Author: Antonio Cuni <[email protected]>
Branch: extradoc
Changeset: r5534:14123b4ae075
Date: 2015-04-17 12:55 +0200
http://bitbucket.org/pypy/extradoc/changeset/14123b4ae075/
Log: introduce a real world example
diff --git a/talk/pycon-italy-2015/src/decode0.py
b/talk/pycon-italy-2015/src/decode0.py
new file mode 100644
--- /dev/null
+++ b/talk/pycon-italy-2015/src/decode0.py
@@ -0,0 +1,25 @@
+import sys
+import struct
+
+P1 = '\x0c\x00\x00\x00"\x00\x00\x00\x07\x00'
+P2 = '\x15\x00\x00\x00+\x00\x00\x00\x08\x00'
+
+PLIST = [P1, P2] * 2000
+
+def read_x(p):
+ return struct.unpack_from('l', p, 0)[0]
+
+def read_y(p):
+ return struct.unpack_from('l', p, 4)[0]
+
+def read_color(p):
+ return struct.unpack_from('i', p, 8)[0]
+
+def main():
+ res = 0
+ for p in PLIST:
+ x = read_x(p)
+ res += x
+ print res
+
+main()
diff --git a/talk/pycon-italy-2015/src/decode1.py
b/talk/pycon-italy-2015/src/decode1.py
new file mode 100644
--- /dev/null
+++ b/talk/pycon-italy-2015/src/decode1.py
@@ -0,0 +1,41 @@
+import sys
+import struct
+
+P1 = '\x0c\x00\x00\x00"\x00\x00\x00\x07\x00'
+P2 = '\x15\x00\x00\x00+\x00\x00\x00\x08\x00'
+
+PLIST = [P1, P2] * 2000
+
+class Field(object):
+
+ def __init__(self, fmt, offset):
+ self.fmt = fmt
+ self.offset = offset
+
+
+class Message(object):
+
+ def __init__(self, name, fields):
+ self._name = name
+ self._fields = fields
+
+ def read(self, buf, name):
+ f = self._fields[name]
+ return struct.unpack_from(f.fmt, buf, f.offset)[0]
+
+
+Point = Message('Point', {
+ 'x': Field('l', 0),
+ 'y': Field('l', 4),
+ 'color': Field('i', 8)
+ })
+
+
+def main():
+ res = 0
+ for p in PLIST:
+ x = Point.read(p, 'x')
+ res += x
+ print res
+
+main()
diff --git a/talk/pycon-italy-2015/talk.rst b/talk/pycon-italy-2015/talk.rst
--- a/talk/pycon-italy-2015/talk.rst
+++ b/talk/pycon-italy-2015/talk.rst
@@ -219,6 +219,220 @@
* inefficient code
+Virtuals
+--------
+
+- Remove unnecessary allocations
+
+- Remove unnecessary load/store
+
+- "Abstraction for free"
+
+
+Example
+--------
+
+- Real world example
+
+- Decoding binary messages
+
+- Messages: strings of bytes
+
+|small|
+|example<| |small| Point |end_small| |>|
+
+.. sourcecode:: C
+
+ struct Point {
+ long x;
+ long y;
+ int color;
+ }
+
+|end_example|
+|end_small|
+
+
+
+Example: low-level solution
+----------------------------
+
+|scriptsize|
+|example<| |small| decode0.py |end_small| |>|
+
+.. sourcecode:: python
+
+ P1 = '\x0c\x00\x00\x00"\x00\x00\x00\x07\x00\x00\x00'
+ P2 = '\x15\x00\x00\x00+\x00\x00\x00\x08\x00\x00\x00'
+
+ PLIST = [P1, P2] * 2000
+
+ def read_x(p):
+ return struct.unpack_from('l', p, 0)[0]
+
+ def main():
+ res = 0
+ for p in PLIST:
+ x = read_x(p)
+ res += x
+ print res
+
+|end_example|
+|end_scriptsize|
+
+Example: low-level solution
+----------------------------
+
+|scriptsize|
+|example<| |small| decode0.py trace |end_small| |>|
+
+.. sourcecode:: python
+
+ debug_merge_point(1, 1, '<code object read_x> #0 LOAD_GLOBAL')
+ debug_merge_point(1, 1, '<code object read_x> #3 LOOKUP_METHOD')
+ debug_merge_point(1, 1, '<code object read_x> #6 LOAD_CONST')
+ debug_merge_point(1, 1, '<code object read_x> #9 LOAD_FAST')
+ debug_merge_point(1, 1, '<code object read_x> #12 LOAD_CONST')
+ debug_merge_point(1, 1, '<code object read_x> #15 CALL_METHOD')
+ +606: i91 = strlen(p88)
+ +609: i92 = int_lt(i91, 4)
+ guard_false(i92, descr=<Guard0xb3a14b20>)
+ +618: i93 = strgetitem(p88, 0)
+ +622: i94 = strgetitem(p88, 1)
+ +632: i95 = int_lshift(i94, 8)
+ +635: i96 = int_or(i93, i95)
+ +637: i97 = strgetitem(p88, 2)
+ +653: i98 = int_lshift(i97, 16)
+ +656: i99 = int_or(i96, i98)
+ +658: i100 = strgetitem(p88, 3)
+ +662: i101 = int_ge(i100, 128)
+ guard_false(i101, descr=<Guard0xb3a14ac0>)
+ +674: i102 = int_lshift(i100, 24)
+ +677: i103 = int_or(i99, i102)
+
+|end_example|
+|end_scriptsize|
+
+Example: better API
+---------------------
+
+|scriptsize|
+|example<| |small| decode1.py |end_small| |>|
+
+.. sourcecode:: python
+
+ class Field(object):
+ def __init__(self, fmt, offset):
+ self.fmt = fmt; self.offset = offset
+
+ class Message(object):
+ def __init__(self, name, fields):
+ self._name = name; self._fields = fields
+
+ def read(self, buf, name):
+ f = self._fields[name]
+ return struct.unpack_from(f.fmt, buf, f.offset)[0]
+
+ Point = Message('Point', {'x': Field('l', 0),
+ 'y': Field('l', 8),
+ 'color': Field('i', 16)})
+
+ def main():
+ res = 0
+ for p in PLIST:
+ x = Point.read(p, 'x')
+ res += x
+ print res
+
+|end_example|
+|end_scriptsize|
+
+Example: better API
+----------------------------
+
+|scriptsize|
+|example<| |small| decode1.py trace (1) |end_small| |>|
+
+.. sourcecode:: python
+
+ debug_merge_point(1, 1, '<code object read> #34 CALL_METHOD')
+ p156 = getfield_gc_pure(p154, descr=<W_BytesObject.inst__value 8>)
+ i157 = getfield_gc_pure(p155, descr=<W_IntObject.inst_intval 8>)
+ p158 = new_with_vtable(-1228074336)
+ setfield_gc(p158, 0, descr=<CalcSizeFormatIterator.inst_totalsize 8>)
+ call(interpret_trampoline__v238___simple_call__function_i, p158, p156, ...)
