GIL - это боль

GIL

def sum_seq(n):
    result = 0
    for i in range(n):
        result += i

    return result

GIL

-	Time (sec)
python (sequence)	86.349
python (thread)	92.636
python (process)	22.646

Benchmark repo

GIL - Global Interpreter Lock

Гарантия, что только один поток исполняет код в единицу времени

Это не позволяет нормально пользоваться тредами

GIL

Так проще
- Писать код
- Поддерживать
Пока что никто не смог вырезать GIL, не замедлив однопоточные программы

It isn't Easy

to Remove the GIL

(Guido van van Rossum)

GIL

Python threads = OS threads (pthreads, etc)
Thread Scheduler = OS Scheduler

GIL

struct _gil_runtime_state {
    /* microseconds (the Python API uses seconds, though) */
    unsigned long interval;
    /* Last PyThreadState holding / having held the GIL. This helps us
       know whether anyone else was scheduled after we dropped the GIL. */
    _Py_atomic_address last_holder;
    /* Whether the GIL is already taken (-1 if uninitialized). This is
       atomic because it can be read without any lock taken in ceval.c. */
    _Py_atomic_int locked;
    /* Number of GIL switches since the beginning. */
    unsigned long switch_number;
    /* This condition variable allows one or several threads to wait
       until the GIL is released. In addition, the mutex also protects
       the above variables. */
    PyCOND_T cond;
    PyMUTEX_T mutex;
#ifdef FORCE_SWITCHING
    /* This condition variable helps the GIL-releasing thread wait for
       a GIL-awaiting thread to be scheduled and take the GIL. */
    PyCOND_T switch_cond;
    PyMUTEX_T switch_mutex;
#endif
};

https://github.com/python/cpython/blob/3.7/Include/internal/gil.h

GIL

void PyEval_RestoreThread(PyThreadState *tstate) {
    if (tstate == NULL)
        Py_FatalError("PyEval_RestoreThread: NULL tstate");
    assert(gil_created());

    int err = errno;
    take_gil(tstate);
    /* _Py_Finalizing is protected by the GIL */
    if (_Py_IsFinalizing() && !_Py_CURRENTLY_FINALIZING(tstate)) {
        drop_gil(tstate);
        PyThread_exit_thread();
        Py_UNREACHABLE();
    }
    errno = err;

    PyThreadState_Swap(tstate);
}



PyThreadState * PyEval_SaveThread(void)
{
    PyThreadState *tstate = PyThreadState_Swap(NULL);
    if (tstate == NULL)
        Py_FatalError("PyEval_SaveThread: NULL tstate");
    assert(gil_created());
    drop_gil(tstate);
    return tstate;
}

https://github.com/python/cpython/blob/3.7/Python/ceval.c

GIL

#define Py_BEGIN_ALLOW_THREADS { \
                        PyThreadState *_save; \
                        _save = PyEval_SaveThread();

#define Py_END_ALLOW_THREADS    PyEval_RestoreThread(_save); \
                 }

https://github.com/python/cpython/blob/3.7/Include/ceval.h

{
  PyThreadState *_save;
  _save = PyEval_SaveThread();

  /* ... Do some blocking I/O operation ... */

  PyEval_RestoreThread(_save);
}

Что делать будем?

1. ~~Не использовать питон~~

2. Использовать другой интерпретатор

- pypy-stm

- Jython

- IronPython

3. Писать все критические части

на C/C++, отпускать GIL руками

4. Multiprocessing

C-extensions

#include "sum_seq.h"

unsigned long long int sum_seq(unsigned long long int n) {
    unsigned long long int result = 0, i = 0;

    for (;i < n; i++) {
        result += i;
    }

    return result;
}

def sum_seq(n):
    result = 0
    for i in range(n):
        result += i

    return result

unsigned long long int sum_seq(unsigned long long int n);

sum_seq.h

sum_seq.c

C-extensions

#include <Python.h>
#include "sum_seq.h"


static PyObject *sum_seq_sum_seq(PyObject *self, PyObject *args);

static PyMethodDef module_methods[] = {
    {"sum_seq", sum_seq_sum_seq, METH_VARARGS, NULL},
    {NULL, NULL, 0, NULL}
};

static struct PyModuleDef moduledef = {
    PyModuleDef_HEAD_INIT,
    "sum_seq",  // module name
    NULL, // module docstring
    -1,
    module_methods,
    NULL,
    NULL,
    NULL,
    NULL,
};

