Change X11 error handler override to allow easy X11 error checking.

ui/base/x/x11_util.cc

Index: ui/base/x/x11_util.cc
diff --git a/ui/base/x/x11_util.cc b/ui/base/x/x11_util.cc
index 39c2cff7c6f098fd1a951ce4113924f20b23bc70..0dd6e9c618db8793cf3ef12a7e1891de81503509 100644
--- a/ui/base/x/x11_util.cc
+++ b/ui/base/x/x11_util.cc
@@ -65,6 +65,8 @@ CachedPictFormats* get_cached_pict_formats() {
 const size_t kMaxCacheSize = 5;
 
 int DefaultX11ErrorHandler(Display* d, XErrorEvent* e) {
+  DCHECK(!MessageLoop::current() ||
+         MessageLoop::current()->type() == MessageLoop::TYPE_UI);
   MessageLoop::current()->PostTask(
        FROM_HERE, NewRunnableFunction(LogErrorEventDescription, d, *e));
   return 0;
@@ -76,6 +78,14 @@ int DefaultX11IOErrorHandler(Display* d) {
   _exit(1);
 }
 
+XErrorHandler current_error_handler = DefaultX11ErrorHandler;
+XErrorEvent last_error_event = {0, NULL, 0, 0, 0, 0, 0 };
+
+int BaseX11ErrorHandler(Display* d, XErrorEvent* e) {
+  last_error_event = *e;
+  return current_error_handler(d, e);
+}
+
 Atom GetAtom(const char* name) {
 #if defined(TOOLKIT_USES_GTK)
   return gdk_x11_get_xatom_by_name_for_display(
@@ -105,6 +115,49 @@ bool GetProperty(XID window, const std::string& property_name, long max_length,
                             property);
 }
 
+std::string BuildX11ErrorString(const XErrorEvent& error_event) {
+  char error_str[256];
+  char request_str[256];
+
+  XGetErrorText(error_event.display, error_event.error_code, error_str,
+                sizeof(error_str));
+
+  strncpy(request_str, "Unknown", sizeof(request_str));
+  if (error_event.request_code < 128) {
+    std::string num = base::UintToString(error_event.request_code);
+    XGetErrorDatabaseText(error_event.display, "XRequest", num.c_str(),
+                          "Unknown", request_str, sizeof(request_str));
+  } else {
+    int num_ext;
+    char** ext_list = XListExtensions(error_event.display, &num_ext);
+
+    for (int i = 0; i < num_ext; i++) {
+      int ext_code, first_event, first_error;
+      XQueryExtension(error_event.display, ext_list[i], &ext_code, &first_event,
+                      &first_error);
+      if (error_event.request_code == ext_code) {
+        std::string msg = StringPrintf(
+            "%s.%d", ext_list[i], error_event.minor_code);
+        XGetErrorDatabaseText(error_event.display, "XRequest", msg.c_str(),
+                              "Unknown", request_str, sizeof(request_str));
+        break;
+      }
+    }
+    XFreeExtensionList(ext_list);
+  }
+
+  std::ostringstream error_ss;
+  error_ss << "X Error detected: "
+           << "serial " << error_event.serial << ", "
+           << "error_code " << static_cast<int>(error_event.error_code)
+           << " (" << error_str << "), "
+           << "request_code " << static_cast<int>(error_event.request_code)
+           << ", "
+           << "minor_code " << static_cast<int>(error_event.minor_code)
+           << " (" << request_str << ")";
+  return error_ss.str();
+}
+
 }  // namespace
 
 bool XDisplayExists() {
@@ -695,6 +748,7 @@ bool ChangeWindowDesktop(XID window, XID destination) {
 }
 
 void SetDefaultX11ErrorHandlers() {
+  XSetErrorHandler(BaseX11ErrorHandler);
   SetX11ErrorHandlers(NULL, NULL);
 }
 
@@ -730,6 +784,15 @@ bool IsX11WindowFullScreen(XID window) {
 #endif
 }
 
+void CheckForReportedX11Error() {
+  DCHECK(!MessageLoop::current() ||
+         MessageLoop::current()->type() == MessageLoop::TYPE_UI);
+  if (!last_error_event.display)
+    return;
+  XSync(last_error_event.display, False);
+  LOG(FATAL) << BuildX11ErrorString(last_error_event);
+}
+
 // ----------------------------------------------------------------------------
 // These functions are declared in x11_util_internal.h because they require
 // XLib.h to be included, and it conflicts with many other headers.
@@ -808,51 +871,21 @@ XRenderPictFormat* GetRenderVisualFormat(Display* dpy, Visual* visual) {
 
 void SetX11ErrorHandlers(XErrorHandler error_handler,
                          XIOErrorHandler io_error_handler) {
-  XSetErrorHandler(error_handler ? error_handler : DefaultX11ErrorHandler);
-  XSetIOErrorHandler(
-      io_error_handler ? io_error_handler : DefaultX11IOErrorHandler);
+  DCHECK(!MessageLoop::current() ||
+         MessageLoop::current()->type() == MessageLoop::TYPE_UI);
+  current_error_handler = error_handler ?
+      error_handler : DefaultX11ErrorHandler;
+  XSetIOErrorHandler(io_error_handler ?
+                     io_error_handler : DefaultX11IOErrorHandler);
 }
 
 void LogErrorEventDescription(Display* dpy,
                               const XErrorEvent& error_event) {
-  char error_str[256];
-  char request_str[256];
-
-  XGetErrorText(dpy, error_event.error_code, error_str, sizeof(error_str));
-
-  strncpy(request_str, "Unknown", sizeof(request_str));
-  if (error_event.request_code < 128) {
-    std::string num = base::UintToString(error_event.request_code);
-    XGetErrorDatabaseText(
-        dpy, "XRequest", num.c_str(), "Unknown", request_str,
-        sizeof(request_str));
-  } else {
-    int num_ext;
-    char** ext_list = XListExtensions(dpy, &num_ext);
-
-    for (int i = 0; i < num_ext; i++) {
-      int ext_code, first_event, first_error;
-      XQueryExtension(dpy, ext_list[i], &ext_code, &first_event, &first_error);
-      if (error_event.request_code == ext_code) {
-        std::string msg = StringPrintf(
-            "%s.%d", ext_list[i], error_event.minor_code);
-        XGetErrorDatabaseText(
-            dpy, "XRequest", msg.c_str(), "Unknown", request_str,
-            sizeof(request_str));
-        break;
-      }
-    }
-    XFreeExtensionList(ext_list);
-  }
-
-  LOG(ERROR) 
-      << "X Error detected: "
-      << "serial " << error_event.serial << ", "
-      << "error_code " << static_cast<int>(error_event.error_code)
-      << " (" << error_str << "), "
-      << "request_code " << static_cast<int>(error_event.request_code) << ", "
-      << "minor_code " << static_cast<int>(error_event.minor_code)
-      << " (" << request_str << ")";
+  DCHECK(!MessageLoop::current() ||
+         MessageLoop::current()->type() == MessageLoop::TYPE_UI);
+  DCHECK_EQ(dpy, error_event.display)
+      << "Attempt to log error for mismatching X11 display.";
+  LOG(ERROR) << BuildX11ErrorString(error_event);
 }
 
 // ----------------------------------------------------------------------------