体会 CPU 虚拟化，同时运行许多程序
cpu.c

#include<stdio.h>
#include<stdlib.h>
#include<sys/time.h>
#include<assert.h>
#include <unistd.h>
int main(int argc,char* argv[]){
    if(argc != 2){
        fprintf(stderr,"usage:cpu<string>\n");
    }
    char *str = argv[1];
    while (1)
    {
        sleep(1);
        printf("%s\n",str);
    }
    return 0;
}

程序的单个实例

进程的多个实例

./cpu A & ./cpu B & ./cpu C & ./cpu D & 

运行多个实例的时候，无法通过 ctrl + c 使得进程停止。只能在另外的终端通过 kill -9 （pid） 终止进程。

mem.c

#include<unistd.h>
#include<stdio.h>
#include<stdlib.h>
#include<assert.h>
int main(int argc,char *argv[]){
    int *p = (int*)malloc(sizeof(int));
    assert(p != NULL);
    printf("(%d) memory address of p:%08x\n",getpid(),(unsigned long)p);
    //printf("(%d) memory address of p:%08x\n",getpid(),(unsigned)p);
    //cast from ‘int*’ to ‘unsigned int’ loses precision [-fpermissive]
    //主要是 8 字节的指针转化为 unsigned（4字节），不符合转换的精度，
    //应该转化为 unsigned long
    //由此可以得知，原来的程序是在 32位的电脑上测试
    *p = 0;
    while (1)
    {
        sleep(1);
        *p = *p + 1;
        printf("(%d) p: %d\n",getpid(),*p);
    }
    return 0;
}

运行程序的一个实例

运行程序的多个实例

和书本上的结果不同，两个进程并没有表现出相同的地址

threads.c

#include<pthread.h>
#include<stdio.h>
#include<stdlib.h>
volatile int counter = 0;
int loops;
void *worker(void * arg){
    int i;
    for(int i = 0;i < loops;i++){
        counter++;
    }
    return NULL;
}
int main(int argc,char *argv[]){
    if(argc != 2){
        fprintf(stderr,"usage:threads<value>\n");
        exit(1);
    }
    loops = atoi(argv[1]);
    pthread_t p1,p2;
    int ret = pthread_create(&p1,NULL,worker,NULL);
    if(ret == -1){
        perror("pthread_create");
        exit(1);
    }
    ret = pthread_create(&p2,NULL,worker,NULL);
    if(ret == -1){
        perror("pthread_create");
        exit(1);
    }
    pthread_join(p1,NULL);
    pthread_join(p2,NULL);
    printf("Final Value     : %d\n",counter);
    return 0;
}

每次输出得到的结果都不一样。

顺便复习一下 pthread_join()
pthread_join()函数，以阻塞的方式等待thread指定的线程结束。当函数返回时，被等待线程的资源被收回。如果线程已经结束，那么该函数会立即返回。并且thread指定的线程必须是joinable的。

io.c

#include<stdio.h>
#include<stdlib.h>
#include<assert.h>
#include<fcntl.h>
#include<sys/types.h>
#include<sys/stat.h>
#include<unistd.h>
int main(void){
   // int fd = open("/tmp/file",O_WRONLY | O_CREAT | O_TRUNC,S_IRWXU);
   int fd = open("file.txt",O_WRONLY | O_CREAT | O_TRUNC,S_IRWXU);
    assert(fd > -1);
    int rc = write(fd,"hello world\n",13);
    assert(rc == 13);
    close(fd);
    return 0;
}

程序里面的补充知识

 The following symbolic constants are provided for mode:

              S_IRWXU  00700 user (file owner) has read,  write,  and  execute
                       permission

 O_TRUNC
              If  the file already exists and is a regular file and the access
              mode allows writing (i.e., is O_RDWR or  O_WRONLY)  it  will  be
              truncated to length 0.  If the file is a FIFO or terminal device
              file, the O_TRUNC flag is ignored.   Otherwise,  the  effect  of
              O_TRUNC is unspecified.
//好像是如果原来文件存在，其长度就会被截断成 0