52abd47f8c
### What this PR does / why we need it? This PR aims to remove env introduced by #3988 and use lock by default. As described in https://github.com/vllm-project/vllm/issues/27858, we have tested the writer lock method in various scenarios and the performance is almost unaffected. Therefore, we believe that it would be safe to enable the lock by default and remove the redundant env `SHM_BARRIER` now. After discussion, we decide to preserve env and set it as true by default. ### Does this PR introduce _any_ user-facing change? `SHM_BARRIER` is set as true by default. ### How was this patch tested? by ci --------- Signed-off-by: Zetong Li <slippersss@126.com>