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os.kill: differences between Windows and Linux

I want to customize a signal handler on windows, and then use os.kill in other processes to notify the signal to execute the corresponding handler. But the result is that the signal still executes the default handler.
I wrote the following test code, the same code, in the window, did not print anything. In Linux, 'hi' is printed.
import os
import signal
def sigint(*args):
print('hi')
signal.signal(signal.SIGINT , sigint)
os.kill(os.getpid(), signal.SIGINT)
Why lead to such different results?

Python Kill all subprocesses if one of them is finished

I have a python code that is running other scripts with multiple instances using subprocess.Popen and wait for them to finish with subprocess.Popen().wait().
Everything works fine, however I want to kill all subprocesses if one of them is terminated. Here is the code that I use to run multiple instances with python subprocess package
import ctypes
import os
import signal
import subprocess
libc = ctypes.CDLL("libc.so.6")
def set_pdeathsig(sig=signal.SIGTERM):
def callable():
return libc.prctl(1, sig)
return callable
if __name__ == "__main__":
procs = []
for i in range((os.cpu_count() * 2) - 1):
proc = subprocess.Popen(['python', "pythonscript_i_need_to_run/"], preexec_fn=set_pdeathsig(signal.SIGTERM))
procs.append(proc)
procs.append(subprocess.Popen(["python", "other_pythonscript_i_need_to_run"], preexec_fn=set_pdeathsig(signal.SIGTERM)))
for proc in procs:
proc.wait()
The set_pdeathsig function is for killing the children if parent is killed. Long story short I need to kill all children if one is killed. How can I do it ?
*** NOTE ***
When I try to kill the parent when one child is dead with
os.kill(os.getppid(), signal.SIGTERM) it doesn't kill the original parent script. Also I tried to kill by group pid but it didn't work as well.

In Unix and Unix-like Operating System has SIGCHLD signal which is send by OS kernel. This signal will be sent to parent process when child process terminated. If you have no handler for this signal, SIGCHLD signal will ignored by default. But if you have a handler function for this signal, you tell the kernel “hey I have a handler function, when child process terminated please trigger this handler function to run”
In your case, you have many child process, if one of them killed or finished its execution(by exit() syscall) kernel will send a SIGCHLD signal to the parent process which is your shared code.
We have a handler for SIGCHLD signal which is chld_handler() function. When one of the child process terminated, SIGCHLD signal will be sent to parent process and chld_handler function will triggered to run by OS kernel. (This named is signal catching)
In this function signal.signal(signal.SIGCHLD,chld_handler) we tell the kernel, “i have handler function for SIGCHLD signal, don’t ignore it when child terminated”. In chld_handler function which is run when SIGCHLD signal was sent, we call signal.signal(signal.SIGCHLD, signal.SIG_IGN) function that we tell the kernel, “hey I have no handler function, ignore the SIGCHLD signal” we do that because we do not need that anymore since we killing other childs with p.terminate() looping the procs.
All code would be like below
import ctypes
import os
import signal
import subprocess
libc = ctypes.CDLL("libc.so.6")
def set_pdeathsig(sig=signal.SIGTERM):
def callable():
return libc.prctl(1, sig)
return callable
def chld_handler(sig, frame):
signal.signal(signal.SIGCHLD, signal.SIG_IGN)
print("one of the childs dead")
for p in procs:
p.terminate()
signal.signal(signal.SIGCHLD,chld_handler)
if __name__ == "__main__":
procs = []
for i in range((os.cpu_count() * 2) - 1):
proc = subprocess.Popen(['python', "pythonscript_i_need_to_run/"], preexec_fn=set_pdeathsig(signal.SIGTERM))
procs.append(proc)
procs.append(subprocess.Popen(["python", "other_pythonscript_i_need_to_run"], preexec_fn=set_pdeathsig(signal.SIGTERM)))
for proc in procs:
proc.wait()
Also there are much more detail about SIGCHLD signal and python signal library and also zombie process, i do not tell all the thing here because there are so many detail, and i am not expert all the deep knowledge now
I hope above informations give you some insight. If you think i am wrong somewhere, please correct me

