webkitgtk-2.16.5HEADwebkitgtk-2.16.5master

1 files changed, 118 insertions, 0 deletions

diff --git a/Source/JavaScriptCore/runtime/LazyProperty.h b/Source/JavaScriptCore/runtime/LazyProperty.h
new file mode 100644
index 000000000..169f202b2
--- /dev/null
+++ b/Source/JavaScriptCore/runtime/LazyProperty.h
@@ -0,0 +1,118 @@
+/*
+ * Copyright (C) 2016 Apple Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
+ * THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include "VM.h"
+
+namespace JSC {
+
+class JSCell;
+class SlotVisitor;
+class VM;
+
+// Note that if all you're doing is calling LazyProperty::get(), it's completely safe to bitcast
+// this LazyProperty<JSCell, JSCell>.
+template<typename OwnerType, typename ElementType>
+class LazyProperty {
+public:
+    struct Initializer {
+        Initializer(OwnerType* owner, LazyProperty& property)
+            : vm(*Heap::heap(owner)->vm())
+            , owner(owner)
+            , property(property)
+        {
+        }
+        
+        void set(ElementType* value) const;
+
+        VM& vm;
+        OwnerType* owner;
+        LazyProperty& property;
+    };
+
+private:
+    typedef ElementType* (*FuncType)(const Initializer&);
+
+public:
+    LazyProperty()
+    {
+    }
+
+    // Tell the property to run the given callback next time someone tries to get the value
+    // using get(). The passed callback must be stateless. For example:
+    //
+    //     property.initLater(
+    //         [] (const LazyProperty<Foo, Bar>::Initializer& init) {
+    //             init.set(...things...);
+    //         });
+    //
+    // This method is always inlineable and should always compile to a store of a constant
+    // pointer no matter how complicated the callback is.
+    template<typename Func>
+    void initLater(const Func&);
+
+    // This lazily initializes the property. Note that this gracefully supports recursive calls.
+    // If this gets called while the property is being initialized, it will simply return null.
+    ElementType* get(const OwnerType* owner) const
+    {
+        ASSERT(!isCompilationThread());
+        if (UNLIKELY(m_pointer & lazyTag)) {
+            FuncType func = *bitwise_cast<FuncType*>(m_pointer & ~(lazyTag | initializingTag));
+            return func(Initializer(const_cast<OwnerType*>(owner), *const_cast<LazyProperty*>(this)));
+        }
+        return bitwise_cast<ElementType*>(m_pointer);
+    }
+    
+    ElementType* getConcurrently() const
+    {
+        uintptr_t pointer = m_pointer;
+        if (pointer & lazyTag)
+            return nullptr;
+        return bitwise_cast<ElementType*>(pointer);
+    }
+    
+    void setMayBeNull(VM&, const OwnerType* owner, ElementType*);
+    void set(VM&, const OwnerType* owner, ElementType*);
+    
+    void visit(SlotVisitor&);
+    
+    void dump(PrintStream&) const;
+    
+private:
+    template<typename Func>
+    static ElementType* callFunc(const Initializer&);
+    
+    static const uintptr_t lazyTag = 1;
+    static const uintptr_t initializingTag = 2;
+    
+    uintptr_t m_pointer { 0 };
+};
+
+// It's valid to bitcast any LazyProperty to LazyCellProperty if you're just going to call get()
+// or getConcurrently().
+typedef LazyProperty<JSCell, JSCell> LazyCellProperty;
+
+} // namespace JSC