进程管理操作

获取进程ID

man pid

#include <sys/types.h>
#include <unistd.h>

pid_t getpid(void);
pid_t getppid(void);

分别是获取当前进程id，和父进程id。

创建子进程

fork

man fork

#include <unistd.h>

pid_t fork(void);

子进程创建失败返回-1，创建成功，在父进程中返回子进程的进程号，在子进程中返回0。

clone

man clone

clone()比fork()功能更强大，可以传入子进程的运行函数，以及设置namespace等。

#include <sched.h>

int clone(int (*fn)(void *), void *child_stack,
          int flags, void *arg, ...
          /* pid_t *ptid, struct user_desc *tls, pid_t *ctid */ );

/* Prototype for the raw system call */

long clone(unsigned long flags, void *child_stack,
          void *ptid, void *ctid,
          struct pt_regs *regs);

上面第一个定义是glibc提供的，封装了原始的clone系统调用，第二个定义是原始的clone系统调用定义。

关键是参数flags，它的bit位有特殊含义，分别是退出时向父进程发送的信号量和下面的标志位（具体说明查阅手册man clone）：

CLONE_CHILD_CLEARTID (since Linux 2.5.49)
CLONE_CHILD_SETTID (since Linux 2.5.49)
CLONE_FILES (since Linux 2.0)
CLONE_FS (since Linux 2.0)
CLONE_IO (since Linux 2.6.25)
CLONE_NEWIPC (since Linux 2.6.19)
CLONE_NEWNET (since Linux 2.6.24)
CLONE_NEWNS (since Linux 2.4.19)
CLONE_NEWPID (since Linux 2.6.24)
CLONE_NEWUTS (since Linux 2.6.19)
CLONE_PARENT (since Linux 2.3.12)
CLONE_PARENT_SETTID (since Linux 2.5.49)
CLONE_PID (obsolete)
CLONE_PTRACE (since Linux 2.2)
CLONE_SETTLS (since Linux 2.5.32)
CLONE_SIGHAND (since Linux 2.0)
CLONE_STOPPED (since Linux 2.6.0-test2)
CLONE_SYSVSEM (since Linux 2.5.10)
CLONE_THREAD (since Linux 2.4.0-test8)
CLONE_UNTRACED (since Linux 2.5.46)
CLONE_VFORK (since Linux 2.2)
CLONE_VM (since Linux 2.0)

例如子进程退出时向父进程发送SIGCHLD信号：

pid = clone(childFunc, stackTop, CLONE_NEWUTS | SIGCHLD, argv[1]);
if (pid == -1)
    errExit("clone");
printf("clone() returned %ld\n", (long) pid);