# > cat slow.py
import threading
import subprocess
import time

def _open(cmd, expect):

    t0 = time.time()
    proc = subprocess.Popen(
            cmd,
            shell=True,
            # # without this line, some Popen does not return at once as expected
            # close_fds=True,
            stderr=subprocess.PIPE,
            stdout=subprocess.PIPE)

    spent = time.time() - t0
    if spent > expect:
        print cmd + ' spent: ' + str(spent)

    proc.wait()


for ii in range(100):
    ths = [
            threading.Thread(target=_open, args=('echo 1', 0.01)),
            threading.Thread(target=_open, args=('sleep 0.03', 0.05)),
    ]

    for th in ths:
        th.start()

    for th in ths:
        th.join()

# > python2 slow.py
# echo 1 spent: 0.0381829738617
# echo 1 spent: 0.041118144989
# echo 1 spent: 0.0417079925537
# echo 1 spent: 0.0421600341797
# echo 1 spent: 0.039479970932
# ...

proc = subprocess.Popen(
        cmd,
        close_fds=True, # here
        ...
        )

def pipe_cloexec(self):
    # 1) 创建pipe用于父子进程通信...
    r, w = os.pipe()
    self._set_cloexec_flag(r)
    self._set_cloexec_flag(w)
    return r, w

def _execute_child(self, args, executable, preexec_fn, close_fds,
                   cwd, env, universal_newlines,
                   startupinfo, creationflags, shell, to_close,
                   p2cread, p2cwrite,
                   c2pread, c2pwrite,
                   errread, errwrite):
    # 1) 创建pipe用于父子进程通信...
    errpipe_read, errpipe_write = self.pipe_cloexec()
    try:
        try:
            # 2) 3)
            self.pid = os.fork()
            if self.pid == 0:
                # 子进程流程
                try:
                    # 5) 子进程关闭读的pipe: 不需要接受父进程的消息
                    os.close(errpipe_read)

                    # 如果需要, 子进程关闭所有打开的文件描述符.
                    # 只留下用于告之父进程错误的pipe
                    if close_fds:
                        self._close_fds(but=errpipe_write)

                    # 7) 子进程加载程序
                    os.execvp(executable, args)

                except:
                    exc_type, exc_value, tb = sys.exc_info()
                    exc_lines = traceback.format_exception(exc_type,
                                                           exc_value,
                                                           tb)
                    exc_value.child_traceback = ''.join(exc_lines)

                    # 通过pipe通知父进程错误信息
                    os.write(errpipe_write, pickle.dumps(exc_value))

                # 子进程如果出错, 直接退出. 退出会关闭所有pipe
                os._exit(255)

            # 以下是父进程的流程
        finally:
            # 4) 父进程不需要通知子进程错误消息, 直接关闭pipe的写入端.
            os.close(errpipe_write)

        # 6) 父进程阻塞的读取子进程发来的错误消息.
        data = _eintr_retry_call(os.read, errpipe_read, 1048576)
    finally:
        # 无论成功与否, 父进程不再需要从子进程读取任何消息了, 关闭pipe的读取端.
        os.close(errpipe_read)

    if data != "":
        # 父进程的错误处理...
    # 8) 9)