PyObject *PyInit_sum_seq(void){
    PyObject *module = PyModule_Create(&moduledef);
    if (module == NULL)
        return NULL;
    return module;
}

_sum_seq.c

C-extensions

static PyObject *sum_seq_sum_seq(PyObject *self, PyObject *args){
    unsigned long long int n = 0, value = 0;

    if (!PyArg_ParseTuple(args, "K", &n)){
        return NULL;
    }

    value = sum_seq(n);

    PyObject *ret = Py_BuildValue("K", value);
    return ret;
}

_sum_seq.c

C-extensions

from setuptools import setup, Extension

setup(
    name="sum_seq",
    ext_modules=[
        Extension("sum_seq.c.sum_seq", 
                  sources=["./sum_seq/c/_sum_seq.c", "./sum_seq/c/sum_seq.c"])
    ]
)

setup.py

C-extensions

-	Time (sec)
python (sequence)	86.349
python (thread)	92.636
python (process)	22.646
c (sequence)	0.66055
c (thread)	0.66104

Benchmark repo

C-extensions

static PyObject *sum_seq_sum_seq(PyObject *self, PyObject *args){
    unsigned long long int n = 0, value = 0;

    if (!PyArg_ParseTuple(args, "K", &n)){
        return NULL;
    }

    Py_BEGIN_ALLOW_THREADS
    // ^^^^^^^^^^^^^^^^^^^

    value = sum_seq(n);

    Py_END_ALLOW_THREADS
    // ^^^^^^^^^^^^^^^^^

    PyObject *ret = Py_BuildValue("K", value);
    return ret;
}

_sum_seq.c

C-extensions

-	Time (sec)
python (sequence)	86.349
python (thread)	92.636
python (process)	22.646
c (sequence)	0.66055
~~c (thread)~~	~~0.66104~~
c (thread)	0.18879

Benchmark repo

C-extensions

htop здорового человека

htop ~~питониста~~ курильщика

C-extensions

ВСЁ ЗЕЛЁНЕНЬКОЕ!!1111
NO GIL
Мечты сбылись

Нужно писать обвязку (docs)
Нужно писать на С

А можно ли без обвязок (нет)?

def sum_seq(n):
    cdef long long unsigned int result = 0, i = 0;
    cdef long long unsigned int n_internal = n;

    with nogil:
        for i in range(n_internal):
            result += i

    return result

def sum_seq(n):
    result = 0
    for i in range(n):
        result += i

    return result

sum_seq.pyx

Cython

from setuptools import setup, Extension
from Cython.Build import cythonize

setup(
    name="sum_seq",
    ext_modules=[
        Extension("sum_seq.c.sum_seq", 
                  sources=["./sum_seq/c/_sum_seq.c", "./sum_seq/c/sum_seq.c"])
    ] + cythonize("sum_seq/cython/sum_seq.pyx",
                  compiler_directives={"language_level": 3}),
)

setup.py

Cython

-	Time (sec)
python (sequence)	86.349
python (thread)	92.636
python (process)	22.646
c (sequence)	0.66055
~~c (thread)~~	~~0.66104~~
c (thread)	0.18879
cython (sequence)	0.65923
cython (thread)	0.19168

Cython

Benchmark repo

from gensim.downloader import load
from gensim.models import Word2Vec

corpus = load("text8")
model = Word2Vec(corpus)

print(model.most_similar("cat"))

"""
[(u'dog', 0.830856204032898),
 (u'panda', 0.7922875285148621),
 (u'pig', 0.7816621661186218),
 (u'goat', 0.779694676399231),
 (u'bee', 0.7739807367324829),
 (u'ass', 0.7661241292953491),
 (u'hamster', 0.761398196220398),
 (u'blonde', 0.7453086376190186),
 (u'bird', 0.7418307065963745)]
"""

