gh-112278: Improve error handling in wmi module and tests (GH-117818)

Lib/test/test_wmi.py

@@ -14,6 +14,8 @@ def wmi_exec_query(query):
     # gh-112278: WMI maybe slow response when first call.
     try:
         return _wmi.exec_query(query)
+    except BrokenPipeError:
+        pass
     except WindowsError as e:
         if e.winerror != 258:
             raise

PC/_wmimodule.cpp

@@ -279,10 +279,12 @@ _wmi_exec_query_impl(PyObject *module, PyObject *query)
     // a timeout.  The initEvent will be set after COM initialization, it will
     // take a longer time when first initialized.  The connectEvent will be set
     // after connected to WMI.
+    if (!err) {
         err = wait_event(data.initEvent, 1000);
         if (!err) {
             err = wait_event(data.connectEvent, 100);
         }
+    }
 
     while (!err) {
         if (ReadFile(
@@ -305,28 +307,33 @@ _wmi_exec_query_impl(PyObject *module, PyObject *query)
         CloseHandle(data.readPipe);
     }
 
+    if (hThread) {
         // Allow the thread some time to clean up
+        int thread_err;
         switch (WaitForSingleObject(hThread, 100)) {
         case WAIT_OBJECT_0:
             // Thread ended cleanly
-        if (!GetExitCodeThread(hThread, (LPDWORD)&err)) {
-            err = GetLastError();
+            if (!GetExitCodeThread(hThread, (LPDWORD)&thread_err)) {
+                thread_err = GetLastError();
             }
             break;
         case WAIT_TIMEOUT:
             // Probably stuck - there's not much we can do, unfortunately
-        if (err == 0 || err == ERROR_BROKEN_PIPE) {
-            err = WAIT_TIMEOUT;
-        }
+            thread_err = WAIT_TIMEOUT;
             break;
         default:
-        if (err == 0 || err == ERROR_BROKEN_PIPE) {
-            err = GetLastError();
-        }
+            thread_err = GetLastError();
             break;
         }
+        // An error on our side is more likely to be relevant than one from
+        // the thread, but if we don't have one on our side we'll take theirs.
+        if (err == 0 || err == ERROR_BROKEN_PIPE) {
+            err = thread_err;
+        }
 
         CloseHandle(hThread);
+    }
+
     CloseHandle(data.initEvent);
     CloseHandle(data.connectEvent);
     hThread = NULL;