1 files changed, 226 insertions, 0 deletions
diff --git a/js/src/vm/SharedMem.h b/js/src/vm/SharedMem.h
new file mode 100644
index 000000000..f30bf99e8
--- /dev/null
+++ b/js/src/vm/SharedMem.h
@@ -0,0 +1,226 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * 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/. */
+
+#ifndef vm_SharedMem_h
+#define vm_SharedMem_h
+
+#include "mozilla/TypeTraits.h"
+
+template<typename T>
+class SharedMem
+{
+    static_assert(mozilla::IsPointer<T>::value,
+                  "SharedMem encapsulates pointer types");
+
+    enum Sharedness {
+        IsUnshared,
+        IsShared
+    };
+
+    T ptr_;
+#ifdef DEBUG
+    Sharedness sharedness_;
+#endif
+
+    SharedMem(T ptr, Sharedness sharedness)
+      : ptr_(ptr)
+#ifdef DEBUG
+      , sharedness_(sharedness)
+#endif
+    {}
+
+  public:
+    // Create a SharedMem<T> that is an unshared nullptr.
+    SharedMem()
+      : ptr_(nullptr)
+#ifdef DEBUG
+      , sharedness_(IsUnshared)
+#endif
+    {}
+
+    // Create a SharedMem<T> that's shared/unshared in the same way as
+    // "forSharedness".
+    SharedMem(T ptr, const SharedMem& forSharedness)
+      : ptr_(ptr)
+#ifdef DEBUG
+      , sharedness_(forSharedness.sharedness_)
+#endif
+    {}
+
+    // Create a SharedMem<T> that's marked as shared.
+    static SharedMem shared(void* p) {
+        return SharedMem(static_cast<T>(p), IsShared);
+    }
+
+    // Create a SharedMem<T> that's marked as unshared.
+    static SharedMem unshared(void* p) {
+        return SharedMem(static_cast<T>(p), IsUnshared);
+    }
+
+    SharedMem& operator =(const SharedMem& that) {
+        ptr_ = that.ptr_;
+#ifdef DEBUG
+        sharedness_ = that.sharedness_;
+#endif
+        return *this;
+    }
+
+    // Reinterpret-cast the pointer to type U, preserving sharedness.
+    template<typename U>
+    inline SharedMem<U> cast() const {
+#ifdef DEBUG
+        MOZ_ASSERT(asValue() % sizeof(mozilla::Conditional<mozilla::IsVoid<typename mozilla::RemovePointer<U>::Type>::value,
+                                                           char,
+                                                           typename mozilla::RemovePointer<U>::Type>) == 0);
+        if (sharedness_ == IsUnshared)
+            return SharedMem<U>::unshared(unwrap());
+#endif
+        return SharedMem<U>::shared(unwrap());
+    }
+
+    explicit operator bool() { return ptr_ != nullptr; }
+
+    SharedMem operator +(size_t offset) {
+        return SharedMem(ptr_ + offset, *this);
+    }
+
+    SharedMem operator -(size_t offset) {
+        return SharedMem(ptr_ - offset, *this);
+    }
+
+    SharedMem operator ++() {
+        ptr_++;
+        return *this;
+    }
+
+    SharedMem operator ++(int) {
+        SharedMem<T> result(*this);
+        ptr_++;
+        return result;
+    }
+
+    SharedMem operator --() {
+        ptr_--;
+        return *this;
+    }
+
+    SharedMem operator --(int) {
+        SharedMem<T> result(*this);
+        ptr_--;
+        return result;
+    }
+
+    uintptr_t asValue() const {
+        return reinterpret_cast<uintptr_t>(ptr_);
+    }
+
+    // Cast to char*, add nbytes, and cast back to T.  Simplifies code in a few places.
+    SharedMem addBytes(size_t nbytes) {
+        MOZ_ASSERT(nbytes % sizeof(mozilla::Conditional<mozilla::IsVoid<typename mozilla::RemovePointer<T>::Type>::value,
+                                                        char,
+                                                        typename mozilla::RemovePointer<T>::Type>) == 0);
+        return SharedMem(reinterpret_cast<T>(reinterpret_cast<char*>(ptr_) + nbytes), *this);
+    }
+
+    T unwrap() const {
+        return ptr_;
+    }
+
+    T unwrapUnshared() const {
+        MOZ_ASSERT(sharedness_ == IsUnshared);
+        return ptr_;
+    }
+
+    uintptr_t unwrapValue() const {
+        return reinterpret_cast<uintptr_t>(ptr_);
+    }
+};
+
+template<typename T>
+inline bool
+operator >=(const SharedMem<T>& a, const SharedMem<T>& b)
+{
+    return a.unwrap() >= b.unwrap();
+}
+
+template<typename T>
+inline bool
+operator >=(const void* a, const SharedMem<T>& b)
+{
+    return a >= b.unwrap();
+}
+
+template<typename T>
+inline bool
+operator ==(const void* a, const SharedMem<T>& b)
+{
+    return a == b.unwrap();
+}
+
+template<typename T>
+inline bool
+operator ==(const SharedMem<T>& a, decltype(nullptr) b)
+{
+    return a.unwrap() == b;
+}
+
+template<typename T>
+inline bool
+operator ==(const SharedMem<T>& a, const SharedMem<T>& b)
+{
+    return a.unwrap() == b.unwrap();
+}
+
+template<typename T>
+inline bool
+operator !=(const SharedMem<T>& a, decltype(nullptr) b)
+{
+    return a.unwrap() != b;
+}
+
+template<typename T>
+inline bool
+operator !=(const SharedMem<T>& a, const SharedMem<T>& b)
+{
+    return a.unwrap() != b.unwrap();
+}
+
+template<typename T>
+inline bool
+operator >(const SharedMem<T>& a, const SharedMem<T>& b)
+{
+    return a.unwrap() > b.unwrap();
+}
+
+template<typename T>
+inline bool
+operator >(const void* a, const SharedMem<T>& b)
+{
+    return a > b.unwrap();
+}
+
+template<typename T>
+inline bool
+operator <=(const SharedMem<T>& a, const SharedMem<T>& b)
+{
+    return a.unwrap() <= b.unwrap();
+}
+
+template<typename T>
+inline bool
+operator <=(const void* a, const SharedMem<T>& b)
+{
+    return a <= b.unwrap();
+}
+
+template<typename T>
+inline bool
+operator <(const void* a, const SharedMem<T>& b)
+{
+    return a < b.unwrap();
+}
+
+#endif // vm_SharedMem_h