Cython

Gensim GSoC 2018

Cython

Gensim GSoC 2018

Cython

Gensim GSoC 2018

Cython

Gensim GSoC 2018

[pid 19844] 18:11:40.165364 futex(0x55f71dd9d290, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, 0xffffffff <unfinished ...>
[pid 19847] 18:11:40.165447 futex(0x55f71dd9d290, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, 0xffffffff <unfinished ...>
[pid 19845] 18:11:40.165466 futex(0x55f71dd9d290, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, 0xffffffff <unfinished ...>
[pid 19843] 18:11:40.165479 futex(0x55f71dd9d290, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, 0xffffffff <unfinished ...>
[pid 19842] 18:11:40.165510 futex(0x55f71dc5b220, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, 0xffffffff <unfinished ...>
[pid 19704] 18:11:40.165525 futex(0x55f71ebf1cd0, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, 0xffffffff <unfinished ...>
[pid 19846] 18:11:40.167154 futex(0x55f71dd9d290, FUTEX_WAKE_PRIVATE, 1) = 1 <0.000016>
[pid 19844] 18:11:40.167193 <... futex resumed> ) = 0 <0.001755>
[pid 19846] 18:11:40.167204 futex(0x55f71dc5b220, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, 0xffffffff <unfinished ...>
[pid 19844] 18:11:40.167419 futex(0x55f71dd9d290, FUTEX_WAKE_PRIVATE, 1) = 1 <0.000015>
[pid 19843] 18:11:40.167460 <... futex resumed> ) = 0 <0.001973>
[pid 19843] 18:11:40.167485 futex(0x55f71dd9d290, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, 0xffffffff <unfinished ...>
[pid 19844] 18:11:40.167500 futex(0x55f71dd9d290, FUTEX_WAKE_PRIVATE, 1 <unfinished ...>
[pid 19843] 18:11:40.167511 <... futex resumed> ) = -1 EAGAIN (Resource temporarily unavailable) <0.000015>
[pid 19847] 18:11:40.167523 <... futex resumed> ) = 0 <0.002065>
[pid 19844] 18:11:40.167532 <... futex resumed> ) = 1 <0.000028>
[pid 19847] 18:11:40.167541 futex(0x55f71dd9d290, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, 0xffffffff <unfinished ...>
[pid 19844] 18:11:40.167552 futex(0x55f71dd9d290, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, 0xffffffff <unfinished ...>
[pid 19843] 18:11:40.167562 futex(0x55f71dc5b220, FUTEX_WAKE_PRIVATE, 1) = 1 <0.000011>
[pid 19842] 18:11:40.167584 <... futex resumed> ) = 0 <0.002066>
[pid 19842] 18:11:40.167599 futex(0x55f71dd9d290, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, 0xffffffff <unfinished ...>
[pid 19843] 18:11:40.174995 futex(0x55f71dd9d290, FUTEX_WAKE_PRIVATE, 1) = 1 <0.000009>
[pid 19843] 18:11:40.175030 futex(0x55f71dc5b220, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, 0xffffffff <unfinished ...>
[pid 19845] 18:11:40.175058 <... futex resumed> ) = 0 <0.009584>
[pid 19845] 18:11:40.175136 futex(0x55f71dd9d290, FUTEX_WAKE_PRIVATE, 1) = 1 <0.000058>
[pid 19847] 18:11:40.175206 <... futex resumed> ) = 0 <0.007660>
[pid 19847] 18:11:40.175221 futex(0x55f71dd9d290, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, 0xffffffff <unfinished ...>
[pid 19845] 18:11:40.175233 futex(0x55f71dd9d290, FUTEX_WAKE_PRIVATE, 1 <unfinished ...>
[pid 19847] 18:11:40.175242 <... futex resumed> ) = -1 EAGAIN (Resource temporarily unavailable) <0.000013>
[pid 19847] 18:11:40.175265 futex(0x55f71dd9d290, FUTEX_WAKE_PRIVATE, 1) = 1 <0.000014>
[pid 19845] 18:11:40.175290 <... futex resumed> ) = 1 <0.000054>
[pid 19847] 18:11:40.175298 futex(0x55f71dd9d290, FUTEX_WAKE_PRIVATE, 1 <unfinished ...>
[pid 19844] 18:11:40.175308 <... futex resumed> ) = 0 <0.007750>
[pid 19847] 18:11:40.175316 <... futex resumed> ) = 0 <0.000013>
[pid 19842] 18:11:40.175326 <... futex resumed> ) = 0 <0.007721>
[pid 19847] 18:11:40.175338 futex(0x55f71dd9d290, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, 0xffffffff <unfinished ...>
[pid 19845] 18:11:40.175351 futex(0x55f71dd9d290, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, 0xffffffff <unfinished ...>
[pid 19842] 18:11:40.175365 futex(0x55f71dd9d290, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 0, NULL, 0xffffffff <unfinished ...>
[pid 19844] 18:11:40.175377 futex(0x55f71dd9d290, FUTEX_WAKE_PRIVATE, 1 <unfinished ...>
[pid 19845] 18:11:40.175399 <... futex resumed> ) = -1 EAGAIN (Resource temporarily unavailable) <0.000038>
[pid 19847] 18:11:40.175409 <... futex resumed> ) = 0 <0.000065>
[pid 19845] 18:11:40.175417 futex(0x55f71dd9d290, FUTEX_WAKE_PRIVATE, 1 <unfinished ...>
[pid 19847] 18:11:40.175427 futex(0x55f71dd9d290, FUTEX_WAKE_PRIVATE, 1 <unfinished ...>
[pid 19845] 18:11:40.175436 <... futex resumed> ) = 0 <0.000014>
[pid 19847] 18:11:40.175444 <... futex resumed> ) = 0 <0.000013>
[pid 19845] 18:11:40.175452 futex(0x55f71dd9d290, FUTEX_WAKE_PRIVATE, 1 <unfinished ...>
[pid 19847] 18:11:40.175461 futex(0x55f71dd9d290, FUTEX_WAKE_PRIVATE, 1 <unfinished ...>
[pid 19845] 18:11:40.175471 <... futex resumed> ) = 0 <0.000013>
[pid 19847] 18:11:40.175478 <... futex resumed> ) = 0 <0.000013>
[pid 19845] 18:11:40.175486 futex(0x55f71dd9d290, FUTEX_WAKE_PRIVATE, 1 <unfinished ...>
[pid 19847] 18:11:40.175496 futex(0x55f71dd9d290, FUTEX_WAKE_PRIVATE, 1 <unfinished ...>

