1 files changed, 38 insertions, 0 deletions
diff --git a/layout/style/ServoUtils.h b/layout/style/ServoUtils.h
new file mode 100644
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+++ b/layout/style/ServoUtils.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/* some utilities for Gecko to use for Servo initialization and assertions */
+
+#ifndef mozilla_ServoUtils_h
+#define mozilla_ServoUtils_h
+
+#include "mozilla/Assertions.h"
+#include "MainThreadUtils.h"
+
+namespace mozilla {
+
+// Defined in GeckoBindings.cpp.
+void InitializeServo();
+void ShutdownServo();
+void AssertIsMainThreadOrServoFontMetricsLocked();
+
+class ServoStyleSet;
+extern ServoStyleSet* sInServoTraversal;
+inline bool IsInServoTraversal() {
+  // The callers of this function are generally main-thread-only _except_
+  // for potentially running during the Servo traversal, in which case they may
+  // take special paths that avoid writing to caches and the like. In order
+  // to allow those callers to branch efficiently without checking TLS, we
+  // maintain this static boolean. However, the danger is that those callers
+  // are generally unprepared to deal with non-Servo-but-also-non-main-thread
+  // callers, and are likely to take the main-thread codepath if this function
+  // returns false. So we assert against other non-main-thread callers here.
+  MOZ_ASSERT(sInServoTraversal || NS_IsMainThread());
+  return sInServoTraversal;
+}
+}  // namespace mozilla
+
+#endif  // mozilla_ServoUtils_h