GIL

„CPython cannot into threads”

1992

„CPython cannot into threads”❌

„CPython cannot into threads”„CPython can run only on single core”

❌

PyPyJythonCPythonIronPythonBrython

PyPyJythonCPythonIronPythonBrython

PyPyJythonCPythonIronPythonBrython

Python

C

Python

C

„CPython cannot into threads”„CPython can run only on single core”

❌

❌

„CPython cannot into threads”„CPython can run only on single core”"CPython process can execute Python bytecode in one thread at the time"

❌

❌

✓

kolodziejj.info@unit03

Disclaimer

So what’s the hassle?

Misconceptions

CC-SA-BY, http://dibujando.net/dib/cthulhu-96836

Evolution

Concurrencyvs.

parallelism

GILfinally

Protectorof

CPython realm

Reference counters

1. Tracing garbage collection2. Reference counting3. ...

1. Tracing garbage collection2. Reference counting

int

1. Tracing garbage collection2. Reference counting

3

1. Tracing garbage collection2. Reference counting

0

Internal global state

C-mutable data structuresdict, list, …

C-mutable data structuresdict, list, …str, tuple, int

Binary modulesand extensions

Cost?

In single-threaded code?It doesn’t matter

(duh)

On single core?It doesn’t matter

In multi-threaded I/O-bound code?

It may not matter

With binary extensions?It may not matter

>= 3.2

1

1

2

1

2

Can Ihas GIL?

Nope.

1

2switch interval

2

1

Can Ihas GIL?

2

1

Can Ihas GIL?

Yes!

2

1

Can Ihas GIL?

Nope.

2

1

gil_drop_request = 1

2

1

gil_drop_request?

2

1

2

1

switch_cond?gil_last_holder?

2

1

<= 2.7- 2010

„ticks”

>>> print(„foo”)>>> -1 in range(100000000)

>>> print(„foo”)>>> -1 in range(100000000)>>> n -= 1

„check”„check” „check”

N „ticks” N „ticks” N = 100

100s ms few ms

2

1

Can Ihas GIL?

Nope.

And now? And now?

Nope. Nope.

2

1

Can Ihas GIL?

Nope.

And now? And now?

Nope. Nope.

Aw yiss

PyPyJythonCPythonIronPythonBrython

PyPyJythonCPythonIronPythonBrython

PyPyJythonCPythonIronPythonBrython

(but: STM)

PyPyJythonCPythonIronPythonBrython

RubyPythonGo

RubyPythonGo

RubyPythonGoroutines

RubyPythonGoroutineschannels

More!

multiprocessingimport

multiprocessingbinary extensions

cdef int foo = 0

multiprocessingbinary extensions

cdef int foo = 0with nogil: ...

multiprocessingbinary extensions

Py_BEGIN_ALLOW_THREADS Py_END_ALLOW_THREADS

multiprocessingbinary extensionsasynchronous I/O

Revolution?

C

Requirements

1. Single-threaded and multi-threaded I/O-bound performance2. C extensions compatibility3. Complexity

1. Single-threaded and multi-threaded I/O-bound performance2. C extensions compatibility3. Complexity

1. Single-threaded and multi-threaded I/O-bound performance2. C extensions compatibility3. Complexity

1996

Free-threading patch

Free-threading patchsubinterpreters

Free-threading patchsubinterpreters

GILectomy

Free-threading patchsubinterpreters

GILectomybuffered

reference counting

Free-threading patchsubinterpreters

GILectomy

thread

-privat

e

locking

buffered

reference counting

Free-threading patchsubinterpreters

GILectomy

thread

-privat

e

locking

buffered

reference counting

immortal objects

--without-gilPy_LOCK(o)Py_UNLOCK(o)

Free-threading patchsubinterpreters

GILectomy

What to do?

What to do?nothing

What to do?nothing

more research

What to do?nothing

more researchmigrate to 3.5 (3.6 even!)

What to do?nothing

more researchmigrate to 3.5 (3.6 even!)

assert the baseline, then act

kolodziejj.info/talks/gil/

Thank you! :)

kolodziejj.info/talks/gil/

What to do?nothing

more researchmigrate to 3.5 (3.6 even!)

assert the baseline, then actcontribute !