Low Level RPython

Talk at Chicago Python User's Group. February 9, 2012. Video at https://www.youtube.com/watch?v=kkt_BtR9Kzk

Transcript

1. Low Level RPython
   David Beazley
   http://www.dabeaz.com
   @dabeaz
   February 9, 2012
   

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2. PyPy Overview
   • PyPy is Python implemented in Python
   Interpreter
   (ANSI C)
   Python Program
   Interpreter
   (Python)
   Python Program
   CPython PyPy
   • Take the C version of the interpreter and
   rewrite it as a Python program.
   

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3. rpython
   • PyPy is actually implemented in "rpython"
   • rpython is not an "interpreter", but a
   restricted subset of the Python language
   Python
   rpython
   • It can run as valid Python code, but that's
   about the only similarity
   

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4. rpython
   • rpython is a completely different language
   • Python syntax, yes.
   • Must be compiled (like C, C++, etc.)
   • Static typing via type inference
   • Very different than anything you're used to
   

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5. A Simple Example
   • Example rpython code:
   # fib.py
   def fib(n):
   if n < 2:
   return 1
   else:
   return fib(n-1) + fib(n-2)
   # entry point. Like C main()
   def main(argv):
   print fib(int(argv[1]))
   return 0
   def target(*args):
   return main, None
   

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6. Translation (Compilation)
   • rpython translation
   bash % pypy/translator/goal/translate.py fib.py
   [platform:msg] Setting platform to 'host' cc=None
   [translation:info] Translating target as defined by
   hello
   [platform:execute] gcc-4.0 -c -arch x86_64 -O3 -
   fomit-frame-pointer -mdynamic-no-pic /var/folders/-
   \
   ... lots of additional output ...
   • Creates and compiles a C program into an exe
   bash % ./fib-c 38
   63245986
   bash %
   

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7. Performance
   • It runs pretty fast
   CPython 2.7 95.4s
   pypy 17.0s
   rpython 2.6s
   ANSI C (-O2) 2.1s
   • Almost as fast as ANSI C
   

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8. R is for Restricted
   • rpython allows no dynamic typing
   def add(x,y):
   return x+y
   def main(argv):
   r1 = add(2,3) # Ok
   r2 = add("Hello","World") # Error
   return 0
   • Functions can only have one type signature
   

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9. R is for Restricted
   • Containers can only have a single type
   numbers = [1,2,3,4,5] # Ok
   items = [1, "Hello", 3.5] # Error
   names = { # Ok
   'dabeaz' : 'David Beazley',
   'gaynor' : 'Alex Gaynor',
   }
   record = { # Error
   'name' : 'ACME',
   'shares' : 100
   }
   • Think C, not Python.
   

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10. R is for Restricted
    • Attributes can only be a single type
    class Pair(object):
    def __init__(self,x,y):
    self.x = x
    self.y = y
    a = Pair(2,3) # OK (first use)
    b = Pair("Hello","World") # Error
    • Again, think C
    

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11. Today's Topic
    • Going deeper into the generated C
    • Looking at the code
    • Studying efficiency
    • Accessing C libraries
    • ???
    

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12. Advance Head Explosion
    This is a pretty dark and poorly
    documented corner of rpython
    

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13. Looking at the C Code
    • rpython generates C code and places it into
    a temporary directory
    ...
    [translation:info] usession directory: /var/folders/M7/
    M7Q2OurGGbezUFSLGEgQZ++++TI/-Tmp-/usession-unknown-0
    [translation:info] created: /Users/beazley/Desktop/PyPyResearch/fib-c
    [Timer] Timings:
    [Timer] annotate --- 2.2 s
    [Timer] rtype_lltype --- 1.8 s
    [Timer] backendopt_lltype --- 1.2 s
    [Timer] stackcheckinsertion_lltype --- 0.0 s
    [Timer] database_c --- 16.7 s
    [Timer] source_c --- 2.8 s
    [Timer] compile_c --- 2.2 s
    [Timer] =========================================
    [Timer] Total: --- 26.8 s
    bash %
    