Signal delivery (in python, that is using user-defined signal.signal() handlers) is sometimes race-prone. It's easy to code a solution that works most of the time, but may yet miss a signal that arrives just before or just after you are prepared to deal with it.
(For reliable delivery as an I/O event, the venerable self-pipe trick may be implemented in python.)
Signal acceptance is another approach, in which you SIG_BLOCK a signal to hold it pending when generated, and then accept it with the signal module's sigwait(), sigwaitinfo(), or sigtimedwait() when you're ready to do so. There's no chance of missing the signal here, but you must remember that basic UNIX signals do not queue up: only one signal of each type will be held pending for acceptance regardless of how many times that signal was generated.
For your problem, that would look something like this, assuming your implementation supported signal.pthread_sigmask():
def main():
signal.pthread_sigmask(signal.SIG_BLOCK, [signal.SIGCHLD])
... launch children ...
signal.sigwait([signal.SIGCHLD])
# OK, at least one child terminated
... terminate other children ...

Gracefully terminating a subprocess in python [duplicate]

I am trying the code pasted below on Windows, but instead of handling signal, it is killing the process.
However, the same code is working in Ubuntu.
import os, sys
import time
import signal
def func(signum, frame):
print 'You raised a SigInt! Signal handler called with signal', signum
signal.signal(signal.SIGINT, func)
while True:
print "Running...",os.getpid()
time.sleep(2)
os.kill(os.getpid(),signal.SIGINT)

