Author: Armin Rigo <ar...@tunes.org> Branch: Changeset: r90360:75edc48a7774 Date: 2017-02-26 12:43 +0100 http://bitbucket.org/pypy/pypy/changeset/75edc48a7774/
Log: update the faq about the gil diff --git a/pypy/doc/faq.rst b/pypy/doc/faq.rst --- a/pypy/doc/faq.rst +++ b/pypy/doc/faq.rst @@ -156,19 +156,30 @@ Does PyPy have a GIL? Why? ------------------------------------------------- -Yes, PyPy has a GIL. Removing the GIL is very hard. The problems are -essentially the same as with CPython (including the fact that our -garbage collectors are not thread-safe so far). Fixing it is possible, -as shown by Jython and IronPython, but difficult. It would require -adapting the whole source code of PyPy, including subtle decisions about -whether some effects are ok or not for the user (i.e. the Python -programmer). +Yes, PyPy has a GIL. Removing the GIL is very hard. On top of CPython, +you have two problems: (1) GC, in this case reference counting; (2) the +whole Python language. -Instead, since 2012, there is work going on on a still very experimental -:doc:`Software Transactional Memory <stm>` (STM) version of PyPy. This should give -an alternative PyPy which works without a GIL, while at the same time -continuing to give the Python programmer the complete illusion of having -one. +For PyPy, the hard issue is (2): by that I mean issues like what occurs +if a mutable object is changed from one thread and read from another +concurrently. This is a problem for *any* mutable type: it needs +careful review and fixes (fine-grained locks, mostly) through the +*whole* Python interpreter. It is a major effort, although not +completely impossible, as Jython/IronPython showed. This includes +subtle decisions about whether some effects are ok or not for the user +(i.e. the Python programmer). + +CPython has additionally the problem (1) of reference counting. With +PyPy, the problem is simpler: we need to make our GC multithread-aware. +This is easier to do efficiently in PyPy than in CPython. It doesn't +solve the issue (2), though. + +Note that since 2012 there is work going on on a still very experimental +:doc:`Software Transactional Memory <stm>` version of PyPy. This should +give an alternative PyPy which works without a GIL, while at the same +time continuing to give the Python programmer the complete illusion of +having one. This work is currently a bit stalled because of its own +technical difficulties. Is PyPy more clever than CPython about Tail Calls? _______________________________________________ pypy-commit mailing list pypy-commit@python.org https://mail.python.org/mailman/listinfo/pypy-commit