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14. Looking at the C Code
    • Go look for the "testing_1" directory
    bash % cd /var/folders/M7/M7Q2OurGGbezUFSLGEgQZ++++TI/-Tmp-/usession-unknown-0
    bash % cd testing_1
    bash % ls *.c
    data_objspace_flow_specialcase.c
    data_rlib_rdtoa.c
    data_rlib_rposix.c
    data_rlib_rstack.c
    data_rlib_rstack_1.c
    data_rpython_lltypesystem_rffi.c
    data_rpython_lltypesystem_rlist.c
    data_rpython_memory_gc_env.c
    data_rpython_memory_gc_minimark.c
    data_rpython_memory_gc_minimark_1.c
    data_rpython_memory_gctransform_framework.c
    debug_print.c
    implement.c
    nonfuncnodes.c
    objspace_flow_specialcase.c
    profiling.c
    ...
    

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15. Essential Files
    • Here's where most of the generated code
    from your program gets placed
    • implement.c (functions)
    • nonfuncnodes.c (globals)
    • structdef.h (data structures)
    • Look at them if you dare... yes.
    

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16. Example Code
    long pypy_g_fib(long l_n_0) {
    bool_t l_v280; bool_t l_v283; bool_t l_v286; bool_t l_v289;
    long l_v278; long l_v279; long l_v284; long l_v287; long l_v290;
    ...
    goto block0;
    block0:
    OP_INT_LT(l_n_0, 2L, l_v280);
    if (l_v280) {
    l_v294 = 1L;
    goto block5;
    }
    goto block1;
    block1:
    pypy_g_stack_check___();
    l_v282 = (&pypy_g_ExcData)->ed_exc_type;
    l_v283 = (l_v282 == NULL);
    if (!l_v283) {
    goto block8;
    }
    goto block2;
    block2:
    OP_INT_SUB(l_n_0, 1L, l_v284);
    l_v278 = pypy_g_fib(l_v284);
    PYPY_INHIBIT_TAIL_CALL();
    l_v285 = (&pypy_g_ExcData)->ed_exc_type;
    

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17. Example Code
    long pypy_g_fib(long l_n_0) {
    bool_t l_v280; bool_t l_v283; bool_t l_v286; bool_t l_v289;
    long l_v278; long l_v279; long l_v284; long l_v287; long l_v290;
    ...
    goto block0;
    block0:
    OP_INT_LT(l_n_0, 2L, l_v280);
    if (l_v280) {
    l_v294 = 1L;
    goto block5;
    }
    goto block1;
    block1:
    pypy_g_stack_check___();
    l_v282 = (&pypy_g_ExcData)->ed_exc_type;
    l_v283 = (l_v282 == NULL);
    if (!l_v283) {
    goto block8;
    }
    goto block2;
    block2:
    OP_INT_SUB(l_n_0, 1L, l_v284);
    l_v278 = pypy_g_fib(l_v284);
    PYPY_INHIBIT_TAIL_CALL();
    l_v285 = (&pypy_g_ExcData)->ed_exc_type;
    l_v286 = (l_v285 == NULL);
    It's a literal translation
    of flow-graphs into C
    (rather cryptic)
    

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18. Experimental Coding
    • You can try different things in rpython and
    go look at the output C code
    • A bit of a challenge
    • But interesting to study what happens
    

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19. Example: Objects
    class Stock(object):
    def __init__(self,name,shares,price):
    self.name = name
    self.shares = shares
    self.price = price
    s = Stock('ACME',50,123.45)
    // structdef.h
    ...
    struct pypy_cls_Stock0 {
    struct pypy_object0 s_super;
    struct pypy_rpy_string0 *s_inst_name;
    double s_inst_price;
    long s_inst_shares;
    }
    rpython
    

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20. Accessing C Code
    • If everything in PyPy is written in rpython,
    how does it access low-level C libraries?
    • os modules
    • time functions
    • math functions
    • General question: How would you access C
    code from any Python program?
    

