EnvField.get() re-read os.environ (os.getenv + parse) on every call. The
attention/compose hot path reads many flags per layer / per compose
(nsa_backend ~11/layer, cp_shared_kv_runtime ~12/compose) -- thousands of
os.getenv + Python-method calls per forward for values that are fixed startup
config.
Cache the parsed value on first read; invalidate on every mutation through the
API (set / override / clear). The only env vars mutated at runtime to pass
information are NOT EnvFields (SGLANG_TMP_NCCL_COMM_VALUE is read by C getenv;
SGLANG_RUN_ID / SGLANG_DP_RANK via raw os.environ), so the cache does not affect
them. Convert the two direct os.environ["SGLANG_*"]=... writes in server_args
(SGLANG_VLM_CACHE_SIZE_MB, SGLANG_ENABLE_DETERMINISTIC_INFERENCE) to envs.X.set()
so they invalidate the cache.
Verified: cache + set/override/clear invalidation behavioral test passes;
331 mem_cache/parser/layers unit tests pass (5 pre-existing CUDA-device-assert
failures unrelated).
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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