Python's os.kill wraps two unrelated APIs on Windows. It calls GenerateConsoleCtrlEvent when the sig parameter is CTRL_C_EVENT or CTRL_BREAK_EVENT. In this case the pid parameter is a process group ID. If the latter call fails, and for all other sig values, it calls OpenProcess and then TerminateProcess. In this case the pid parameter is a process ID, and the sig value is passed as the exit code. Terminating a Windows process is akin to sending SIGKILL to a POSIX process. Generally this should be avoided since it doesn't allow the process to exit cleanly.
Note that the docs for os.kill mistakenly claim that "kill() additionally takes process handles to be killed", which was never true. It calls OpenProcess to get a process handle.
The decision to use WinAPI CTRL_C_EVENT and CTRL_BREAK_EVENT, instead of SIGINT and SIGBREAK, is unfortunate for cross-platform code. It's also not defined what GenerateConsoleCtrlEvent does when passed a process ID that's not a process group ID. Using this function in an API that takes a process ID is dubious at best, and potentially very wrong.
For your particular needs you can write an adapter function that makes os.kill a bit more friendly for cross-platform code. For example:
import os
import sys
import time
import signal
if sys.platform != 'win32':
kill = os.kill
sleep = time.sleep
else:
# adapt the conflated API on Windows.
import threading
sigmap = {signal.SIGINT: signal.CTRL_C_EVENT,
signal.SIGBREAK: signal.CTRL_BREAK_EVENT}
def kill(pid, signum):
if signum in sigmap and pid == os.getpid():
# we don't know if the current process is a
# process group leader, so just broadcast
# to all processes attached to this console.
pid = 0
thread = threading.current_thread()
handler = signal.getsignal(signum)
# work around the synchronization problem when calling
# kill from the main thread.
if (signum in sigmap and
thread.name == 'MainThread' and
callable(handler) and
pid == 0):
event = threading.Event()
def handler_set_event(signum, frame):
event.set()
return handler(signum, frame)
signal.signal(signum, handler_set_event)
try:
os.kill(pid, sigmap[signum])
# busy wait because we can't block in the main
# thread, else the signal handler can't execute.
while not event.is_set():
pass
finally:
signal.signal(signum, handler)
else:
os.kill(pid, sigmap.get(signum, signum))
if sys.version_info[0] > 2:
sleep = time.sleep
else:
import errno
# If the signal handler doesn't raise an exception,
# time.sleep in Python 2 raises an EINTR IOError, but
# Python 3 just resumes the sleep.
def sleep(interval):
'''sleep that ignores EINTR in 2.x on Windows'''
while True:
try:
t = time.time()
time.sleep(interval)
except IOError as e:
if e.errno != errno.EINTR:
raise
interval -= time.time() - t
if interval <= 0:
break
def func(signum, frame):
# note: don't print in a signal handler.
global g_sigint
g_sigint = True
#raise KeyboardInterrupt
signal.signal(signal.SIGINT, func)
g_kill = False
while True:
g_sigint = False
g_kill = not g_kill
print('Running [%d]' % os.getpid())
sleep(2)
if g_kill:
kill(os.getpid(), signal.SIGINT)
if g_sigint:
print('SIGINT')
else:
print('No SIGINT')
Discussion
Windows doesn't implement signals at the system level [*]. Microsoft's C runtime implements the six signals that are required by standard C: SIGINT, SIGABRT, SIGTERM, SIGSEGV, SIGILL, and SIGFPE.
SIGABRT and SIGTERM are implemented just for the current process. You can call the handler via C raise. For example (in Python 3.5):
>>> import signal, ctypes
>>> ucrtbase = ctypes.CDLL('ucrtbase')
>>> c_raise = ucrtbase['raise']
>>> foo = lambda *a: print('foo')
>>> signal.signal(signal.SIGTERM, foo)
<Handlers.SIG_DFL: 0>
>>> c_raise(signal.SIGTERM)
foo
0
SIGTERM is useless.
You also can't do much with SIGABRT using the signal module because the abort function kills the process once the handler returns, which happens immediately when using the signal module's internal handler (it trips a flag for the registered Python callable to be called in the main thread). For Python 3 you can instead use the faulthandler module. Or call the CRT's signal function via ctypes to set a ctypes callback as the handler.
The CRT implements SIGSEGV, SIGILL, and SIGFPE by setting a Windows structured exception handler for the corresponding Windows exceptions:
STATUS_ACCESS_VIOLATION SIGSEGV
STATUS_ILLEGAL_INSTRUCTION SIGILL
STATUS_PRIVILEGED_INSTRUCTION SIGILL
STATUS_FLOAT_DENORMAL_OPERAND SIGFPE
STATUS_FLOAT_DIVIDE_BY_ZERO SIGFPE
STATUS_FLOAT_INEXACT_RESULT SIGFPE
STATUS_FLOAT_INVALID_OPERATION SIGFPE
STATUS_FLOAT_OVERFLOW SIGFPE
STATUS_FLOAT_STACK_CHECK SIGFPE
STATUS_FLOAT_UNDERFLOW SIGFPE
STATUS_FLOAT_MULTIPLE_FAULTS SIGFPE
STATUS_FLOAT_MULTIPLE_TRAPS SIGFPE
The CRT's implementation of these signals is incompatible with Python's signal handling. The exception filter calls the registered handler and then returns EXCEPTION_CONTINUE_EXECUTION. However, Python's handler only trips a flag for the interpreter to call the registered callable sometime later in the main thread. Thus the errant code that triggered the exception will continue to trigger in an endless loop. In Python 3 you can use the faulthandler module for these exception-based signals.
That leaves SIGINT, to which Windows adds the non-standard SIGBREAK. Both console and non-console processes can raise these signals, but only a console process can receive them from another process. The CRT implements this by registering a console control event handler via SetConsoleCtrlHandler.
The console sends a control event by creating a new thread in an attached process that begins executing at CtrlRoutine in kernel32.dll or kernelbase.dll (undocumented). That the handler doesn't execute on the main thread can lead to synchronization problems (e.g. in the REPL or with input). Also, a control event won't interrupt the main thread if it's blocked while waiting on a synchronization object or waiting for synchronous I/O to complete. Care needs to be taken to avoid blocking in the main thread if it should be interruptible by SIGINT. Python 3 attempts to work around this by using a Windows event object, which can also be used in waits that should be interruptible by SIGINT.
