尽管我在 python ctypes 中设置了信号处理程序，但不会调用它

问题描述

我已经尝试使用 sigaction 和 ctypes 设置信号处理程序.(我知道它可以在 python 中使用信号模块，但我想尝试学习.)

当我将 SIGTERM 发送到此进程，但它不调用我设置的处理程序时，只打印已终止".为什么它不调用处理程序?

我使用 Ubuntu 19.10 和 Python 3.7.5 x64.

import ctypes从 ctypes 导入 *从 ctypes.util 导入 *从 os 导入 getpid类 sigset_t(结构):__字段__ = [("__val", c_ulong*16)]类 sigval_t(联合):__字段__ = [("sival_int", c_int),("sival_ptr", c_void_p)]类 siginfo_t(结构):__字段__ = [("si_signo", c_int),("si_errno", c_int),("si_code", c_int),("si_trapno", c_int),("si_pid", c_uint),("si_status", c_int),("si_utime", c_long),("si_stime", c_long),("si_value", sigval_t),("si_int", c_int),("si_ptr", c_void_p),("si_overrun", c_int),("si_timerid", c_int),("si_addr", c_void_p),("si_band", c_long),("si_fd", c_int),("si_addr_lsb", c_short),("si_call_addr", c_void_p),("si_syscall", c_int),(si_arch"，c_uint)]sa_handler_functype = CFUNCTYPE(无，c_int)sigaction_functype = CFUNCTYPE(无，c_int，siginfo_t，c_void_p)类SIGACTION(结构):__字段__ = [(sa_handler"，sa_handler_functype)，("sa_sigaction", sigaction_functype),(sa_mask"，sigset_t)，("sa_flags", c_int),]def p(sig): # 信号处理函数libc.puts("再见")libc_path = find_library("c")libc = CDLL(libc_path)libc.sigaction.restype = c_intlibc.sigaction.argtypes = [c_int, POINTER(SIGACTION), POINTER(SIGACTION)]行为 = SIGACTION(sa_handler=sa_handler_functype(p))打印(行为)res = libc.sigaction(15, act, None)打印(资源)print("pid:", getpid()) # 显示pidwhile True: # 等待直到收到 sigterm 信号经过

解决方案

Listing [Python 3.Docs]: ctypes - Python 的外部函数库.

代码有问题:

• ctypes.Structure 后代需要定义_fields_(而不是 __fields__).相应地改变了结构
• 将 struct sigaction *(指针)作为参数传递给 sigaction
• 根据 /usr/include/bits 中文件的内容修改结构定义(在我的 Ubtu 16 x64 VM 上)
• 为任何使用的函数(puts)定义了argtypes和restype.检查 [SO]:C 函数调用从 Python 通过 ctypes 返回不正确的值(@CristiFati 的回答) 了解更多详情
• 其他(次要)变化

code00.py:

#!/usr/bin/env python3导入系统导入操作系统导入时间从 ctypes 导入结构、联合、指针、CFUNCTYPE、CDLL、byref、sizeof、\c_short、c_int、c_uint、c_long、c_ulong、c_char_p、c_void_pSIGTERM = 15类 sigset_t(结构):_字段_ = [("__val", c_ulong * (1024//(8 * sizeof (c_long)))),]'''类 sigval_t(联合):_字段_ = [("sival_int", c_int),("sival_ptr", c_void_p),]类 siginfo_t(结构):_字段_ = [("si_signo", c_int),("si_errno", c_int),("si_code", c_int),("_pad", c_int * 29),]sa_sigaction_functype = CFUNCTYPE(无，c_int，指针(siginfo_t)，c_void_p)'''sa_handler_functype = CFUNCTYPE(无，c_int，use_errno=True)类SIGACTION(结构):_字段_ = [(sa_handler"，sa_handler_functype)，(sa_mask"，sigset_t)，("sa_flags", c_int),("sa_restorer", c_void_p),]libc = CDLL(无)def sighhandler(sig): # 信号处理函数libc.puts.argtypes = [c_char_p]libc.puts.restype = c_intlibc.puts("自定义信号处理程序调用信号{0:d}".format(sig).encode())def main(*argv):libc.sigaction.argtypes = [c_int, POINTER(SIGACTION), POINTER(SIGACTION)]libc.sigaction.restype = c_int信号编号 = SIGTERM行为 = SIGACTION(sa_handler=sa_handler_functype(sighandler))#打印(行为)res = libc.sigaction(signal_number, byref(act), None)print("sigaction 结果:{0:d}".format(res))打印(PId {0:d}等待SIG {1:d}...".格式(os.getpid()，signal_number))而 1:时间.睡眠(0.1)如果 __name__ == "__main__":print("Python {0:s} {1:d}bit on {2:s}\n".format(" ".join(item.strip() for item in sys.version.split("\n")), 64 如果 sys.maxsize > 0x100000000 否则 32, sys.platform))main(*sys.argv[1:])打印(\n完成.")

输出(程序运行时，发送两次SIGTERM，然后从另一个终端发送SIGKILL):

[cfati@cfati-ubtu16x64-0:~/Work/Dev/StackOverflow/q059521251]>用户名 -mx86_64[cfati@cfati-ubtu16x64-0:~/Work/Dev/StackOverflow/q059521251]>cat/etc/lsb-release |语法描述DISTRIB_DESCRIPTION="Ubuntu 16.04.6 LTS"[cfati@cfati-ubtu16x64-0:~/Work/Dev/StackOverflow/q059521251]>python3 code00.pyPython 3.5.2(默认，2019 年 10 月 8 日，13:06:37)[GCC 5.4.0 20160609] 64 位 Linux签名结果:0PId 20050 等待 SIG 15...自定义信号处理程序调用信号 15自定义信号处理程序调用信号 15被杀

I have tried set signal handler with sigaction and ctypes. (I know it is able to do with signal module in python, but I want to try it for learn.)

