waitpid的waitstatus 含义源码解读

当我们在调用pid_t waitpid(pid_t pid, int *stat_loc, int options)时，其中第二个参数stat_loc会提供子进程退出的详细信息，为此posix还提供了一组宏来解析这个status.

在\glibc\bits\waitstatus.h

/* If WIFEXITED(STATUS), the low-order 8 bits of the status.  */

#define  __WEXITSTATUS(status)   (((status) & 0xff00) >> 8)

/* If WIFSIGNALED(STATUS), the terminating signal.  */

#define  __WTERMSIG(status)   ((status) & 0x7f)

/* If WIFSTOPPED(STATUS), the signal that stopped the child.  */

#define  __WSTOPSIG(status)   __WEXITSTATUS(status)

/* Nonzero if STATUS indicates normal termination.  */

#define  __WIFEXITED(status)  (__WTERMSIG(status) == 0)

/* Nonzero if STATUS indicates termination by a signal.  */

#define __WIFSIGNALED(status) \

  (((signed char) (((status) & 0x7f) + 1) >> 1) > 0)

/* Nonzero if STATUS indicates the child is stopped.  */

#define  __WIFSTOPPED(status) (((status) & 0xff) == 0x7f)

/* Nonzero if STATUS indicates the child continued after a stop.  We only

   define this if <bits/waitflags.h> provides the WCONTINUED flag bit.  */

#ifdef WCONTINUED

# define __WIFCONTINUED(status)  ((status) == __W_CONTINUED)

#endif

/* Nonzero if STATUS indicates the child dumped core.  */

#define  __WCOREDUMP(status)  ((status) & __WCOREFLAG)

/* Macros for constructing status values.  */

#define  __W_EXITCODE(ret, sig)  ((ret) << 8 | (sig))

#define  __W_STOPCODE(sig) ((sig) << 8 | 0x7f)

#define __W_CONTINUED      0xffff

#define  __WCOREFLAG    0x80

我们重点看一下#define  __W_EXITCODE(ret, sig)  ((ret) << 8 | (sig))，其中：

ret是exit code，就是子进程在退出时，如果有调用exit()时，产生的exitcode. 比如子进程显示调用了exit(1)，那么exitcode就是1。

sig是signal，比如SIGTERM，这时可以认为子进程是被动kill掉的，所以需要记录此时的SIGNAL。

示例：

pclose return  30720 = 0x7800, 0x78 = 120, 

sys — System-specific parameters and functions — Python 3.13.3 documentation

Changed in version 3.6: If an error occurs in the cleanup after the Python interpreter has caught SystemExit (such as an error flushing buffered data in the standard streams), the exit status is changed to 120.