Best way to delay a few milliseconds within nogil block?

[njan...@gmail.com]

What is the best way to delay a few milliseconds within a nogil block, that's within a cdef function?  time.sleep() seems to require the GIL, from my inspection of the cython-generated C code.  I'm assuming this because it's incrementing and decrementing references, which I assume must be done within the GIL.  Indeed, if I use the "nogil" suffix within my cdef call, I get the following error: "Constructing Python tuple not allowed without gil"

For context, in my application, I'm polling data from a piece of PCIe test equipment, using their published C API, in a thread.  The C API  does not support callbacks, just polling.  I must poll it, quickly.  Any data received is put into a pure-C queue implementation.  Another thread will consume the queued data, and compute things with it, when there's data available.  This second thread can be run more leisurely.  

Is there a simple cross-platform C function that I could call, that just sleeps for a specified time?  While I could cimport unistd.h's usleep() function, that's POSIX only.  For Windows, I coulid call Sleep()

This is my best-guess of how it should be done, but it seems clunky.

IF UNAME_SYSNAME == "Windows":

    cdef extern from "windows.h" nogil:

        void Sleep(uint32_t dwMilliseconds)

    cdef void cross_platform_sleep(uint32_t milliseconds) nogil:

        Sleep(milliseconds)

ELSE:

    from posix.unistd cimport usleep

    cdef void cross_platform_sleep(uint32_t milliseconds) nogil:

        usleep(milliseconds * 1000)

Is this a good way to accomplish it, or is there a better or simpler way?

Thanks!

[Stefan Behnel]

njan...@gmail.com schrieb am 02.10.20 um 19:28:

I think that's the right idea, but you should do it in C using #ifdef's,
and not in Cython.

Since this is a good example for platform adaptation, I took the liberty to
add it to the documentation:

https://cython.readthedocs.io/en/latest/src/userguide/external_C_code.html#including-verbatim-c-code

Stefan

[Robert Bradshaw]

I ran into this issue as well and created https://pypi.org/project/cytime

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[Stefan Behnel]

Robert Bradshaw schrieb am 03.10.20 um 07:53:

> I ran into this issue as well and created https://pypi.org/project/cytime

There's also

https://github.com/cython/cython/issues/3733

https://github.com/cython/cython/pull/3767

Stefan

[Neil Jansen]

Thanks Stefan and Robert.  cytime looks like a great short-term fix and long-term, hopefully that pull request will get merged in. 

I had another similar question. I can't use a threading.RLock outside of the GIL either.  I'm not a C (or C++ for that matter) expert but I don't recall there being any standard library implementations of mutexes or rlocks in the C standard library.  The Cython library compiles to C, not C++, so I'm not keen on using the C++ standard library threading or locks although I might be inclined to use them if no other choices are available.  So I have the same problem here.  I'd like to use a mutex outside of the GIL to protect my custom queue implementation between the producer thread and the consumer thread.  And at a minimum it would need to compile to Windows and Linux.  Any ideas or suggestions?

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