Python中的事件驱动系统调用

Question

我正在尝试通过系统调用或子流程来实现事件驱动的流程。基本上，我想启动一个非阻塞系统命令，并且在该系统调用完成后，我希望一个函数被调用。这样一来，我可以启动GUI进度栏，启动系统命令并使进度栏继续运行，并在系统调用结束时停止进度栏。

我绝对不希望做的是生成一个进程，获取其进程ID，并在while循环中继续检查该进程的完成情况。

下面只是一个我如何想象它应该工作的示例（所有这些都在一个类中）

def launchTool(self):

    self.progressbar.config(mode = 'indeterminate')
    self.progressbar.start(20)
    self.launchButton.config(state = 'disabled')
    self.configCombobox.config(state = 'disabled')

    ##  here the "onCompletion" is a pointer to a function
    call("/usr/bin/make psf2_dcf", shell=True, onCompletion = self.toolCompleted)


def onCompletion(self):

    print('DONE running Tool')

    self.progressbar.stop()
    self.launchButton.config(state = 'normal')
    self.configCombobox.config(state = 'normal')

Answer 1

为了避免轮询子进程的状态，可以SIGCHLD在Unix上使用signal。要将其与tkinter的事件循环结合使用，可以使用self-
pipe技巧
。它还解决了可能的tkinter
+信号问题，
而无需定期唤醒事件循环。

#!/usr/bin/env python3
import logging
import os
import signal
import subprocess
import tkinter

info = logging.getLogger(__name__).info

def on_signal(pipe, mask, count=[0]):
    try:
        signals = os.read(pipe, 512)
    except BlockingIOError:
        return # signals have been already dealt with

    # from asyncio/unix_events.py
    #+start
    # Because of signal coalescing, we must keep calling waitpid() as
    # long as we're able to reap a child.
    while True:
        try:
            pid, status = os.waitpid(-1, os.WNOHANG)
        except ChildProcessError:
            info('No more child processes exist.')
            return
        else:
            if pid == 0:
                info('A child process is still alive. signals=%r%s',
                     signals, ' SIGCHLD'*(any(signum == signal.SIGCHLD
                                              for signum in signals)))
                return
            #+end
            # you could call your callback here
            info('{pid} child exited with status {status}'.format(**vars()))
            count[0] += 1
            if count[0] == 2:
                root.destroy() # exit GUI


logging.basicConfig(format="%(asctime)-15s %(message)s", datefmt='%F %T',
                    level=logging.INFO)
root = tkinter.Tk()
root.withdraw() # hide GUI

r, w = os.pipe2(os.O_NONBLOCK | os.O_CLOEXEC) 
signal.set_wakeup_fd(w) 
root.createfilehandler(r, tkinter.READABLE, on_signal)
signal.signal(signal.SIGCHLD, lambda signum, frame: None) # enable SIGCHLD
signal.siginterrupt(signal.SIGCHLD, False) # restart interrupted syscalls automatically
info('run children')
p = subprocess.Popen('sleep 4', shell=True)
subprocess.Popen('sleep 1', shell=True)
root.after(2000, p.send_signal, signal.SIGSTOP) # show that SIGCHLD may be delivered
root.after(3000, p.send_signal, signal.SIGCONT) # while the child is still alive
root.after(5000, lambda: p.poll() is None and p.kill()) # kill it
root.mainloop()
info('done')

输出量

2015-05-20 23:39:50 run children
2015-05-20 23:39:51 16991 child exited with status 0
2015-05-20 23:39:51 A child process is still alive. signals=b'\x11' SIGCHLD
2015-05-20 23:39:52 A child process is still alive. signals=b'\x11' SIGCHLD
2015-05-20 23:39:53 A child process is still alive. signals=b'\x11' SIGCHLD
2015-05-20 23:39:54 16989 child exited with status 0
2015-05-20 23:39:54 No more child processes exist.
2015-05-20 23:39:54 done