When the console sends the process a CTRL_C_EVENT or CTRL_BREAK_EVENT, the CRT's handler calls the registered SIGINT or SIGBREAK handler, respectively. The SIGBREAK handler is also called for the CTRL_CLOSE_EVENT that the console sends when its window is closed. Python defaults to handling SIGINT by rasing a KeyboardInterrupt in the main thread. However, SIGBREAK is initially the default CTRL_BREAK_EVENT handler, which calls ExitProcess(STATUS_CONTROL_C_EXIT).
You can send a control event to all processes attached to the current console via GenerateConsoleCtrlEvent. This can target a subset of processes that belong to a process group, or target group 0 to send the event to all processes attached to the current console.
Process groups aren't a well-documented aspect of the Windows API. There's no public API to query the group of a process, but every process in a Windows session belongs to a process group, even if it's just the wininit.exe group (services session) or winlogon.exe group (interactive session). A new group is created by passing the creation flag CREATE_NEW_PROCESS_GROUP when creating a new process. The group ID is the process ID of the created process. To my knowledge, the console is the only system that uses the process group, and that's just for GenerateConsoleCtrlEvent.
What the console does when the target ID isn't a process group ID is undefined and should not be relied on. If both the process and its parent process are attached to the console, then sending it a control event basically acts like the target is group 0. If the parent process isn't attached to the current console, then GenerateConsoleCtrlEvent fails, and os.kill calls TerminateProcess. Weirdly, if you target the "System" process (PID 4) and its child process smss.exe (session manager), the call succeeds but nothing happens except that the target is mistakenly added to the list of attached processes (i.e. GetConsoleProcessList). It's probably because the parent process is the "Idle" process, which, since it's PID 0, is implicitly accepted as the broadcast PGID. The parent process rule also applies to non-console processes. Targeting a non-console child process does nothing -- except mistakenly corrupt the console process list by adding the unattached process. I hope it's clear that you should only send a control event to either group 0 or to a known process group that you created via CREATE_NEW_PROCESS_GROUP.
Don't rely on being able to send CTRL_C_EVENT to anything but group 0, since it's initially disabled in a new process group. It's not impossible to send this event to a new group, but the target process first has to enable CTRL_C_EVENT by calling SetConsoleCtrlHandler(NULL, FALSE).
CTRL_BREAK_EVENT is all you can depend on since it can't be disabled. Sending this event is a simple way to gracefully kill a child process that was started with CREATE_NEW_PROCESS_GROUP, assuming it has a Windows CTRL_BREAK_EVENT or C SIGBREAK handler. If not, the default handler will terminate the process, setting the exit code to STATUS_CONTROL_C_EXIT. For example:
>>> import os, signal, subprocess
>>> p = subprocess.Popen('python.exe',
... stdin=subprocess.PIPE,
... creationflags=subprocess.CREATE_NEW_PROCESS_GROUP)
>>> os.kill(p.pid, signal.CTRL_BREAK_EVENT)
>>> STATUS_CONTROL_C_EXIT = 0xC000013A
>>> p.wait() == STATUS_CONTROL_C_EXIT
True
Note that CTRL_BREAK_EVENT wasn't sent to the current process, because the example targets the process group of the child process (including all of its child processes that are attached to the console, and so on). If the example had used group 0, the current process would have been killed as well since I didn't define a SIGBREAK handler. Let's try that, but with a handler set:
>>> ctrl_break = lambda *a: print('^BREAK')
>>> signal.signal(signal.SIGBREAK, ctrl_break)
<Handlers.SIG_DFL: 0>
>>> os.kill(0, signal.CTRL_BREAK_EVENT)
^BREAK
[*]
Windows has asynchronous procedure calls (APC) to queue a target function to a thread. See the article Inside NT's Asynchronous Procedure Call for an in-depth analysis of Windows APCs, especially to clarify the role of kernel-mode APCs. You can queue a user-mode APC to a thread via QueueUserAPC. They also get queued by ReadFileEx and WriteFileEx for the I/O completion routine.
A user-mode APC executes when the thread enters an alertable wait (e.g. WaitForSingleObjectEx or SleepEx with bAlertable as TRUE). Kernel-mode APCs, on the other hand, get dispatched immediately (when the IRQL is below APC_LEVEL). They're typically used by the I/O manager to complete asynchronous I/O Request Packets in the context of the thread that issued the request (e.g. copying data from the IRP to a user-mode buffer). See Waits and APCs for a table that shows how APCs affect alertable and non-alertable waits. Note that kernel-mode APCs don't interrupt a wait, but instead are executed internally by the wait routine.
Windows could implement POSIX-like signals using APCs, but in practice it uses other means for the same ends. For example:
Structured Exception Handling, e.g. __try, __except, __finally, __leave, RaiseException, AddVectoredExceptionHandler.
Kernel Dispatcher Objects (i.e. Synchronization Objects), e.g. SetEvent, SetWaitableTimer.
Window Messages, e.g. SendMessage (to a window procedure), PostMessage (to a thread's message queue to be dispatched to a window procedure), PostThreadMessage (to a thread's message queue), WM_CLOSE, WM_TIMER.
Window messages can be sent and posted to all threads that share the calling thread's desktop and that are at the same or lower integrity level. Sending a window message puts it in a system queue to call the window procedure when the thread calls PeekMessage or GetMessage. Posting a message adds it to the thread's message queue, which has a default quota of 10,000 messages. A thread with a message queue should have a message loop to process the queue via GetMessage and DispatchMessage. Threads in a console-only process typically do not have a message queue. However, the console host process, conhost.exe, obviously does. When the close button is clicked, or when the primary process of a console is killed via the task manager or taskkill.exe, a WM_CLOSE message is posted to the message queue of the console window's thread. The console in turns sends a CTRL_CLOSE_EVENT to all of its attached processes. If a process handles the event, it's given 5 seconds to exit gracefully before it's forcefully terminated.

