Re: Calling pselect/ppoll/epoll_pwait
On 12/2/22 14:00, Ian Pilcher wrote: Does Python provide any way to call the "p" variants of the I/O multiplexing functions? Just to close this out ... As others suggested, there's no easy way to call the "p" variants of the I/O multiplexing functions, but this can be worked around by "mapping" signals to file descriptors. There are a few ways to accomplish this. 1. Use a Linux signalfd. There's at least one library out there that provides signalfd support to Python. 2. Use signal.set_wakeup_fd()[1]. I didn't really explore this, as it appears that there isn't any way to filter the signals that will be reported. 3. Roll your own. This turned out to be really simple for my use case, which is simply to set an exit flag and wake my program up if it receives SIGINT or SIGTERM. _sel = selectors.DefaultSelector() _exit_flag = False _sig_pipe_r, _sig_pipe_w = os.pipe2(os.O_NONBLOCK | os.O_CLOEXEC) def _sig_handler(signum, frame): global _exit_flag _exit_flag = True os.write(_sig_pipe_w, b'\x00') _sel.register(_sig_pipe_r, selectors.EVENT_READ) # register other file descriptors of interest signal.signal(signal.SIGINT, _sig_handler) signal.signal(signal.SIGTERM, _sig_handler) while not _exit_flag: ready = _sel.select() # handle other file descriptors [1] https://docs.python.org/3/library/signal.html#signal.set_wakeup_fd -- Google Where SkyNet meets Idiocracy -- https://mail.python.org/mailman/listinfo/python-list
Re: Calling pselect/ppoll/epoll_pwait
On 3 Dec 2022, at 13:13, Weatherby,Gerard wrote: Signalfd and select could probably be made to work if one codes around the race conditions pselect is provided to avoid. I’m not sure if using the GIL (for CPython) is sufficient or if a dedicated concurrency control (e.g. lock, mutex, semaphore) is necessary. An alternative is to call the C library function via a wrapper. I had need to use setfsuid on a project a couple of years ago and found this example: [1]https://gist.github.com/atdt/ebafa299e843a767139b I read this on SO when researching your question. Search for epoll and signal. (I would post the link but ipad turns the link into an image…) I assume that the lack of pepoll means you can use epoll and signalfd without race conditions. The trick seems to be setting the signal to ignore. Barry From: Python-list on behalf of Barry Date: Friday, December 2, 2022 at 7:02 PM To: Ian Pilcher Cc: python-list@python.org Subject: Re: Calling pselect/ppoll/epoll_pwait *** Attention: This is an external email. Use caution responding, opening attachments or clicking on links. *** > On 2 Dec 2022, at 20:03, Ian Pilcher wrote: > > Does Python provide any way to call the "p" variants of the I/O > multiplexing functions? > > Looking at the documentation of the select[1] and selectors[2] modules, > it appears that they expose only the "non-p" variants. > > [1] [2]https://urldefense.com/v3/__https://docs.python.org/3/library/select.html__;!!Cn_UX_p3!hClFFo4XdiwQAhHxDbHA5zFr490Of9uheHSf84V9cREMHyw1kX-baG5HzXWMt-hFLP30q6DpSUb2G_OD5qBjeA$ > [2] [3]https://urldefense.com/v3/__https://docs.python.org/3/library/selectors.html__;!!Cn_UX_p3!hClFFo4XdiwQAhHxDbHA5zFr490Of9uheHSf84V9cREMHyw1kX-baG5HzXWMt-hFLP30q6DpSUb2G_MwNjgO8A$ Can you use signalfd and select/poll/epoll? Barry > > -- > > Google Where SkyNet meets Idiocracy > > -- > [4]https://urldefense.com/v3/__https://mail.python.org/mailman/listinfo/python-list__;!!Cn_UX_p3!hClFFo4XdiwQAhHxDbHA5zFr490Of9uheHSf84V9cREMHyw1kX-baG5HzXWMt-hFLP30q6DpSUb2G_PhasKBfg$ > -- [5]https://urldefense.com/v3/__https://mail.python.org/mailman/listinfo/python-list__;!!Cn_UX_p3!hClFFo4XdiwQAhHxDbHA5zFr490Of9uheHSf84V9cREMHyw1kX-baG5HzXWMt-hFLP30q6DpSUb2G_PhasKBfg$ References Visible links 1. https://gist.github.com/atdt/ebafa299e843a767139b 2. https://urldefense.com/v3/__https:/docs.python.org/3/library/select.html__;!!Cn_UX_p3!hClFFo4XdiwQAhHxDbHA5zFr490Of9uheHSf84V9cREMHyw1kX-baG5HzXWMt-hFLP30q6DpSUb2G_OD5qBjeA$ 