> For the complete documentation index, see [llms.txt](https://vernon2gb.gitbook.io/notes/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://vernon2gb.gitbook.io/notes/process_thread_scheduler/scheduler01.md).

# scheduler01

## 1. linux进程周期

就绪、运行、睡眠、停止、僵死

## 2. task\_struct

```c
struct task_struct {
    ...
    pid_t pid;
    struct mm_struct *mm;
    struct fs_struct *fs;
    struct files_struct *files;
    ...
};

struct mm_struct {
    ...
    struct vm_area_struct * mmap;
    pgd_t * pgd;
    ...
};

struct fs_struct {
    ...
    struct path root, pwd;
    ...
};

struct files_struct {
    ...
    struct fdtable fdtab;
    struct file * fd_array[NR_OPEN_DEFAULT];
    ...
};
```

task\_struct形成 链表、树、哈希 来管理

## 2. 查看目前系统支持最多pid数量

```bash
$ cat /proc/sys/kernel/pid_max
32768
```

## 3. 内存泄漏

僵死进程，资源已经释放，无内存泄漏，只存下 task\_struct 供父进程查死亡原因

进程运行中，运行越久，内存消耗越多，即 发生内存泄漏

## 4. 停止/恢复进程与作业控制  cpulimit

ctrl + z : 暂停执行进程

fg/bg : 恢复进程执行

```bash
$ cpulimit -l 20 -p 10111
```

限制pid为10111进程的cpu使用率不超过20%

## 5. fork

`$ vim fork1.c`

```c
main()
{
    fork();
    printf("hello\n");
    fork();    
    printf("hello\n");
    while(1);
}
```

`$ vim fork2.c`

```c
#include <stdio.h>
#include <sys/wait.h>
#include <stdlib.h>
#include <unistd.h>

int main(void)
{
    pid_t pid,wait_pid;
    int status;

    pid = fork();

    if (pid==-1) {
        perror("Cannot create new process");
        exit(1);
    } else if (pid==0) {
        printf("a\n");
    } else {
        printf("b\n");
    }

    printf("c\n");
    while(1);
}
```

`$ vim life_period.c`

```c
#include <stdio.h>
#include <sys/wait.h>
#include <stdlib.h>
#include <unistd.h>

int main(void)
{
    pid_t pid,wait_pid;
    int status;

    pid = fork();

    if (pid==-1)    {
        perror("Cannot create new process");
        exit(1);
    } else if (pid==0) {
        printf("child process id: %ld\n", (long) getpid());
        pause();
        _exit(0);
    } else {

#if 0 /* define 1 to make child process always a zomie */
        printf("ppid:%d\n", getpid());
        while(1);
#endif
        do {
            wait_pid=waitpid(pid, &status, WUNTRACED | WCONTINUED);

            if (wait_pid == -1) {
                perror("cannot using waitpid function");
                exit(1);
            }

            if (WIFEXITED(status))
                printf("child process exites, status=%d\n", WEXITSTATUS(status));

            if(WIFSIGNALED(status))
                printf("child process is killed by signal %d\n", WTERMSIG(status));

            if (WIFSTOPPED(status))
                printf("child process is stopped by signal %d\n", WSTOPSIG(status));

            if (WIFCONTINUED(status))
                printf("child process resume running....\n");

        } while (!WIFEXITED(status) && !WIFSIGNALED(status));

        exit(0);
}
```