For Python >=3.8, use signal.raise_signal. This directly triggers the signal in the current process, avoiding complications of os.kill interpreting process ID incorrectly.
import os
import time
import signal
def func(signum, frame):
print (f"You raised a SigInt! Signal handler called with signal {signum}")
signal.signal(signal.SIGINT, func)
while True:
print(f"Running...{os.getpid()}")
time.sleep(2)
signal.raise_signal(signal.SIGINT)
Works great!

How to stop Python PyGame program from a thread [duplicate]

How can I exit my entire Python application from one of its threads? sys.exit() only terminates the thread in which it is called, so that is no help.
I would not like to use an os.kill() solution, as this isn't very clean.

Short answer: use os._exit.
Long answer with example:
I yanked and slightly modified a simple threading example from a tutorial on DevShed:
import threading, sys, os
theVar = 1
class MyThread ( threading.Thread ):
def run ( self ):
global theVar
print 'This is thread ' + str ( theVar ) + ' speaking.'
print 'Hello and good bye.'
theVar = theVar + 1
if theVar == 4:
#sys.exit(1)
os._exit(1)
print '(done)'
for x in xrange ( 7 ):
MyThread().start()
If you keep sys.exit(1) commented out, the script will die after the third thread prints out. If you use sys.exit(1) and comment out os._exit(1), the third thread does not print (done), and the program runs through all seven threads.
os._exit "should normally only be used in the child process after a fork()" -- and a separate thread is close enough to that for your purpose. Also note that there are several enumerated values listed right after os._exit in that manual page, and you should prefer those as arguments to os._exit instead of simple numbers like I used in the example above.

If all your threads except the main ones are daemons, the best approach is generally thread.interrupt_main() -- any thread can use it to raise a KeyboardInterrupt in the main thread, which can normally lead to reasonably clean exit from the main thread (including finalizers in the main thread getting called, etc).
Of course, if this results in some non-daemon thread keeping the whole process alive, you need to followup with os._exit as Mark recommends -- but I'd see that as the last resort (kind of like a kill -9;-) because it terminates things quite brusquely (finalizers not run, including try/finally blocks, with blocks, atexit functions, etc).