3. https://urldefense.com/v3/__https:/docs.python.org/3/library/selectors.html__;!!Cn_UX_p3!hClFFo4XdiwQAhHxDbHA5zFr490Of9uheHSf84V9cREMHyw1kX-baG5HzXWMt-hFLP30q6DpSUb2G_MwNjgO8A$ 4. https://urldefense.com/v3/__https:/mail.python.org/mailman/listinfo/python-list__;!!Cn_UX_p3!hClFFo4XdiwQAhHxDbHA5zFr490Of9uheHSf84V9cREMHyw1kX-baG5HzXWMt-hFLP30q6DpSUb2G_PhasKBfg$ 5. https://urldefense.com/v3/__https:/mail.python.org/mailman/listinfo/python-list__;!!Cn_UX_p3!hClFFo4XdiwQAhHxDbHA5zFr490Of9uheHSf84V9cREMHyw1kX-baG5HzXWMt-hFLP30q6DpSUb2G_PhasKBfg$ -- https://mail.python.org/mailman/listinfo/python-list
Re: Calling pselect/ppoll/epoll_pwait
Signalfd and select could probably be made to work if one codes around the race conditions pselect is provided to avoid. I’m not sure if using the GIL (for CPython) is sufficient or if a dedicated concurrency control (e.g. lock, mutex, semaphore) is necessary. An alternative is to call the C library function via a wrapper. I had need to use setfsuid on a project a couple of years ago and found this example: https://gist.github.com/atdt/ebafa299e843a767139b From: Python-list on behalf of Barry Date: Friday, December 2, 2022 at 7:02 PM To: Ian Pilcher Cc: python-list@python.org Subject: Re: Calling pselect/ppoll/epoll_pwait *** Attention: This is an external email. Use caution responding, opening attachments or clicking on links. *** > On 2 Dec 2022, at 20:03, Ian Pilcher wrote: > > Does Python provide any way to call the "p" variants of the I/O > multiplexing functions? > > Looking at the documentation of the select[1] and selectors[2] modules, > it appears that they expose only the "non-p" variants. > > [1] > https://urldefense.com/v3/__https://docs.python.org/3/library/select.html__;!!Cn_UX_p3!hClFFo4XdiwQAhHxDbHA5zFr490Of9uheHSf84V9cREMHyw1kX-baG5HzXWMt-hFLP30q6DpSUb2G_OD5qBjeA$<https://urldefense.com/v3/__https:/docs.python.org/3/library/select.html__;!!Cn_UX_p3!hClFFo4XdiwQAhHxDbHA5zFr490Of9uheHSf84V9cREMHyw1kX-baG5HzXWMt-hFLP30q6DpSUb2G_OD5qBjeA$> > [2] > https://urldefense.com/v3/__https://docs.python.org/3/library/selectors.html__;!!Cn_UX_p3!hClFFo4XdiwQAhHxDbHA5zFr490Of9uheHSf84V9cREMHyw1kX-baG5HzXWMt-hFLP30q6DpSUb2G_MwNjgO8A$<https://urldefense.com/v3/__https:/docs.python.org/3/library/selectors.html__;!!Cn_UX_p3!hClFFo4XdiwQAhHxDbHA5zFr490Of9uheHSf84V9cREMHyw1kX-baG5HzXWMt-hFLP30q6DpSUb2G_MwNjgO8A$> Can you use signalfd and select/poll/epoll? Barry > > -- > > Google Where SkyNet meets Idiocracy > > -- > https://urldefense.com/v3/__https://mail.python.org/mailman/listinfo/python-list__;!!Cn_UX_p3!hClFFo4XdiwQAhHxDbHA5zFr490Of9uheHSf84V9cREMHyw1kX-baG5HzXWMt-hFLP30q6DpSUb2G_PhasKBfg$<https://urldefense.com/v3/__https:/mail.python.org/mailman/listinfo/python-list__;!!Cn_UX_p3!hClFFo4XdiwQAhHxDbHA5zFr490Of9uheHSf84V9cREMHyw1kX-baG5HzXWMt-hFLP30q6DpSUb2G_PhasKBfg$> > -- https://urldefense.com/v3/__https://mail.python.org/mailman/listinfo/python-list__;!!Cn_UX_p3!hClFFo4XdiwQAhHxDbHA5zFr490Of9uheHSf84V9cREMHyw1kX-baG5HzXWMt-hFLP30q6DpSUb2G_PhasKBfg$<https://urldefense.com/v3/__https:/mail.python.org/mailman/listinfo/python-list__;!!Cn_UX_p3!hClFFo4XdiwQAhHxDbHA5zFr490Of9uheHSf84V9cREMHyw1kX-baG5HzXWMt-hFLP30q6DpSUb2G_PhasKBfg$> -- https://mail.python.org/mailman/listinfo/python-list
Re: Calling pselect/ppoll/epoll_pwait
> On 2 Dec 2022, at 20:03, Ian Pilcher wrote: > > Does Python provide any way to call the "p" variants of the I/O > multiplexing functions? > > Looking at the documentation of the select[1] and selectors[2] modules, > it appears that they expose only the "non-p" variants. > > [1] https://docs.python.org/3/library/select.html > [2] https://docs.python.org/3/library/selectors.html Can you use signalfd and select/poll/epoll? Barry > > -- > > Google Where SkyNet meets Idiocracy > > -- > https://mail.python.org/mailman/listinfo/python-list > -- https://mail.python.org/mailman/listinfo/python-list
