test

Author: felixweinberger

src/mcp/os/win32/utilities.py

@@ -184,6 +184,14 @@ async def create_windows_process(
     Returns:
         Process | FallbackProcess: Async-compatible subprocess with stdin and stdout streams
     """
+    # Log event loop information for debugging CI behavior
+    try:
+        import asyncio
+        loop = asyncio.get_running_loop()
+        logger.info(f"Windows process creation - Event loop: {loop.__class__.__name__} from {loop.__class__.__module__}")
+    except Exception:
+        pass  # Don't fail if we can't get loop info
+    
     job = _create_job_object()
     process = None
 
@@ -199,11 +207,15 @@ async def create_windows_process(
             stderr=errlog,
             cwd=cwd,
         )
-    except NotImplementedError:
+    except NotImplementedError as e:
         # If Windows doesn't support async subprocess creation, use fallback
+        logger.warning(f"anyio.open_process raised NotImplementedError: {e}")
+        logger.warning("Using FallbackProcess (likely SelectorEventLoop on Windows)")
         process = await _create_windows_fallback_process(command, args, env, errlog, cwd)
-    except Exception:
+    except Exception as e:
         # Try again without creation flags
+        logger.info(f"anyio.open_process failed with {type(e).__name__}: {e}")
+        logger.info("Retrying without creation flags")
         process = await anyio.open_process(
             [command, *args],
             env=env,
@@ -212,6 +224,11 @@ async def create_windows_process(
         )
 
     _maybe_assign_process_to_job(process, job)
+    
+    # Log which type of process was created
+    process_type = type(process).__name__
+    logger.info(f"Created process type: {process_type} (pid: {process.pid})")
+    
     return process
 
 

tests/issues/test_1027_win_unreachable_cleanup.py

@@ -8,6 +8,8 @@
 These tests verify the fix continues to work correctly across all platforms.
 """
 
+import platform
+
 import asyncio
 import sys
 import tempfile
@@ -21,6 +23,45 @@
 from mcp.client.stdio import _create_platform_compatible_process, stdio_client
 
 
+def _get_event_loop_info():
+    """Get information about the current event loop for debugging."""
+    try:
+        loop = asyncio.get_running_loop()
+        return {
+            "class": loop.__class__.__name__,
+            "module": loop.__class__.__module__,
+            "is_proactor": "Proactor" in loop.__class__.__name__,
+            "is_selector": "Selector" in loop.__class__.__name__,
+        }
+    except RuntimeError:
+        return {"error": "No running event loop"}
+
+
+@pytest.mark.anyio
+@pytest.mark.skipif(sys.platform != "win32", reason="Windows-specific event loop detection")
+async def test_windows_event_loop_detection():
+    """Test to detect which event loop is being used on Windows CI."""
+    loop_info = _get_event_loop_info()
+    
+    # Print diagnostic info that will appear in CI logs
+    print(f"\n{'='*60}")
+    print("WINDOWS CI EVENT LOOP DIAGNOSTICS")
+    print(f"{'='*60}")
+    print(f"Python Version: {sys.version}")
+    print(f"Platform: {platform.platform()}")
+    print(f"Event Loop Class: {loop_info.get('class', 'Unknown')}")
+    print(f"Event Loop Module: {loop_info.get('module', 'Unknown')}")
+    print(f"Is ProactorEventLoop: {loop_info.get('is_proactor', False)}")
+    print(f"Is SelectorEventLoop: {loop_info.get('is_selector', False)}")
+    print(f"{'='*60}")
+    print("ProactorEventLoop = Supports subprocesses (default since Python 3.8)")
+    print("SelectorEventLoop = Does NOT support subprocesses (uses FallbackProcess)")
+    print(f"{'='*60}\n")
+    
+    # Intentionally fail to ensure output appears in CI logs
+    pytest.fail("DIAGNOSTIC TEST - Intentionally failing to show event loop info in CI")
+
+
 @pytest.mark.anyio
 async def test_lifespan_cleanup_executed():
     """
@@ -195,9 +236,19 @@ def echo(text: str) -> str:
     try:
         # This test manually manages the process to verify stdin-based shutdown
         # Start the server process
+        if sys.platform == "win32":
+            # Force output to stderr which is captured even with xdist
+            import sys as sys_module
+            print(f"\n[WINDOWS DIAGNOSTICS] Event loop: {_get_event_loop_info()}", file=sys_module.stderr)
+            print(f"[WINDOWS DIAGNOSTICS] About to create process...", file=sys_module.stderr)
+            
         process = await _create_platform_compatible_process(
             command=sys.executable, args=[server_script], env=None, errlog=sys.stderr, cwd=None
         )
+        
+        if sys.platform == "win32":
+            print(f"[WINDOWS DIAGNOSTICS] Created process type: {type(process).__name__}", file=sys_module.stderr)
+            print(f"[WINDOWS DIAGNOSTICS] Has returncode: {hasattr(process, 'returncode')}", file=sys_module.stderr)
 
         # Wait for server to start
         await asyncio.sleep(1.0)  # Give more time on Windows