Implements remaining SecurityContext calls for iOS

runtime/bin/reference_counting.h

+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+#ifndef BIN_REFERENCE_COUNTING_H_
+#define BIN_REFERENCE_COUNTING_H_
+
+#include "vm/atomic.h"
+
+namespace dart {
+namespace bin {
+
+// Forward declaration.
+template <class Target> class RefCntReleaseScope;
+
+// Inherit from this class where instances of the derived class should be
+// reference counted. Reference counts on instances are incremented and
+// decremented explicitly with calls to Retain() and Release(). E.g.:
+//
+// class Foo : public ReferenceCounted<Foo> {
+//  public:
+//   Foo() : ReferenceCounted() {}
+//   ...
+// };
+//
+// void DoStuffWithAFoo() {
+//   Foo* foo = new Foo();  // Reference count starts at 1, so no explicit
+//                          // call to Retain is needed after allocation.
+//   ...
+//   foo->Release();
+// }
+template <class Derived>
+class ReferenceCounted {
+ public:
+  ReferenceCounted() :
+    ref_count_(1) {
+  }
+
+  ~ReferenceCounted() {
+    ASSERT(ref_count_ == 0);
+  }
+
+  void Retain() {
+    uintptr_t old = AtomicOperations::FetchAndIncrement(&ref_count_);
+    ASSERT(old > 0);
+  }
+
+  void Release() {
+    uintptr_t old = AtomicOperations::FetchAndDecrement(&ref_count_);
+    ASSERT(old > 0);
+    if (old == 1) {
+      delete static_cast<Derived*>(this);
+    }
+  }
+
+ private:
+  uintptr_t ref_count_;
+
+  // These are used only in the ASSERT below in RefCntReleaseScope.
+  uintptr_t ref_count() const { return ref_count_; }
+  friend class RefCntReleaseScope<Derived>;
+  DISALLOW_COPY_AND_ASSIGN(ReferenceCounted);
+};
+
+// Creates a scope at the end of which a reference counted object is
+// Released. This is useful for reference counted objects recieved by the IO
+// Service, which have already been Retained E.g.:
+//
+// CObject* Foo::FooRequest(const CObjectArray& request) {
+//   Foo* foo = CObjectToFoo(request[0]);
+//   RefCntReleaseScope<Foo> rs(foo);
+//   ...
+// }
+template <class Target>
+class RefCntReleaseScope {
+ public:
+  explicit RefCntReleaseScope(ReferenceCounted<Target>* t) : target_(t) {
+    ASSERT(target_ != NULL);
+    ASSERT(target_->ref_count() > 0);
+  }
+  ~RefCntReleaseScope() {
+    target_->Release();
+  }
+
+ private:
+  ReferenceCounted<Target>* target_;
+
+  DISALLOW_ALLOCATION();
+  DISALLOW_COPY_AND_ASSIGN(RefCntReleaseScope);
+};
+
+// Instances of RetainedPointer manage Retaining and Releasing reference counted
+// objects. There are two ways to use it. First, it can be used as a field in
+// a class, e.g.:
+//
+// class Foo {
+//  private:
+//   RetainedPointer<Bar> bar_;
+//  public:
+//   explicit Foo(Bar* b) : bar_(b) {}
+// }
+//
+// In this case, b will be Retained in Foo's constructor, and Released
+// automatically during Foo's destructor.
+//
+// RetainedPointer can also be used as a scope, as with RefCntReleaseScope,
+// with the difference that entering the scope also Retains the pointer, e.g.:
+//
+// void RetainAndDoStuffWithFoo(Foo* foo) {
+//   RetainedPointer<Foo> retained(foo);
+//   ..
+// }
+//
+// This Retains foo on entry and Releases foo at every exit from the scope.
+//
+// The underlying pointer can be accessed with the get() and set() methods.
+// Overwriting a non-NULL pointer with set causes that pointer to be Released.
+template <class Target>
+class RetainedPointer {
+ public:
+  RetainedPointer() : target_(NULL) {}
+
+  explicit RetainedPointer(ReferenceCounted<Target>* t) : target_(t) {
+    if (target_ != NULL) {
+      target_->Retain();
+    }
+  }
+
+  ~RetainedPointer() {
+    if (target_ != NULL) {
+      target_->Release();
+    }
+  }
+
+  void set(ReferenceCounted<Target>* t) {
+    if (target_ != NULL) {
+      target_->Release();
+    }
+    target_ = t;
+    if (target_ != NULL) {
+      target_->Retain();
+    }
+  }
+
+  Target* get() const {
+    return static_cast<Target*>(target_);
+  }
+
+ private:
+  ReferenceCounted<Target>* target_;
+
+  DISALLOW_ALLOCATION();
+  DISALLOW_COPY_AND_ASSIGN(RetainedPointer);
+};
+
+}  // namespace bin
+}  // namespace dart
+
+#endif  // BIN_REFERENCE_COUNTING_H_