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-rw-r--r--js/src/vm/SharedMem.h208
1 files changed, 208 insertions, 0 deletions
diff --git a/js/src/vm/SharedMem.h b/js/src/vm/SharedMem.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/. */
+
+#ifndef vm_SharedMem_h
+#define vm_SharedMem_h
+
+#include "mozilla/Assertions.h"
+
+#include <type_traits>
+
+template <typename T>
+class SharedMem {
+ static_assert(std::is_pointer_v<T>, "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.
+ // Eg, "obj->dataPointerEither().cast<uint8_t*>()" yields a
+ // SharedMem<uint8_t*>.
+ template <typename U>
+ inline SharedMem<U> cast() const {
+#ifdef DEBUG
+ MOZ_ASSERT(
+ asValue() %
+ sizeof(std::conditional_t<std::is_void_v<std::remove_pointer_t<U>>,
+ char, std::remove_pointer_t<U>>) ==
+ 0);
+ if (sharedness_ == IsUnshared) {
+ return SharedMem<U>::unshared(unwrap());
+ }
+#endif
+ return SharedMem<U>::shared(unwrap());
+ }
+
+ explicit operator bool() const { return ptr_ != nullptr; }
+
+ SharedMem operator+(size_t offset) const {
+ return SharedMem(ptr_ + offset, *this);
+ }
+
+ SharedMem operator-(size_t offset) const {
+ 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(std::conditional_t<std::is_void_v<std::remove_pointer_t<T>>,
+ char, std::remove_pointer_t<T>>) ==
+ 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