New submission from Vladimir Matveev <[email protected]>:
Currently async functions are more expensive to use comparing to their sync
counterparts. A simple microbenchmark shows that difference could be quite
significant:
```
import time
def f(a):
if a == 0:
return 0
return f(a - 1)
async def g(a):
if a == 0:
return 0
return await g(a - 1)
N = 100000
C = 200
t0 = time.time()
for _ in range(N):
f(C)
t1 = time.time()
for _ in range(N):
try:
g(C).send(None)
except StopIteration:
pass
t2 = time.time()
print(f"Sync functions: {t1 - t0} s")
print(f"Coroutines: {t2 - t1} s")
```
Results from master on my machine:
Sync functions: 2.8642687797546387 s
Coroutines: 9.172159910202026 s
NOTE: Due to viral nature of async functions their number in codebase could
become quite significant so having hundreds of them in a single call stack is
not something uncommon.
One of reasons of such performance gap is that async functions always return
its results via raising StopIteration exception which is not cheap. This can be
avoided if in addition to `_PyGen_Send` always return result via exception we
could have another function that will allow us to distinguish whether value
that was returned from generator is a final result (return case) of whether
this is yielded value.
In linked PR I've added function `_PyGen_SendNoStopIteration` with this
behavior and updated ceval.c and _asynciomodule.c to use it instead of
`_PyGen_Send` which resulted in a measurable difference:
Sync functions: 2.8861589431762695 s
Coroutines: 5.730362176895142 s
----------
messages: 376698
nosy: v2m, yselivanov
priority: normal
severity: normal
status: open
title: Do not always use exceptions to return result from coroutine
type: performance
versions: Python 3.10
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Python tracker <[email protected]>
<https://bugs.python.org/issue41756>
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