A Better Python for the JVM

A better Python
for the JVM
Tobias Ivarsson<tobias@thobe.org>

twitter:
@thobe
blog: http://journal.thobe.org

$ whoami
tobias (Tobias Ivarsson)
• M.Sc. in Computer Science and Engineering
from Linköping University, Sweden
• Jython Committer / Compiler zealot
• Javame why our graph database (Neo4j) kicks ass
Ask
developer at Neo Technology

Check out http://neo4j.org (it works with Python)

• High tech. / low trafﬁc:
twitter: @thobe
blog: http://journal.thobe.org
website: http://www.thobe.org - check for slides

• Overview of the “Advanced Compiler”
project

• Performance ﬁgures
• Python / JVM mismatch
• Getting better
• Summary

Project motivation

• The ultimate goal is a faster Jython
• The new compiler is just a component to
get there
• Focus is on representation of Python code
on the JVM

What does Code
Representation include?
• Function/Method/Code object
representation
• Scopes. How to store locals and globals
• Call frame representation
• Affects sys._getframe()
• The representation of builtins
• Mapping of python attributes to the JVM

Compiler tool chain
AST
Source code Parser AST Analyzer Compiler The “spine” of the
compiler. The main part.
Code Info This is the same in any
per scope compiler in Jython, and
similar to other systems,
CPython in particular, as
well.

Compiler tool chain
AST
Source code Parser AST Analyzer Compiler This is the structure of
the compiler in Jython
Code Info today.
per scope

Java
byte code

Jython
runtime
system JVM

Compiler tool chain
AST
Source code Parser AST Analyzer Compiler IR Transformer
Code Info
per scope
IR
The advanced compiler
adds t wo more steps
to the compilation
process.
The analyzer and
Codegen
compiler step also
Java
Jython change.
byte code

runtime
system JVM

Compiler tool chain
AST
Code Info
This ﬂexibility makes it per scope
possible to output many IR
different code formats.
Even bundle together multiple Python
formats for one module.
byte code
Codegen
Java
Jython byte code
Interpreter
runtime
system JVM

Compiler tool chain
AST
Code Info
It is also possible to compile, per scope
and re-compile code with
more information from the
actual runtime data.
Codegen
IR
IR
Java
+ runtime
byte code
Jython info

Interpreter
runtime
system JVM

The Intermediate
Representation

• “sea of nodes” style SSA
• Control flow and data flow both
modeled as edges between nodes
• Simplifies instruction re-ordering

Parrotbench
• 7 tests, numbered b0-b6
• Test b1 omitted
• Tests inﬁnite recursion and expects
recursion limit exception
• Allocates objects while recursing
• Not applicable for Jython

Running parrotbench
• Python 2.6 vs Jython 2.5 (trunk)
• Each test executes 3 times, minimum taken
• Total time of process execution, including
startup also measured
• Jython also tested after JVM JIT warmup
• Warmup for about 1 hour...
110 iterations of each test

The tests
(rough understanding)
• b0 parses python in python
• b2 computes pi
• b3 sorts random data
• b4 more parsing of python in python
• b5 tests performance of builtins
• b6 creates large simple lists/dicts

Python 2.6
Test Time (ms)
b0 1387
b2 160
b3 943
b4 438
b5 874
b6 1079
Total* (incl.VM startup) 15085
* Total time is for three iterations, other
times is the best iteration of those three

Jython 2.5b
(Preview version available at PyCon)
Test Time (ms) Time (ms)
(without JIT warmup) (with JIT warmup)

b0 4090 2099
b2 202 107
b3 3612 1629
b4 1095 630
b5 3044 2161
b6 2755 2237
Total* (incl.VM startup) 51702 Not applicable

Jython 2.5+ Jython 2.5.0 Final has
an embarrassing
performance issue on
list multiplication that

(Snapshot from June 24 2009) got introduced when
the list implementation
was made thread safe.

Test Time (ms) Time (ms)
(without JIT warmup) (with JIT warmup)

b0 2968 2460
b2 202 124
b3 2255 2030
b4 875 742
b5 4036 2291
b6 2279 2276
Total* (incl.VM startup) 57279 Not applicable

CPython2.6 vs Jython2.5 Work on thread safety and compatibility has
made Jython *slower* but better.
Performance is a later focus.