Using thread.interrupt_main() may not help in some situation. KeyboardInterrupts are often used in command line applications to exit the current command or to clean the input line.
In addition, os._exit will kill the process immediately without running any finally blocks in your code, which may be dangerous (files and connections will not be closed for example).
The solution I've found is to register a signal handler in the main thread that raises a custom exception. Use the background thread to fire the signal.
import signal
import os
import threading
import time
class ExitCommand(Exception):
pass
def signal_handler(signal, frame):
raise ExitCommand()
def thread_job():
time.sleep(5)
os.kill(os.getpid(), signal.SIGUSR1)
signal.signal(signal.SIGUSR1, signal_handler)
threading.Thread(target=thread_job).start() # thread will fire in 5 seconds
try:
while True:
user_input = raw_input('Blocked by raw_input loop ')
# do something with 'user_input'
except ExitCommand:
pass
finally:
print('finally will still run')
Related questions:
Why does sys.exit() not exit when called inside a thread in Python?
Python: How to quit CLI when stuck in blocking raw_input?

The easiest way to exit the whole program is, we should terminate the program by using the process id (pid).
import os
import psutil
current_system_pid = os.getpid()
ThisSystem = psutil.Process(current_system_pid)
ThisSystem.terminate()
To install psutl:- "pip install psutil"

For Linux you can use the kill() command and pass the current process' ID and the SIGINT signal to start the steps to exit the app.
import signal
os.kill(os.getpid(), signal.SIGINT)

Installing signal handler with Python

(there is a follow up to this question here)
I am working on trying to write a Python based Init system for Linux but I'm having an issue getting signals to my Python init script. From the 'man 2 kill' page:
The only signals that can be sent to process ID 1, the init process, are those for which init has explicitly installed signal handlers.
In my Python based Init, I have a test function and a signal handler setup to call that function:
def SigTest(SIG, FRM):
print "Caught SIGHUP!"
signal.signal(signal.SIGHUP, SigTest)
From another TTY (the init script executes sh on another tty) if I send a signal, it is completely ignored and the text is never printed. kill -HUP 1
I found this issue because I wrote a reaping function for my Python init to reap its child processes as they die, but they all just zombied, it took awhile to figure out Python was never getting the SIGCHLD signal. Just to ensure my environment is sane, I wrote a C program to fork and have the child send PID 1 a signal and it did register.
How do I install a signal handler the system will acknowledge if signal.signal(SIG, FUNC) isn't working?
Im going to try using ctypes to register my handler with C code and see if that works, but I rather a pure Python answer if at all possible.
Ideas?
( I'm not a programmer, Im really in over my head here :p )
Test code below...
import os
import sys
import time
import signal
def SigTest(SIG, FRM):
print "SIGINT Caught"
print "forking for ash"
cpid = os.fork()
if cpid == 0:
os.closerange(0, 4)
sys.stdin = open('/dev/tty2', 'r')
sys.stdout = open('/dev/tty2', 'w')
sys.stderr = open('/dev/tty2', 'w')
os.execv('/bin/ash', ('ash',))
print "ash started on tty2"
signal.signal(signal.SIGHUP, SigTest)
while True:
time.sleep(5.0)

Signal handlers mostly work in Python. But there are some problems. One is that your handler won't run until the interpreter re-enters it's bytecode interpreter. if your program is blocked in a C function the signal handler is not called until it returns. You don't show the code where you are waiting. Are you using signal.pause()?
Another is that if you are in a system call you will get an exception after the singal handler returns. You need to wrap all system calls with a retry handler (at least on Linux).
It's interesting that you are writing an init replacement... That's something like a process manager. The proctools code might interest you, since it does handle SIGCHLD.
By the way, this code:
import signal
def SigTest(SIG, FRM):
print "SIGINT Caught"
signal.signal(signal.SIGHUP, SigTest)
while True:
signal.pause()
Does work on my system.