Qucs-core  0.0.19
gtest-linked_ptr.h
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00001 // Copyright 2003 Google Inc.
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00003 //
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00010 //     * Redistributions in binary form must reproduce the above
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00018 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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00029 //
00030 // Authors: Dan Egnor (egnor@google.com)
00031 //
00032 // A "smart" pointer type with reference tracking.  Every pointer to a
00033 // particular object is kept on a circular linked list.  When the last pointer
00034 // to an object is destroyed or reassigned, the object is deleted.
00035 //
00036 // Used properly, this deletes the object when the last reference goes away.
00037 // There are several caveats:
00038 // - Like all reference counting schemes, cycles lead to leaks.
00039 // - Each smart pointer is actually two pointers (8 bytes instead of 4).
00040 // - Every time a pointer is assigned, the entire list of pointers to that
00041 //   object is traversed.  This class is therefore NOT SUITABLE when there
00042 //   will often be more than two or three pointers to a particular object.
00043 // - References are only tracked as long as linked_ptr<> objects are copied.
00044 //   If a linked_ptr<> is converted to a raw pointer and back, BAD THINGS
00045 //   will happen (double deletion).
00046 //
00047 // A good use of this class is storing object references in STL containers.
00048 // You can safely put linked_ptr<> in a vector<>.
00049 // Other uses may not be as good.
00050 //
00051 // Note: If you use an incomplete type with linked_ptr<>, the class
00052 // *containing* linked_ptr<> must have a constructor and destructor (even
00053 // if they do nothing!).
00054 //
00055 // Bill Gibbons suggested we use something like this.
00056 //
00057 // Thread Safety:
00058 //   Unlike other linked_ptr implementations, in this implementation
00059 //   a linked_ptr object is thread-safe in the sense that:
00060 //     - it's safe to copy linked_ptr objects concurrently,
00061 //     - it's safe to copy *from* a linked_ptr and read its underlying
00062 //       raw pointer (e.g. via get()) concurrently, and
00063 //     - it's safe to write to two linked_ptrs that point to the same
00064 //       shared object concurrently.
00065 // TODO(wan@google.com): rename this to safe_linked_ptr to avoid
00066 // confusion with normal linked_ptr.
00067 
00068 #ifndef GTEST_INCLUDE_GTEST_INTERNAL_GTEST_LINKED_PTR_H_
00069 #define GTEST_INCLUDE_GTEST_INTERNAL_GTEST_LINKED_PTR_H_
00070 
00071 #include <stdlib.h>
00072 #include <assert.h>
00073 
00074 #include "gtest/internal/gtest-port.h"
00075 
00076 namespace testing {
00077 namespace internal {
00078 
00079 // Protects copying of all linked_ptr objects.
00080 GTEST_API_ GTEST_DECLARE_STATIC_MUTEX_(g_linked_ptr_mutex);
00081 
00082 // This is used internally by all instances of linked_ptr<>.  It needs to be
00083 // a non-template class because different types of linked_ptr<> can refer to
00084 // the same object (linked_ptr<Superclass>(obj) vs linked_ptr<Subclass>(obj)).
00085 // So, it needs to be possible for different types of linked_ptr to participate
00086 // in the same circular linked list, so we need a single class type here.
00087 //
00088 // DO NOT USE THIS CLASS DIRECTLY YOURSELF.  Use linked_ptr<T>.
00089 class linked_ptr_internal {
00090  public:
00091   // Create a new circle that includes only this instance.
00092   void join_new() {
00093     next_ = this;
00094   }
00095 
00096   // Many linked_ptr operations may change p.link_ for some linked_ptr
00097   // variable p in the same circle as this object.  Therefore we need
00098   // to prevent two such operations from occurring concurrently.
00099   //
00100   // Note that different types of linked_ptr objects can coexist in a
00101   // circle (e.g. linked_ptr<Base>, linked_ptr<Derived1>, and
00102   // linked_ptr<Derived2>).  Therefore we must use a single mutex to
00103   // protect all linked_ptr objects.  This can create serious
00104   // contention in production code, but is acceptable in a testing
00105   // framework.
00106 
00107   // Join an existing circle.
