동기 화 및 비동기 write 의 효율 비교 (유 닉 스 운영 체제)

#include "apue.h"
#include <sys/times.h>
#include <malloc.h>
#include <fcntl.h>
#include<string.h>

main(int argc,char *argv[])
{
    off_t lenth;
    char *buf;
    int f_out,i,k,n;
    long size;
    struct tms start,end;
    clock_t  temp;
    float utime,stime,ctime;

    if(argc==2)
    {
            if((f_out=open(argv[1],O_WRONLY|O_CREAT|O_TRUNC,FILE_MODE))==-1)
            {
                printf("Open error
");
                    exit(1);
                }
    } 
    else if(argc==3&&!strcmp(argv[2],"sync"))
    {
                if((f_out=open(argv[1],O_WRONLY|O_CREAT|O_TRUNC|O_SYNC,FILE_MODE))==-1)
                {
                    printf("Open error
");
                    exit(1);
                } 
    } 
    else
    {
            printf("Parameter input error!
");
            exit(1);
        }

    if((lenth=lseek(STDIN_FILENO,0,SEEK_END))==-1)
    {
            printf("Lseek error!
");
        }
    if(lseek(STDIN_FILENO,0,SEEK_SET)==-1)
        {
                printf("Lseek error!
");
        }

    if((buf=(char *)malloc(sizeof(char)*lenth))==NULL)
        {
            printf("Malloc error
");
            exit(1);
        }

    printf("
The length of file is %d
",lenth);

    if(read(STDIN_FILENO,buf,lenth)<0)
    {
        printf("Read error
");
        exit(1);
    }
    
    k=sysconf(_SC_CLK_TCK);
    printf("BUFFSIZE\tUSER\t\tSYSTEM\t\tCLOCK\t\tLOOP
");
    for(size=1024;size<=131072;size*=2)
    {   
        
        temp=times(&start);
        n=lenth/size;
        lseek(f_out,0,SEEK_SET);        
         for(i=0;i<n;i++)
                write(f_out,buf,size);
        if(lenth%size!=0)
                 write(f_out,buf,lenth%size);
        ctime=(float)times(&end)-temp;
        utime=(float)(end.tms_utime-start.tms_utime);
        stime=(float)(end.tms_stime-start.tms_stime);
        printf("%ld\t\t%.2f\t\t%.2f\t\t%.2f\t\t%d
",size,utime/k,stime/k,ctime/k,n);
    }
    printf("
");
}

1.   “gcc timewrite.c –o timewrite”      timewrite.c       timewrite
2.     ”./timewrite  <aa.txt  out1.txt”   “./timewrite  <aa.txt  out2.txt  sync”       。
3.         ，              。
         。       。