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21. ctypes (CPython)
    • Perhaps you've used ctypes before...
    import ctypes
    mlib = ctypes.cdll.LoadLibrary("libm.dylib")
    sin = mlib.sin
    sin.argtypes = (ctypes.c_double,)
    sin.restype = ctypes.c_double
    ...
    x = sin(2)
    • rpython is kind of similar
    

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22. rpython rffi
    • Foreign Function Interface
    from pypy.rpython.lltypesystem import rffi
    sin = rffi.llexternal("sin", [rffi.DOUBLE], rffi.DOUBLE)
    cos = rffi.llexternal("cos", [rffi.DOUBLE], rffi.DOUBLE)
    ...
    • Declares external C functions with types
    • Can use in your rpython program
    y = sin(x) + cos(x)
    ...
    • Instructive to look at low-level C code
    

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23. rffi Commentary
    • The rpython rffi is highly developed
    • Most C primitive datatypes
    • Arrays
    • Structures
    • Pointers
    • Memory management
    • (More advanced example shortly)
    

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24. Configuration System
    • There is a C compilation/configuration system
    from pypy.translator.tool.cbuild import ExternalCompilationInfo
    from pypy.rpython.tool import rffi_platform as platform
    class CConfig:
    _compilation_info_ = ExternalCompilationInfo(
    includes = ['math.h'],
    libraries = ['m'],
    )
    M_PI = platform.DefinedConstantDouble('M_PI')
    M_E = platform.DefinedConstantDouble('M_E')
    config = platform.configure(CConfig)
    M_PI = config['M_PI']
    M_E = config['M_E']
    

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25. Configuration System
    • There is a C compilation/configuration system
    from pypy.translator.tool.cbuild import ExternalCompilationInfo
    from pypy.rpython.tool import rffi_platform as platform
    class CConfig:
    _compilation_info_ = ExternalCompilationInfo(
    includes = ['math.h'],
    libraries = ['m'],
    )
    M_PI = platform.DefinedConstantDouble('M_PI')
    M_E = platform.DefinedConstantDouble('M_E')
    config = platform.configure(CConfig)
    M_PI = config['M_PI']
    M_E = config['M_E']
    C compiler
    specification (includes,
    libraries, paths, etc.)
    

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26. Configuration System
    • There is a C compilation/configuration system
    from pypy.translator.tool.cbuild import ExternalCompilationInfo
    from pypy.rpython.tool import rffi_platform as platform
    class CConfig:
    _compilation_info_ = ExternalCompilationInfo(
    includes = ['math.h'],
    libraries = ['m'],
    )
    M_PI = platform.DefinedConstantDouble('M_PI')
    M_E = platform.DefinedConstantDouble('M_E')
    config = platform.configure(CConfig)
    M_PI = config['M_PI']
    M_E = config['M_E']
    Some "queries" for
    things you want to
    know from C
    

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27. Configuration System
    • There is a C compilation/configuration system
    from pypy.translator.tool.cbuild import ExternalCompilationInfo
    from pypy.rpython.tool import rffi_platform as platform
    class CConfig:
    _compilation_info_ = ExternalCompilationInfo(
    includes = ['math.h'],
    libraries = ['m'],
    )
    M_PI = platform.DefinedConstantDouble('M_PI')
    M_E = platform.DefinedConstantDouble('M_E')
    config = platform.configure(CConfig)
    M_PI = config['M_PI']
    M_E = config['M_E']
    Run the C compiler
    and get results back
    

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28. Configuration Comments
    • There is no centralized "configuration"
    • Individual program modules simply request
    information from the C compilation
    environment whenever they need it
    • Somehow (magically), the system will invoke the
    C compiler as needed.
    • It hurts my head...
    

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29. Final Demo
    

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30. Now What?!?
    • We haven't even talked about PyPy yet!
    • .... or the JIT
    • Implemented in rpython
    • So, all of this is just a starting point
    • More talks? (maybe)
    

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