Cython

Gensim GSoC 2018

strace: Process 17570 attached with 9 threads
strace: [ Process PID=17707 runs in x32 mode. ]
strace: [ Process PID=17707 runs in 64 bit mode. ]
% time     seconds  usecs/call     calls    errors syscall
------ ----------- ----------- --------- --------- ----------------
 99.32   47.545466           8   5848739    621257 futex
  0.44    0.208902           1    380473           read
  0.24    0.114486          31      3736           munmap
  0.00    0.000610           1       534           close
  0.00    0.000591           1       549           write
  0.00    0.000524           1       525           openat
  0.00    0.000330           1       548           stat
  0.00    0.000258           0      1050           fstat
  0.00    0.000142           0       548           getpid
  0.00    0.000064           8         8           madvise
  0.00    0.000014           0       146           mprotect
  0.00    0.000003           3         1           rt_sigaction
------ ----------- ----------- --------- --------- ----------------
100.00   47.871390               6236857    621257 total

Cython

Gensim GSoC 2018

def train_batch(..., sentences, ...):
    # Initialization code (cast python config to C types)
    ...

    # Convert batch to needed format (for NOGIL)
    ...

    with nogil:
        for sent_idx in range(effective_sentences):
            # Training
            ...

Cython

Gensim before GSoC 2018

def train_epoch(..., corpus_file, ...):
  # Initialization code (cast python config to C types)
  ...
  input_stream = get_stream_from(corpus_file)

  with nogil:
      input_stream.reset()
      while not (input_stream.is_eof() or 
                 total_words > expected_words / c.workers):
          sentences = input_stream.next_batch()

          # Convert batch to needed format 
          ...

          # Training
          ...

Cython

Gensim after GSoC 2018

More info (benchmark, usage, etc)

Cython

Gensim GSoC 2018

Спасибо

Ivan Menshikh

menshikh_iv
menshikh-iv
menshikh.iv@gmail.com

GIL - это боль

By Ivan Menshikh

GIL - это боль

1,492

Ivan Menshikh

menshikh_iv

GIL - это боль

GIL

GIL

GIL - Global Interpreter Lock

GIL

GIL

GIL

GIL

GIL

GIL

Что делать будем?

C-extensions

C-extensions

C-extensions

C-extensions

C-extensions

C-extensions

C-extensions

C-extensions

C-extensions

Cython

Cython

Cython

Cython

Gensim GSoC 2018

Cython

Gensim GSoC 2018

Cython

Gensim GSoC 2018

Cython

Gensim GSoC 2018

Cython

Gensim GSoC 2018

Cython

Gensim GSoC 2018

Cython

Gensim before GSoC 2018

Cython

Gensim after GSoC 2018

Cython

Gensim GSoC 2018

Спасибо

GIL - это боль

More from Ivan Menshikh