http://git-wip-us.apache.org/repos/asf/incubator-hawq/blob/bc0904ab/depends/libhdfs3/gtest/include/gtest/internal/gtest-linked_ptr.h
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+// Copyright 2003 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.
+//
+// Authors: Dan Egnor (eg...@google.com)
+//
+// A "smart" pointer type with reference tracking. Every pointer to a
+// particular object is kept on a circular linked list. When the last pointer
+// to an object is destroyed or reassigned, the object is deleted.
+//
+// Used properly, this deletes the object when the last reference goes away.
+// There are several caveats:
+// - Like all reference counting schemes, cycles lead to leaks.
+// - Each smart pointer is actually two pointers (8 bytes instead of 4).
+// - Every time a pointer is assigned, the entire list of pointers to that
+// object is traversed. This class is therefore NOT SUITABLE when there
+// will often be more than two or three pointers to a particular object.
+// - References are only tracked as long as linked_ptr<> objects are copied.
+// If a linked_ptr<> is converted to a raw pointer and back, BAD THINGS
+// will happen (double deletion).
+//
+// A good use of this class is storing object references in STL containers.
+// You can safely put linked_ptr<> in a vector<>.
+// Other uses may not be as good.
+//
+// Note: If you use an incomplete type with linked_ptr<>, the class
+// *containing* linked_ptr<> must have a constructor and destructor (even
+// if they do nothing!).
+//
+// Bill Gibbons suggested we use something like this.
+//
+// Thread Safety:
+// Unlike other linked_ptr implementations, in this implementation
+// a linked_ptr object is thread-safe in the sense that:
+// - it's safe to copy linked_ptr objects concurrently,
+// - it's safe to copy *from* a linked_ptr and read its underlying
+// raw pointer (e.g. via get()) concurrently, and
+// - it's safe to write to two linked_ptrs that point to the same
+// shared object concurrently.
+// TODO(w...@google.com): rename this to safe_linked_ptr to avoid
+// confusion with normal linked_ptr.
+
+#ifndef GTEST_INCLUDE_GTEST_INTERNAL_GTEST_LINKED_PTR_H_
+#define GTEST_INCLUDE_GTEST_INTERNAL_GTEST_LINKED_PTR_H_
+
+#include <stdlib.h>
+#include <assert.h>
+
+#include "gtest/internal/gtest-port.h"
+
+namespace testing {
+namespace internal {
+
+// Protects copying of all linked_ptr objects.
+GTEST_API_ GTEST_DECLARE_STATIC_MUTEX_(g_linked_ptr_mutex);
+
+// This is used internally by all instances of linked_ptr<>. It needs to be
+// a non-template class because different types of linked_ptr<> can refer to
+// the same object (linked_ptr<Superclass>(obj) vs linked_ptr<Subclass>(obj)).
+// So, it needs to be possible for different types of linked_ptr to participate
+// in the same circular linked list, so we need a single class type here.
+//
+// DO NOT USE THIS CLASS DIRECTLY YOURSELF. Use linked_ptr<T>.
+class linked_ptr_internal {
+ public:
+ // Create a new circle that includes only this instance.
+ void join_new() {
+ next_ = this;
+ }
+
+ // Many linked_ptr operations may change p.link_ for some linked_ptr
+ // variable p in the same circle as this object. Therefore we need
+ // to prevent two such operations from occurring concurrently.
+ //
+ // Note that different types of linked_ptr objects can coexist in a
+ // circle (e.g. linked_ptr<Base>, linked_ptr<Derived1>, and
+ // linked_ptr<Derived2>). Therefore we must use a single mutex to
+ // protect all linked_ptr objects. This can create serious
+ // contention in production code, but is acceptable in a testing
+ // framework.
+
+ // Join an existing circle.
