Source release v3.5.0

core/include/shared_ptr.h

@@ -0,0 +1,222 @@
+// Copyright 2017 Google 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:
+//
+//     * Redistributions of source code must retain the above copyright
+// notice, this list of conditions and the following disclaimer.
+//     * 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.
+//     * Neither the name of Google Inc. nor the names of its
+// contributors may be used to endorse or promote products derived from
+// this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND 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 THE COPYRIGHT
+// OWNER OR 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.
+
+// from google3/util/gtl/shared_ptr.h
+// from protobuf/src/google/protobuf/stubs/shared_ptr.h
+
+#ifndef WVCDM_CORE_SHARED_PTR_H__
+#define WVCDM_CORE_SHARED_PTR_H__
+
+#include <algorithm>  // for swap
+#include <stddef.h>
+#include <memory>
+
+#include "wv_cdm_types.h"
+
+namespace {
+bool Barrier_AtomicIncrement(volatile uint32_t* ptr, uint32_t value) {
+  *ptr += value;
+  return *ptr;
+}
+bool NoBarrier_AtomicIncrement(volatile uint32_t* ptr, uint32_t value) {
+  *ptr += value;
+  return *ptr;
+}
+
+inline bool RefCountDec(volatile uint32_t *ptr) {
+  return Barrier_AtomicIncrement(ptr, -1) != 0;
+}
+
+inline void RefCountInc(volatile uint32_t *ptr) {
+  NoBarrier_AtomicIncrement(ptr, 1);
+}
+
+}  // namespace
+
+namespace wvcdm {
+
+template <typename T> class shared_ptr;
+
+// This class is an internal implementation detail for shared_ptr. If two
+// shared_ptrs point to the same object, they also share a control block.
+// An "empty" shared_pointer refers to NULL and also has a NULL control block.
+// It contains all of the state that's needed for reference counting or any
+// other kind of resource management. In this implementation the control block
+// consists of a single reference count (the number of shared_ptrs that
+// share ownership of the object).
+class SharedPtrControlBlock {
+  template <typename T> friend class shared_ptr;
+ private:
+  SharedPtrControlBlock() : refcount_(1) {}
+  uint32_t refcount_;
+};
+
+// Forward declaration. The class is defined below.
+template <typename T> class enable_shared_from_this;
+
+template <typename T>
+class shared_ptr {
+ public:
+  typedef T element_type;
+
+  shared_ptr() : ptr_(NULL), control_block_(NULL) {}
+
+  explicit shared_ptr(T* ptr)
+      : ptr_(ptr),
+        control_block_(ptr != NULL ? new SharedPtrControlBlock : NULL) {
+  }
+
+  // Copy constructor: makes this object a copy of ptr, and increments
+  // the reference count.
+  template <typename U>
+  shared_ptr(const shared_ptr<U>& ptr)
+      : ptr_(NULL),
+        control_block_(NULL) {
+    Initialize(ptr);
+  }
+  // Need non-templated version to prevent the compiler-generated default
+  shared_ptr(const shared_ptr<T>& ptr)
+      : ptr_(NULL),
+        control_block_(NULL) {
+    Initialize(ptr);
+  }
+
+  // Assignment operator. Replaces the existing shared_ptr with ptr.
+  // Increment ptr's reference count and decrement the one being replaced.
+  template <typename U>
+  shared_ptr<T>& operator=(const shared_ptr<U>& ptr) {
+    if (ptr_ != ptr.ptr_) {
+      shared_ptr<T> me(ptr);   // will hold our previous state to be destroyed.
+      swap(me);
+    }
+    return *this;
+  }
+
+  // Need non-templated version to prevent the compiler-generated default
+  shared_ptr<T>& operator=(const shared_ptr<T>& ptr) {
+    if (ptr_ != ptr.ptr_) {
+      shared_ptr<T> me(ptr);   // will hold our previous state to be destroyed.
+      swap(me);
+    }
+    return *this;
+  }
+
+  ~shared_ptr() {
+    if (ptr_ != NULL) {
+      if (!RefCountDec(&control_block_->refcount_)) {
+        delete ptr_;
+      }
+    }
+  }
+
+  // Replaces underlying raw pointer with the one passed in.  The reference
+  // count is set to one (or zero if the pointer is NULL) for the pointer
+  // being passed in and decremented for the one being replaced.
+  //
+  // If you have a compilation error with this code, make sure you aren't
+  // passing NULL, nullptr, or 0 to this function.  Call reset without an
+  // argument to reset to a null ptr.
+  template <typename Y>
+  void reset(Y* p) {
+    if (p != ptr_) {
+      shared_ptr<T> tmp(p);
+      tmp.swap(*this);
+    }
+  }
+
+  void reset() {
+    reset(static_cast<T*>(NULL));
+  }
+
+  // Exchanges the contents of this with the contents of r.  This function
+  // supports more efficient swapping since it eliminates the need for a
+  // temporary shared_ptr object.
+  void swap(shared_ptr<T>& r) {
+    using std::swap;  // http://go/using-std-swap
+    swap(ptr_, r.ptr_);
+    swap(control_block_, r.control_block_);
+  }
+
+  // The following function is useful for gaining access to the underlying
+  // pointer when a shared_ptr remains in scope so the reference-count is
+  // known to be > 0 (e.g. for parameter passing).
+  T* get() const {
+    return ptr_;
+  }
+
+  T& operator*() const {
+    return *ptr_;
+  }
+
+  T* operator->() const {
+    return ptr_;
+  }
+
+  long use_count() const {
+    return control_block_ ? control_block_->refcount_ : 1;
+  }
+
+  bool unique() const {
+    return use_count() == 1;
+  }
+
+ private:
+  // If r is non-empty, initialize *this to share ownership with r,
+  // increasing the underlying reference count.
+  // If r is empty, *this remains empty.
+  // Requires: this is empty, namely this->ptr_ == NULL.
+  template <typename U>
+  void Initialize(const shared_ptr<U>& r) {
+    // This performs a static_cast on r.ptr_ to U*, which is a no-op since it
+    // is already a U*. So initialization here requires that r.ptr_ is
+    // implicitly convertible to T*.
+    InitializeWithStaticCast<U>(r);
+  }
+
+  // Initializes *this as described in Initialize, but additionally performs a
+  // static_cast from r.ptr_ (V*) to U*.
+  // NOTE(gfc): We'd need a more general form to support const_pointer_cast and
+  // dynamic_pointer_cast, but those operations are sufficiently discouraged
+  // that supporting static_pointer_cast is sufficient.
+  template <typename U, typename V>
+  void InitializeWithStaticCast(const shared_ptr<V>& r) {
+    if (r.control_block_ != NULL) {
+      RefCountInc(&r.control_block_->refcount_);
+
+      ptr_ = static_cast<U*>(r.ptr_);
+      control_block_ = r.control_block_;
+    }
+  }
+
+  T* ptr_;
+  SharedPtrControlBlock* control_block_;
+};
+
+}  // namespace wvcdm
+
+#endif  // WVCDM_CORE_SHARED_PTR_H__