posix_spawn(）:使用posix_scawn(）时的错误处理问题

posix_spawn() : Problem with error handling when using posix_spawn()

本文关键字：posix 错误 处理问题 spawn 使用 scawn      更新时间：2023-10-16

我正在尝试使用posix_spawn((创建一个新的子进程。子进程启动后，调用方进程应继续运行。

TLDR：为什么即使子可执行文件的路径无效(不存在(，posix_spawn((也会返回0(成功(？如何正确检测这种情况下的错误，以及posix_spown实际失败但返回成功的任何其他情况？

我尝试了以下代码。

/* The CALLER process*/
int main(int argc, char *argv) {
int status, pid;
printf("CALLER - Startn");
char *args[] = {"/home/<user>/child_exec", NULL};
status = posix_spawn(&pid, args[0], NULL, NULL, args, environ);
printf("Status: %d; PID: %dn", status, pid);
printf("CALLER - Endn");
return 0;
}

/* The CHILD process */
int main() {
printf("From CHILDn");
return 0;
}

当我运行带有正确子可执行文件路径的调用程序时，它会按预期运行。posix_spown的状态为0，并且将打印来自子进程的字符串。

CALLER - Start
Status: 0; PID: 5110
CALLER - End
From CHILD

现在，当我使用无效的子可执行路径(例如/home/user/child_exec123(运行同一程序时，即使子进程尚未执行，它仍然返回状态0。

CALLER - Start
Status: 0; PID: 5251
CALLER - End

对于这种不存在子路径的情况，我可以在调用posix_spawn((之前检查文件是否存在。但是，如果还有其他类似的错误，posix_spawn((实际上失败了，但返回0，该怎么办？如何查找是否存在错误？

来自手册页(特别是第二段(：

RETURN VALUE
Upon successful completion, posix_spawn() and posix_spawnp() place  the
PID  of  the  child process in pid, and return 0.  If there is an error
before or during the fork(2), then no child is created, the contents of
*pid are unspecified, and these functions return an error number as de‐
scribed below.
Even when these functions return a success status,  the  child  process
may still fail for a plethora of reasons related to its pre-exec() ini‐
tialization.  In addition, the exec(3)  may  fail.   In  all  of  these
cases, the child process will exit with the exit value of 127.

您需要使用其中一个wait*函数来检查子进程的结果。无论如何，这都是个好主意，否则你会有一个僵尸。

posix_spawn在子进程启动之前返回，在该进程中将检测到不正确的路径。所以，在启动子进程的过程中，您只能通过它的退出值来检查任何错误。

如文件所述：

返回值

Upon successful completion, posix_spawn() and posix_spawnp() place
the PID of the child process in pid, and return 0.  If there is an
error during the fork() step, then no child is created, the contents
of *pid are unspecified, and these functions return an error number
as described below.
Even when these functions return a success status, the child process
may still fail for a plethora of reasons related to its pre-exec()
initialization.  In addition, the exec(3) may fail.  In all of these
cases, the child process will exit with the exit value of 127.

错误

The posix_spawn() and posix_spawnp() functions fail only in the case
where the underlying fork(2), vfork(2) or clone(2) call fails;  in
these cases, these functions return an error number, which will be
one of the errors described for fork(2), vfork(2) or clone(2).
In addition, these functions fail if:
ENOSYS Function not supported on this system.
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