+ void join(linked_ptr_internal const* ptr)
+ GTEST_LOCK_EXCLUDED_(g_linked_ptr_mutex) {
+ MutexLock lock(&g_linked_ptr_mutex);
+
+ linked_ptr_internal const* p = ptr;
+ while (p->next_ != ptr) p = p->next_;
+ p->next_ = this;
+ next_ = ptr;
+ }
+
+ // Leave whatever circle we're part of. Returns true if we were the
+ // last member of the circle. Once this is done, you can join() another.
+ bool depart()
+ GTEST_LOCK_EXCLUDED_(g_linked_ptr_mutex) {
+ MutexLock lock(&g_linked_ptr_mutex);
+
+ if (next_ == this) return true;
+ linked_ptr_internal const* p = next_;
+ while (p->next_ != this) p = p->next_;
+ p->next_ = next_;
+ return false;
+ }
+
+ private:
+ mutable linked_ptr_internal const* next_;
+};
+
+template <typename T>
+class linked_ptr {
+ public:
+ typedef T element_type;
+
+ // Take over ownership of a raw pointer. This should happen as soon as
+ // possible after the object is created.
+ explicit linked_ptr(T* ptr = NULL) { capture(ptr); }
+ ~linked_ptr() { depart(); }
+
+ // Copy an existing linked_ptr<>, adding ourselves to the list of references.
+ template <typename U> linked_ptr(linked_ptr<U> const& ptr) { copy(&ptr); }
+ linked_ptr(linked_ptr const& ptr) { // NOLINT
+ assert(&ptr != this);
+ copy(&ptr);
+ }
+
+ // Assignment releases the old value and acquires the new.
+ template <typename U> linked_ptr& operator=(linked_ptr<U> const& ptr) {
+ depart();
+ copy(&ptr);
+ return *this;
+ }
+
+ linked_ptr& operator=(linked_ptr const& ptr) {
+ if (&ptr != this) {
+ depart();
+ copy(&ptr);
+ }
+ return *this;
+ }
+
+ // Smart pointer members.
+ void reset(T* ptr = NULL) {
+ depart();
+ capture(ptr);
+ }
+ T* get() const { return value_; }
+ T* operator->() const { return value_; }
+ T& operator*() const { return *value_; }
+
+ bool operator==(T* p) const { return value_ == p; }
+ bool operator!=(T* p) const { return value_ != p; }
+ template <typename U>
+ bool operator==(linked_ptr<U> const& ptr) const {
+ return value_ == ptr.get();
+ }
+ template <typename U>
+ bool operator!=(linked_ptr<U> const& ptr) const {
+ return value_ != ptr.get();
+ }
+
+ private:
+ template <typename U>
+ friend class linked_ptr;
+
+ T* value_;
+ linked_ptr_internal link_;
+
+ void depart() {
+ if (link_.depart()) delete value_;
+ }
+
+ void capture(T* ptr) {
+ value_ = ptr;
+ link_.join_new();
+ }
+
+ template <typename U> void copy(linked_ptr<U> const* ptr) {
+ value_ = ptr->get();
+ if (value_)
+ link_.join(&ptr->link_);
+ else
+ link_.join_new();
+ }
+};
+
+template<typename T> inline
+bool operator==(T* ptr, const linked_ptr<T>& x) {
+ return ptr == x.get();
+}
+
+template<typename T> inline
+bool operator!=(T* ptr, const linked_ptr<T>& x) {
+ return ptr != x.get();
+}
+
+// A function to convert T* into linked_ptr<T>
+// Doing e.g. make_linked_ptr(new FooBarBaz<type>(arg)) is a shorter notation
+// for linked_ptr<FooBarBaz<type> >(new FooBarBaz<type>(arg))
+template <typename T>
+linked_ptr<T> make_linked_ptr(T* ptr) {
+ return linked_ptr<T>(ptr);
+}
+
+} // namespace internal
+} // namespace testing
+
+#endif // GTEST_INCLUDE_GTEST_INTERNAL_GTEST_LINKED_PTR_H_
