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Ensure writable frames #3967

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merged 13 commits into from
Jul 17, 2020
Merged

Ensure writable frames #3967

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8fac8bc
Test NumPy array is writable after serialization
jakirkham Jul 17, 2020
50808a1
Parametrize `merge_frames` tests
jakirkham Jul 17, 2020
1077ce6
Test splitting large frame into pieces
jakirkham Jul 17, 2020
4c6d589
Test joining smaller frames together
jakirkham Jul 17, 2020
b4297ac
Add an extra equally sized frame for good measure
jakirkham Jul 17, 2020
8457257
Test all frames are `memoryview`s
jakirkham Jul 17, 2020
2fb24e5
Test all frames are writable
jakirkham Jul 17, 2020
52b9aec
Coerce all frames to `memoryview`s
jakirkham Jul 17, 2020
de23315
Guard against more complex handling
jakirkham Jul 17, 2020
565ce49
Just use append with singleton list
jakirkham Jul 17, 2020
ac8b40e
Create empty `bytes` object explicitly
jakirkham Jul 17, 2020
ee93917
Use `bytearray`s to join frames
jakirkham Jul 17, 2020
859fd3b
Ensure all frames are writable before returning
jakirkham Jul 17, 2020
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8 changes: 8 additions & 0 deletions distributed/protocol/tests/test_numpy.py
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Original file line number Diff line number Diff line change
Expand Up @@ -100,6 +100,14 @@ def test_dumps_serialize_numpy(x):
np.testing.assert_equal(x, y)


def test_dumps_numpy_writable():
a1 = np.arange(1000)
a1.flags.writeable = False
(a2,) = loads(dumps([to_serialize(a1)]))
assert (a1 == a2).all()
assert a2.flags.writeable


@pytest.mark.parametrize(
"x",
[
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34 changes: 24 additions & 10 deletions distributed/protocol/tests/test_protocol_utils.py
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Original file line number Diff line number Diff line change
@@ -1,19 +1,33 @@
import pytest

from distributed.protocol.utils import merge_frames, pack_frames, unpack_frames
from distributed.utils import ensure_bytes


def test_merge_frames():
result = merge_frames({"lengths": [3, 4]}, [b"12", b"34", b"567"])
expected = [b"123", b"4567"]

@pytest.mark.parametrize(
"lengths,frames",
[
([3], [b"123"]),
([3, 3], [b"123", b"456"]),
([2, 3, 2], [b"12345", b"67"]),
([5, 2], [b"123", b"45", b"67"]),
([3, 4], [b"12", b"34", b"567"]),
],
)
def test_merge_frames(lengths, frames):
header = {"lengths": lengths}
result = merge_frames(header, frames)

data = b"".join(frames)
expected = []
for i in lengths:
expected.append(data[:i])
data = data[i:]

assert all(isinstance(f, memoryview) for f in result)
assert all(not f.readonly for f in result)
assert list(map(ensure_bytes, result)) == expected

b = b"123"
assert merge_frames({"lengths": [3]}, [b])[0] is b

L = [b"123", b"456"]
assert merge_frames({"lengths": [3, 3]}, L) is L


def test_pack_frames():
frames = [b"123", b"asdf"]
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50 changes: 26 additions & 24 deletions distributed/protocol/utils.py
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Original file line number Diff line number Diff line change
Expand Up @@ -58,34 +58,36 @@ def merge_frames(header, frames):
[b'123456']
"""
lengths = list(header["lengths"])
frames = list(map(memoryview, frames))

assert sum(lengths) == sum(map(nbytes, frames))

if all(len(f) == l for f, l in zip(frames, lengths)):
return frames

frames = frames[::-1]
lengths = lengths[::-1]

out = []
while lengths:
l = lengths.pop()
L = []
while l:
frame = frames.pop()
if nbytes(frame) <= l:
L.append(frame)
l -= nbytes(frame)
if not all(len(f) == l for f, l in zip(frames, lengths)):
frames = frames[::-1]
lengths = lengths[::-1]

out = []
while lengths:
l = lengths.pop()
L = []
while l:
frame = frames.pop()
if nbytes(frame) <= l:
L.append(frame)
l -= nbytes(frame)
else:
L.append(frame[:l])
frames.append(frame[l:])
l = 0
if len(L) == 1: # no work necessary
out.append(L[0])
else:
mv = memoryview(frame)
L.append(mv[:l])
frames.append(mv[l:])
l = 0
if len(L) == 1: # no work necessary
out.extend(L)
else:
out.append(b"".join(L))
return out
out.append(memoryview(bytearray().join(L)))
frames = out

frames = [memoryview(bytearray(f)) if f.readonly else f for f in frames]
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For fun I decided to micro-benchmark this:

In [1]: L = [b'0' * i for i in [10, 100, 10, 100, 1000] * 2]                                                                                                                                                      

In [2]: %timeit b"".join(L)                                                                                                                                                                                       
203 ns ± 1.6 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)

In [3]: %timeit memoryview(bytearray().join(L))                                                                                                                                                                   
463 ns ± 5.9 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)

260ns doesn't really matter today I don't think


return frames


def pack_frames_prelude(frames):
Expand Down