[mypyc] Create function wrappers of nested coroutines lazily - #22048
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Each instance of a nested async def's callable class used to get its own CPyFunction wrapper at instantiation. Creating it allocates a method def, a code object, a name string and the function object, which made defining a nested async def several times slower than calling it. The wrapper is only used for introspection (__name__, __code__, __defaults__, etc.), so create it on first access in the property getters and setters instead. Microbenchmark (separate=True, Python 3.14, arm64 macOS; ns per call of an outer coroutine that defines and awaits a nested async def): before 259.6 after 69.6 In production profiles of a large async service, CPyFunction_New and the wrapper's dealloc were ~0.16% of CPU.
Creating the wrapper may run arbitrary code (e.g. via GC) that could have initialized the attribute already, so only store it if still NULL.
p-sawicki
approved these changes
Sep 25, 2026
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Each nested async def instance used to get it's own freshly allocated
function wrapper object, which is only needed relatively rarely for
introspection (e.g.
__name__). This was slow to construct. Now weconstruct this lazily. On free-threaded builds we need to deal with
other threads racing as well.
Top-level coroutines and methods are unaffected. Their wrappers were
already created once at import time.
Microbenchmark results (Python 3.14, 1M iterations):