Python 2.6 Jython 2.5b Jython 2.5+

60,000

45,000

30,000

15,000

0
Total runtime Excluding VM startup

CPython2.6 vs Jython2.5
UnJITed
performance
improved due to
lower call overhead
b0 b2 b3 b4 b5 b6 and better dict. JITed
performance worse
due to thread safety
ﬁixes.
15,000

11,250

7,500

3,750

0
Python 2.6 Jython 2.5b with warmup Jython 2.5+ with warmup

CPython2.6 vs Jython2.5
Python 2.6 Jython 2.5b Jython 2.5b with warmup
Jython 2.5+ Jython 2.5+ with warmup
5,000

3,750

2,500

1,250

0
b0 b2 b3 b4 b5 b6

JRuby is a good indicator
for the performance we
could reach with Jython.
It’s a similar language on
the same platform.
Therefore a comparison
and analysis is
interesting.

Is JRuby
faster than Jython?

Adding two numbers
# Jython
def adder(a,b):
return a+b

# JRuby
def adder(a,b)
a+b
end

Execution times
(ms for 400000 additions)
Jython JRuby

700ms
697ms

525ms
466ms

350ms

175ms

0ms
Without counter

Why is JRuby faster?

• JRuby has had more work on performance
• Jython work has been focused on 2.5 compatibility

• Next release will start to target performance

• JRuby has a shorter call path
• JRuby does Call Site caching

Counting the number of
additions - Jython
from threading import Lock
count = 0
lock = Lock()
def adder(a,b):
global count
with lock:
count += 1
return a+b

Counting the number
of additions - JRuby
class Counting
def adder(a,b)
@mutex.synchronize {
@count = @count + 1
}
a + b
end
end

Execution times
(ms for 400000 additions)
Jython (Lock) JRuby (Mutex) Jython (AtomicInteger)

50,000ms
I included AtomicInteger to
46,960ms verify that the problem
was with the
synchronization primitives.
37,500ms

25,000ms

12,500ms

4,590ms
0ms 2,981ms
With counter

Why is JRuby faster?

• JRuby has had more work on performance
• JRuby has lower call overhead
• JRuby Mutex is easier for the JVM to
optimize than Jython Lock
• Because of JRubys use of closures

Call overhead
comparison
• Python wrapper around • Java code implementing
Java primitives the Ruby logic
• Call to Python code • Lock
• Reﬂective Java call • Direct call to closure
• Lock • Unlock
• Execute actual code
• Call to Python code
• Reﬂective Java call
• Unlock

Call frames
• A lot of Python code depend on reﬂecting
call frames
• Every JVM has call frames, but only expose
them to debuggers
• Current Jython is naïve about how frames
are propagated
• Simple prototyping hints at up to 2x boost

Extremely late binding

• Every binding can change
• The module scope is volatile
• Even builtins can be overridden

Exception handling
• Exception type matching in Python is a
sequential comparison.
• Exception type matching in the JVM is done
on exact type by the VM.
• Exception types are speciﬁed as arbitrary
expressions.
• No way of mapping Python try/except
directly to the JVM.

Blocks of Code

• The JVM has a size limit
• The JVM JIT has an even smaller size limit

Call frames

• Analyze code - omit unnecessary frames
• Fall back to java frames for pdb et.al.
• Treat locals, globals, dir, exec, eval as special
• Pass state - avoid central stored state
• sys._getframe() is an implementation detail

Late binding

• Ignore it and provide a fail path
• Inline builtins
• Turn for i in range(...): ... into a java loop
• Do direct invocations to members of the
same module

JVM Code analysis

• Create faux closures
• Separate code blocks that evaluate in
same scope
• Will also help with the code size limit

Exception handling

• The same late binding optimizations
+ optimistic exception handler
restructuring gets us far

Reaping the fruits of
the future JVMs
• Invokedynamic can perform most optimistic
direct calls and provide the fail path
• Interface injection make all java objects
look like python objects
• Gives improved integration between
different dynamic languages even more
• The advanced compiler makes a perfect
platform for integrating this

The “Advanced Jython
compiler” project
• Not just a compiler - but everything close
to the compiler - code representation
• A platform for moving forward
• First and foremost an enabling tool
• Actual improvement happens elsewhere

Performance
• Jython has decent performance
• On some benchmarks Jython is better
• For single threaded applications CPython is
still slightly better
• Don’t forget: Jython can do threading
• Long running applications beneﬁt from the
JVM - Jython is for the server side
• We are only getting started...

Python / JVM mismatch
- Getting better -
• Most of the problems comes from trying to
mimic CPython to closely
• Future JVMs are a better match
• Break code into smaller chunks
• Shorter call paths
• Optimistic optimizations are the way to go

Thank you!
Questions?

Tobias Ivarsson
<tobias@thobe.org>
twitter:
@thobe
blog:

http://journal.thobe.org

A Better Python for the JVM

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