我想分叉一个进程并等待父进程退出,然后再对子进行操作。
答案 0 :(得分:6)
天真的方式就是这样一个繁忙的循环:
# BAD WAY!
pid = os.fork()
if pid == 0:
while True:
if os.path.isdir("/proc/%s" % pid):
break
time.sleep(0.1)
# Parent is dead there.
但这很容易受到PID重用问题的影响。如果在父项退出并获得其PID之后立即创建了另一个进程,则该子进程将永远不会退出。
另一种方法是在特定文件上使用flock()
。但它不起作用,因为孩子与父母共享相同的锁。
这样做的一个万无一失的方法是使用一个特殊技巧:在父级中创建一个管道,在孩子中,你只需等到你得到一个EOF。
# Good way
read_fd, write_fd = os.pipe()
pid = os.fork()
if pid > 0:
# Close the read pipe, so that only the child is the reader.
os.close(read_fd)
# It is important to voluntarily leak write_fd there,
# so that the kernel will close it for the parent process
# when it will exit, triggering our trick.
elif pid == 0:
# Daemon ourselves first.
os.setsid()
for fd in {0, 1, 2}:
os.close(fd)
# Close the write pipe so that the parent is the only writer.
# This will make sure we then get an EOF when the only writer exits.
os.close(write_fd)
# Now, we're waiting on the read pipe for an EOF.
# PS: the assert is not necessary in production...
assert os.read(read_fd, 1) == ""
os.close(read_fd)
# At this point, the parent is dead.