进程 (一).fork（2）

/* Clone the calling process, creating an exact copy.
   Return -1 for errors, 0 to the new process,
   and the process ID of the new process to the old process.  */
extern __pid_t fork (void) __THROW;
/* Make the process sleep for SECONDS seconds, or until a signal arrives
   and is not ignored.  The function returns the number of seconds less
   than SECONDS which it actually slept (thus zero if it slept the full time).
   If a signal handler does a `longjmp' or modifies the handling of the
   SIGALRM signal while inside `sleep' call, the handling of the SIGALRM
   signal afterwards is undefined.  There is no return value to indicate
   error, but if `sleep' returns SECONDS, it probably didn't work.

   This function is a cancellation point and therefore not marked with
   __THROW.  */
extern unsigned int sleep (unsigned int __seconds);
/* Get the process ID of the calling process.  */
extern __pid_t getpid (void) __THROW;

/* Get the process ID of the calling process's parent.  */
extern __pid_t getppid (void) __THROW;

/* Clone the calling process, creating an exact copy.
   Return -1 for errors, 0 to the new process,
   and the process ID of the new process to the old process.  */
extern __pid_t fork (void) __THROW;
/* Clone the calling process, but without copying the whole address space.
   The calling process is suspended until the new process exits or is
   replaced by a call to `execve'.  Return -1 for errors, 0 to the new process,
   and the process ID of the new process to the old process.  */
extern __pid_t vfork (void) __THROW;

/* Wait for a child to die.  When one does, put its status in *STAT_LOC
   and return its process ID.  For errors, return (pid_t) -1.

   This function is a cancellation point and therefore not marked with
   __THROW.  */
extern __pid_t wait (__WAIT_STATUS __stat_loc);
/* Wait for a child matching PID to die.
   If PID is greater than 0, match any process whose process ID is PID.
   If PID is (pid_t) -1, match any process.
   If PID is (pid_t) 0, match any process with the
   same process group as the current process.
   If PID is less than -1, match any process whose
   process group is the absolute value of PID.
   If the WNOHANG bit is set in OPTIONS, and that child
   is not already dead, return (pid_t) 0.  If successful,
   return PID and store the dead child's status in STAT_LOC.
   Return (pid_t) -1 for errors.  If the WUNTRACED bit is
   set in OPTIONS, return status for stopped children; otherwise don't.

   This function is a cancellation point and therefore not marked with
   __THROW.  */
extern __pid_t waitpid (__pid_t __pid, int *__stat_loc, int __options);

/* Define the macros <sys/wait.h> also would define this way.  */
# define WEXITSTATUS(status)    __WEXITSTATUS (__WAIT_INT (status))
# define WTERMSIG(status)       __WTERMSIG (__WAIT_INT (status))
# define WSTOPSIG(status)       __WSTOPSIG (__WAIT_INT (status))
# define WIFEXITED(status)      __WIFEXITED (__WAIT_INT (status))
# define WIFSIGNALED(status)    __WIFSIGNALED (__WAIT_INT (status))
# define WIFSTOPPED(status)     __WIFSTOPPED (__WAIT_INT (status))

#ifndef _LINUX_WAIT_H
#define _LINUX_WAIT_H

#define WNOHANG         0x00000001
#define WUNTRACED       0x00000002
#define WSTOPPED        WUNTRACED
#define WEXITED         0x00000004
#define WCONTINUED      0x00000008
#define WNOWAIT         0x01000000      /* Don't reap, just poll status.  */

#define __WNOTHREAD     0x20000000      /* Don't wait on children of other threads in this group */
#define __WALL          0x40000000      /* Wait on all children, regardless of type */
#define __WCLONE        0x80000000      /* Wait only on non-SIGCHLD children */

/* First argument to waitid: */
#define P_ALL           0
#define P_PID           1
#define P_PGID          2


#endif