Sync from v0.13

csrc/core/batch_invariant.hpp

@@ -0,0 +1,19 @@
+#pragma once
+#include <cstdlib>
+#include <string>
+#include <cctype>
+
+namespace vllm {
+
+// vllm_is_batch_invariant(); returns true
+// if env VLLM_BATCH_INVARIANT=1
+inline bool vllm_is_batch_invariant() {
+  static bool cached = []() {
+    std::string env_key = "VLLM_BATCH_INVARIANT";
+    const char* val = std::getenv(env_key.c_str());
+    return (val && std::atoi(val) != 0) ? 1 : 0;
+  }();
+  return cached;
+}
+
+}  // namespace vllm