+ guard_no_exception(descr=<Guard0xb3a8cd00>)
+ i159 = getfield_gc(p158, descr=<CalcSizeFormatIterator.inst_totalsize 8>)
+ i160 = int_lt(i157, 0)
+ guard_false(i160, descr=<Guard0xb3a8ccd0>)
+ i161 = strlen(p141)
+ i162 = int_sub(i161, i157)
+ i163 = int_lt(i162, i159)
+ guard_false(i163, descr=<Guard0xb3a8cca0>)
+ i164 = int_ge(i159, 0)
+ guard_true(i164, descr=<Guard0xb3a8cc70>)
+ p165 = force_token()
+ p166 = new_with_vtable(-1228077368)
+ p167 = new_with_vtable(-1228077280)
+ p168 = new_with_vtable(-1228267680)
+ setfield_gc(p167, 1, descr=<FieldU
rpython.rlib.buffer.Buffer.inst_readonly 8>)
+|end_example|
+|end_scriptsize|
+
+Example: better API
+----------------------------
+
+|scriptsize|
+|example<| |small| decode1.py trace (2) |end_small| |>|
+
+.. sourcecode:: python
+
+ p169 = new(descr=<SizeDescr 12>)
+ p170 = new_array_clear(0, descr=<ArrayP 4>)
+ p171 = new_with_vtable(-1229823908)
+ setfield_gc(p171, p145, descr=<JitVirtualRef.virtual_token 8>)
+ setfield_gc(p171, p145, descr=<JitVirtualRef.virtual_token 8>)
+ setfield_gc(p171, ConstPtr(null), descr=<FieldP JitVirtualRef.forced 12>)
+ setfield_gc(p51, p171, descr=<ExecutionContext.inst_topframeref 40>)
+ setfield_gc(p0, p165, descr=<PyFrame.vable_token 8>)
+ setfield_gc(p168, 1, descr=<Buffer.inst_readonly 8>)
+ setfield_gc(p168, p141, descr=<StringBuffer.inst_value 12>)
+ setfield_gc(p167, p168, descr=<SubBuffer.inst_buffer 12>)
+ setfield_gc(p167, i157, descr=<SubBuffer.inst_offset 16>)
+ setfield_gc(p167, i159, descr=<SubBuffer.inst_size 20>)
+ setfield_gc(p166, p167, descr=<UnpackFormatIterator.inst_buf 8>)
+ setfield_gc(p166, i159, descr=<UnpackFormatIterator.inst_length 12>)
+ setfield_gc(p166, 0, descr=<UnpackFormatIterator.inst_pos 16>)
+ setfield_gc(p169, 0, descr=<list.length 4>)
+ setfield_gc(p169, p170, descr=<list.items 8>)
+ setfield_gc(p166, p169, descr=<UnpackFormatIterator.inst_result_w 20>)
+
+|end_example|
+|end_scriptsize|
+
+
+Example: better API
+----------------------------
+
+|scriptsize|
+|example<| |small| decode1.py trace (3) |end_small| |>|
+
+.. sourcecode:: python
+
+ call_may_force(interpret_trampoline__v628___simple_call__function_i),
p166, p156, descr=<Callv 0 rr EF=6>)
+ guard_not_forced(descr=<Guard0xb3a8b9d0>)
+ guard_no_exception(descr=<Guard0xb3a8cc40>)
+ p172 = getfield_gc(p166, descr=<UnpackFormatIterator.inst_result_w 20>)
+ i173 = getfield_gc(p172, descr=<list.length 4>)
+ p174 = new_array_clear(i173, descr=<ArrayP 4>)
+ p175 = getfield_gc(p172, descr=<list.items 8>)
+ call(ll_arraycopy__arrayPtr_arrayPtr_Signed_Signed_Signed), p175, p174, 0,
0, i173, descr=<Callv 0 rriii EF=2 OS=1>)
+ i176 = int_eq(i173, 2)
+ guard_false(i176, descr=<Guard0xb3a8cc10>)
+
+|end_example|
+|end_scriptsize|
+
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