00108   void join(linked_ptr_internal const* ptr)
00109       GTEST_LOCK_EXCLUDED_(g_linked_ptr_mutex) {
00110     MutexLock lock(&g_linked_ptr_mutex);
00111 
00112     linked_ptr_internal const* p = ptr;
00113     while (p->next_ != ptr) p = p->next_;
00114     p->next_ = this;
00115     next_ = ptr;
00116   }
00117 
00118   // Leave whatever circle we're part of.  Returns true if we were the
00119   // last member of the circle.  Once this is done, you can join() another.
00120   bool depart()
00121       GTEST_LOCK_EXCLUDED_(g_linked_ptr_mutex) {
00122     MutexLock lock(&g_linked_ptr_mutex);
00123 
00124     if (next_ == this) return true;
00125     linked_ptr_internal const* p = next_;
00126     while (p->next_ != this) p = p->next_;
00127     p->next_ = next_;
00128     return false;
00129   }
00130 
00131  private:
00132   mutable linked_ptr_internal const* next_;
00133 };
00134 
00135 template <typename T>
00136 class linked_ptr {
00137  public:
00138   typedef T element_type;
00139 
00140   // Take over ownership of a raw pointer.  This should happen as soon as
00141   // possible after the object is created.
00142   explicit linked_ptr(T* ptr = NULL) { capture(ptr); }
00143   ~linked_ptr() { depart(); }
00144 
00145   // Copy an existing linked_ptr<>, adding ourselves to the list of references.
00146   template <typename U> linked_ptr(linked_ptr<U> const& ptr) { copy(&ptr); }
00147   linked_ptr(linked_ptr const& ptr) {  // NOLINT
00148     assert(&ptr != this);
00149     copy(&ptr);
00150   }
00151 
00152   // Assignment releases the old value and acquires the new.
00153   template <typename U> linked_ptr& operator=(linked_ptr<U> const& ptr) {
00154     depart();
00155     copy(&ptr);
00156     return *this;
00157   }
00158 
00159   linked_ptr& operator=(linked_ptr const& ptr) {
00160     if (&ptr != this) {
00161       depart();
00162       copy(&ptr);
00163     }
00164     return *this;
00165   }
00166 
00167   // Smart pointer members.
00168   void reset(T* ptr = NULL) {
00169     depart();
00170     capture(ptr);
00171   }
00172   T* get() const { return value_; }
00173   T* operator->() const { return value_; }
00174   T& operator*() const { return *value_; }
00175 
00176   bool operator==(T* p) const { return value_ == p; }
00177   bool operator!=(T* p) const { return value_ != p; }
00178   template <typename U>
00179   bool operator==(linked_ptr<U> const& ptr) const {
00180     return value_ == ptr.get();
00181   }
00182   template <typename U>
00183   bool operator!=(linked_ptr<U> const& ptr) const {
00184     return value_ != ptr.get();
00185   }
00186 
00187  private:
00188   template <typename U>
00189   friend class linked_ptr;
00190 
00191   T* value_;
00192   linked_ptr_internal link_;
00193 
00194   void depart() {
00195     if (link_.depart()) delete value_;
00196   }
00197 
00198   void capture(T* ptr) {
00199     value_ = ptr;
00200     link_.join_new();
00201   }
00202 
00203   template <typename U> void copy(linked_ptr<U> const* ptr) {
00204     value_ = ptr->get();
00205     if (value_)
00206       link_.join(&ptr->link_);
00207     else
00208       link_.join_new();
00209   }
00210 };
00211 
00212 template<typename T> inline
00213 bool operator==(T* ptr, const linked_ptr<T>& x) {
00214   return ptr == x.get();
00215 }
00216 
00217 template<typename T> inline
00218 bool operator!=(T* ptr, const linked_ptr<T>& x) {
00219   return ptr != x.get();
00220 }
00221 
00222 // A function to convert T* into linked_ptr<T>
00223 // Doing e.g. make_linked_ptr(new FooBarBaz<type>(arg)) is a shorter notation
00224 // for linked_ptr<FooBarBaz<type> >(new FooBarBaz<type>(arg))
00225 template <typename T>
00226 linked_ptr<T> make_linked_ptr(T* ptr) {
00227   return linked_ptr<T>(ptr);
00228 }
00229 
00230 }  // namespace internal
00231 }  // namespace testing
00232 
00233 #endif  // GTEST_INCLUDE_GTEST_INTERNAL_GTEST_LINKED_PTR_H_