[ python-Feature Requests-1453341 ] sys.setatomicexecution - for critical sections

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Feature Requests item #1453341, was opened at 2006-03-18 20:52
Message generated for change (Comment added) made by kxroberto
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Category: Python Interpreter Core
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: kxroberto (kxroberto)
Assigned to: Nobody/Anonymous (nobody)
Summary: sys.setatomicexecution -  for critical sections

Initial Comment:
In order to maintain threaded code uncomplicated (VHL)
and in order to avoid massive use of locks, when
introducing few critical non-atomic sections, it should
be possible to put out that practical hammer ..

    try:
        last_ci=sys.setcheckinterval(sys.maxint)
        critical_function()  # now runs atomically
    finally:
        sys.setcheckinterval(last_ci)
    #(sys.setcheckinterval assumed to return the last
value)


..by an official function/class (in sys or thread):


Maybe:
======

atomic = sys.setatomicexecution(mode)
try:
    print "Executing critical section"
finally:
    sys.setatomicexecution(atomic)

there should be different modes/levels for blocking :

* 0=None
* 1=block only python execution in other threads
* 2=block signals
* 4/5/7/15=block threads at OS level (if OS supports)
* 8=(reserved: block future sub-/stackless switching
inside current thread..)

see:
http://groups.google.de/group/comp.lang.python/browse_frm/thread/bf5461507803975e/3bd7dfa9422a1200

compare:
http://www.stackless.com/wiki/Tasklets#critical-sections

---

Also Python could define officially its time atoms
beyond CPU atoms in the docs (That also defines the VHL
usability of the language).

Thus thinks like single-element changes ...

obj.var=x  , d[key]=x , l.append(x) .pop()

should be guaranteed to work atomic/correct FOR EVER. 

l[slice],  d.keys() .items(), .. questionable? 
If not guaranteed for the future, offer duplicates for
speed critical key building blocks like: 
l.slice_atomic(slice), d.keys_atomic() ,...  in order
to make code compatible for the future. 

---

Extra fun for blowing up python libs for poeple who
don't want to learn that try..finally all the time:

copy/deepcopy/dump maybe could be enriched by
copy_atomic , deepcopy_atomic, dump_atomic - or just
RuntimeError tolerant versions,   deepcopy_save  (no
use of .iterxxx)



----------------------------------------------------------------------

>Comment By: kxroberto (kxroberto)
Date: 2006-03-18 22:54

Message:
Logged In: YES 
user_id=972995

or:

>>> atomic = sys.acquireatomicexecution(mode)
>>> try: 
... 	print 'critical section'
... finally:
... 	atomic.release()

>>> with sys.acquireatomicexecution(mode):
...     print 'critical section'



----------------------------------------------------------------------

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