When I sent SIGTERM to this process, but it does not call handler that I set, only print "Terminated".Why it does not invoke the handler?

I using Ubuntu 19.10 and Python 3.7.5 x64.

import ctypes
from ctypes import *
from ctypes.util import *
from os import getpid


class sigset_t(Structure):
    __fields__ = [
        ("__val",               c_ulong*16)
    ]

class sigval_t(Union):
    __fields__ = [
        ("sival_int",           c_int),
        ("sival_ptr",           c_void_p)
    ]



class siginfo_t(Structure):
    __fields__ = [
        ("si_signo",            c_int),
        ("si_errno",            c_int),
        ("si_code",             c_int),
        ("si_trapno",           c_int),
        ("si_pid",              c_uint),
        ("si_status",           c_int),
        ("si_utime",            c_long),
        ("si_stime",            c_long),
        ("si_value",            sigval_t),
        ("si_int",              c_int),
        ("si_ptr",              c_void_p),
        ("si_overrun",          c_int),
        ("si_timerid",          c_int),
        ("si_addr",             c_void_p),
        ("si_band",             c_long),
        ("si_fd",               c_int),
        ("si_addr_lsb",         c_short),
        ("si_call_addr",        c_void_p),
        ("si_syscall",          c_int),
        ("si_arch",             c_uint)

    ]

sa_handler_functype = CFUNCTYPE(None, c_int)
sigaction_functype = CFUNCTYPE(None, c_int, siginfo_t, c_void_p)


class SIGACTION(Structure):
    __fields__ = [
        ("sa_handler",          sa_handler_functype),
        ("sa_sigaction",        sigaction_functype),
        ("sa_mask",             sigset_t),
        ("sa_flags",            c_int),

    ]


def p(sig): # signal handler function
    libc.puts("bye")

libc_path = find_library("c")
libc = CDLL(libc_path)

libc.sigaction.restype = c_int
libc.sigaction.argtypes = [c_int, POINTER(SIGACTION), POINTER(SIGACTION)]

act = SIGACTION(sa_handler=sa_handler_functype(p))
print(act)
res = libc.sigaction(15, act, None)
print(res)
print("pid:", getpid()) # show pid
while True: # wait until receive sigterm signal
    pass

解决方案

Listing [Python 3.Docs]: ctypes - A foreign function library for Python.

There are some problems with the code:

• ctypes.Structure descendants need to define _fields_ (and not __fields__). Changed the structures accordingly
• Passed a struct sigaction * (pointer) as argument to sigaction
• Modified structures definitions based on contents from files in /usr/include/bits (on my Ubtu 16 x64 VM)
• Defined argtypes and restype for any used function (puts). Check [SO]: C function called from Python via ctypes returns incorrect value (@CristiFati's answer) for more details
• Other (minor) changes

code00.py:

#!/usr/bin/env python3

import sys
import os
import time
from ctypes import Structure, Union, POINTER, CFUNCTYPE, CDLL, byref, sizeof, \
    c_short, c_int, c_uint, c_long, c_ulong, c_char_p, c_void_p


SIGTERM = 15


class sigset_t(Structure):
    _fields_ = [
        ("__val", c_ulong * (1024 // (8 * sizeof (c_long)))),
    ]


'''
class sigval_t(Union):
    _fields_ = [
        ("sival_int", c_int),
        ("sival_ptr", c_void_p),
    ]


class siginfo_t(Structure):
    _fields_ = [
        ("si_signo", c_int),
        ("si_errno", c_int),
        ("si_code", c_int),
        ("_pad", c_int * 29),
    ]


sa_sigaction_functype = CFUNCTYPE(None, c_int, POINTER(siginfo_t), c_void_p)
'''
sa_handler_functype = CFUNCTYPE(None, c_int, use_errno=True)


class SIGACTION(Structure):
    _fields_ = [
        ("sa_handler", sa_handler_functype),
        ("sa_mask", sigset_t),
        ("sa_flags", c_int),
        ("sa_restorer", c_void_p),
    ]


libc = CDLL(None)


def sighandler(sig):  # Signal handler function
    libc.puts.argtypes = [c_char_p]
    libc.puts.restype = c_int
    libc.puts("Custom signal handler called for signal {0:d}".format(sig).encode())


def main(*argv):

    libc.sigaction.argtypes = [c_int, POINTER(SIGACTION), POINTER(SIGACTION)]
    libc.sigaction.restype = c_int

    signal_number = SIGTERM
    act = SIGACTION(sa_handler=sa_handler_functype(sighandler))
    #print(act)

    res = libc.sigaction(signal_number, byref(act), None)
    print("sigaction result: {0:d}".format(res))
    print("PId {0:d} waiting for SIG {1:d}...".format(os.getpid(), signal_number))

    while 1:
        time.sleep(0.1)


if __name__ == "__main__":
    print("Python {0:s} {1:d}bit on {2:s}\n".format(" ".join(item.strip() for item in sys.version.split("\n")), 64 if sys.maxsize > 0x100000000 else 32, sys.platform))
    main(*sys.argv[1:])
    print("\nDone.")

Output (while program running, sent SIGTERM twice then SIGKILL from another terminal):

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