[smg][ci] Add thread safety to ModelPool and GPUAllocator (#16674)

sgl-model-gateway/e2e_test/pyproject.toml

@@ -9,7 +9,9 @@ dependencies = [
   "grpcio-health-checking",
   "httpx",
   "openai",
+  "py",  # Required for pytest-parallel with newer pytest versions
   "pytest",
+  "pytest-parallel",
   "pytest-rerunfailures",
 ]
 
@@ -23,8 +25,20 @@ testpaths = ["."]
 markers = [
   "e2e: mark test as end-to-end test requiring GPU workers",
   "slow: mark test as slow-running",
+  "thread_unsafe: mark test as incompatible with parallel thread execution",
 ]
 addopts = "-v -s"
 # Explicitly disable live log to avoid "---- live log ----" dividers
 # We configure logging manually in conftest.py
 log_cli = false
+
+# Parallel execution configuration:
+# Use --workers 1 --tests-per-worker N to run N tests concurrently as threads
+# within a single process. This enables true shared-worker parallelism where
+# the session-scoped model_pool fixture is shared across all threads.
+#
+# Example usage:
+#   pytest --workers 1 --tests-per-worker 4 e2e_test/router/
+#
+# The thread-safe ModelPool and GPUAllocator classes enable safe concurrent
+# access from multiple test threads.