthread number
    int real_pthread_number = PTHREAD_NUMBER;
    if(filesize < BUFF_SIZE)
    {
        real_pthread_number = 1;
    }
    Page *p = (Page *)malloc(sizeof(*p) * real_pthread_number);
    
    long offset = 0;                                        //offset from file begin
    long segment = filesize / real_pthread_number;            //the bytes of every thread
    long segment_remain = filesize % real_pthread_number;    //the left bytes for the last thread
    
    //ctor the task_info
    //open file for every thread
    FILE *fin = fopen(src,"rb");
    FILE *fout = fopen(dest,"wb+");
    int i;
    for(i = 0;i < real_pthread_number;i++)
    {
        if((i + 1) == real_pthread_number)
        {
            p[i].segment_size = segment + segment_remain;
        }
        else
        {
            p[i].segment_size = segment;
        }
        //task file pointer offset
        p[i].start = offset;
        offset += p[i].segment_size;
        //file path
        // strncpy(p[i].src,src,strlen(src));
        // strncpy(p[i].dest,dest,strlen(dest));
        p[i].src = fin;
        p[i].dest = fout;
        //virtual thread id
        p[i].id = i;
    }
    //create thread
    pthread_t work[real_pthread_number];
    for(i = 0;i < real_pthread_number;i++)
    {
        pthread_create(&work[i],NULL,(void *)&pthread_copy,(void *)&p[i]);
    }
    //wait subthread exit
    for(i = 0;i < real_pthread_number;i++)
    {
        pthread_join(work[i],NULL);
    }
    //free
    if(p != NULL)
    {
        free(p);
        p = NULL;
    }
    fclose(fin);
    fclose(fout);
    
    return 0;
}

在main中以rb打開源文件,wb+打開目標(biāo)文件
修改結(jié)構(gòu)體存儲(chǔ)文件指針
在線程pthread_copy中操作文件指針位置,去除打開文件操作(在線程中以wb+打開文件會(huì)將文件截?cái)酁?)
在線程調(diào)度函數(shù)multi_copy中打開文件并在末尾關(guān)閉文件
將文件指針賦給每個(gè)線程的task_info結(jié)構(gòu)體成員

二、線程鎖版本

#include <stdio.h>
#include <sys/stat.h>
#include <string.h>
#include <pthread.h>
#include <unistd.h>
#include <stdlib.h>

#define BUFF_SIZE 512
#define PTHREAD_NUMBER 4

typedef struct copy_block{
    char src[BUFF_SIZE];    //source file
    char dest[BUFF_SIZE];    //destnation file
    long start;                //begin position
    long segment_size;        //aim copy size
    int id;                    //virtual thread id
}__attribute__((packed)) Page;

static pthread_mutex_t mut;

long file_size(const char *filename);
void pthread_copy(void *task_info);
int multi_copy(const char *dest,const char *src);

int main(int argc,char *argv[])
{
    if(argc < 3)
    {
        fprintf(stderr,"Error params!\n");
        return 0;
    }
    char *src = argv[1];
    char *dest = argv[2];
    
    multi_copy(dest,src);
    
    return 0;
}

//get file size
long file_size(const char *filename)
{
    struct stat fstat;
    memset(&fstat,0,sizeof(fstat));
    stat(filename,&fstat);
    
    return fstat.st_size;
}

//thread task
void pthread_copy(void *task_info)
{
    pthread_mutex_lock(&mut);
    //convert void * to Page *
    Page *p = (Page *)task_info;
    
    //open file for every thread
    FILE *fin = fopen(p->src,"rb");
    FILE *fout = fopen(p->dest,"rb+");
    
    if(fout == NULL)
    {
        fprintf(stderr,"Open file %s fail\n",p->dest);
        return ;
    }
    
    //seek the stream to the offset
    int res_in = fseek(fin,p->start,SEEK_SET);
    int res_out = fseek(fout,p->start,SEEK_SET);
    
    char buffer[BUFF_SIZE];            //buffer
    long read_size = BUFF_SIZE;        //the size for read
    long left  = p->segment_size;    //current left bytes
    long read_len = 0;                //the size has read
    long total_len = 0;                //the readed total size
    
    printf("Thread %d begin\t",p->id);
    printf("start %ld\t",p->start);
    printf("segment_size %ld\t",p->segment_size);
    printf("src %s\t",p->src);
    printf("dest %s\n",p->dest);
    
    //begin copy
    while(left > 0)
    {
        if(left < read_size)
        {
            read_size = left;
        }
        //read file
        read_len = fread(buffer,sizeof(char),read_size,fin);
        total_len += read_len;
        //write file
        if(read_len > 0)
        {
            fwrite(buffer,sizeof(char),read_len,fout);
        }
        //the left size
        left -= read_len;
    }
    fclose(fin);
    fclose(fout);
    pthread_mutex_unlock(&mut);
    pthread_exit(NULL);
}
//create multi thread
int multi_copy(const char *dest,const char *src)
{
    //file is exists
    int file_exists = access(src,04);//read access
    if(file_exists != 0)
    {
        fprintf(stderr,"file is not exists!\n");
        return 1;
    }
    int dest_file_exists = access(dest,04);
    if(dest_file_exists != 0)
    {
        fprintf(stderr,"File %s not exists,create it\n",dest);
        FILE *cfp = fopen(dest,"w");
        fclose(cfp);
    }
    //file size
    long filesize = file_size(src);
    //pthread number
    int real_pthread_number = PTHREAD_NUMBER;
    if(filesize < BUFF_SIZE)
    {
        real_pthread_number = 1;
    }
    Page *p = (Page *)malloc(sizeof(Page) * real_pthread_number);
    
    long offset = 0;                                        //offset from file begin
    long segment = filesize / real_pthread_number;            //the bytes of every thread
    long segment_remain = filesize % real_pthread_number;    //the left bytes for the last thread
    
    //ctor the task_info
    int i;
    for(i = 0;i < real_pthread_number;i++)
    {
        if((i + 1) == real_pthread_number)
        {
            p[i].segment_size = segment + segment_remain;
        }
        else
        {
            p[i].segment_size = segment;
        }
        //task file pointer offset
        p[i].start = offset;
        offset += p[i].segment_size;
        //file path
        strncpy(p[i].src,src,strlen(src));
        strncpy(p[i].dest,dest,strlen(dest));
        //virtual thread id
        p[i].id = i;
    }
    //create thread
    pthread_mutex_init(&mut,NULL);//init thread lock
    pthread_t work[real_pthread_number];
    for(i = 0;i < real_pthread_number;i++)
    {
        pthread_create(&work[i],NULL,(void *)&pthread_copy,(void *)&p[i]);
    }
    //wait subthread exit
    for(i = 0;i < real_pthread_number;i++)
    {
        pthread_join(work[i],NULL);
    }
    //free
    if(p != NULL)
    {
        free(p);
        p = NULL;
    }
    
    return 0;
}