1 /* 2 * libjingle 3 * Copyright 2004--2010, Google Inc. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions are met: 7 * 8 * 1. Redistributions of source code must retain the above copyright notice, 9 * this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright notice, 11 * this list of conditions and the following disclaimer in the documentation 12 * and/or other materials provided with the distribution. 13 * 3. The name of the author may not be used to endorse or promote products 14 * derived from this software without specific prior written permission. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED 17 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 18 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO 19 * EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 20 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, 21 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; 22 * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, 23 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR 24 * OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF 25 * ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 26 */ 27 28 #ifndef TALK_BASE_REFERENCECOUNTEDSINGLETONFACTORY_H_ 29 #define TALK_BASE_REFERENCECOUNTEDSINGLETONFACTORY_H_ 30 31 #include "talk/base/common.h" 32 #include "talk/base/criticalsection.h" 33 #include "talk/base/logging.h" 34 #include "talk/base/scoped_ptr.h" 35 36 namespace talk_base { 37 38 template <typename Interface> class rcsf_ptr; 39 40 // A ReferenceCountedSingletonFactory is an object which owns another object, 41 // and doles out the owned object to consumers in a reference-counted manner. 42 // Thus, the factory owns at most one object of the desired kind, and 43 // hands consumers a special pointer to it, through which they can access it. 44 // When the consumers delete the pointer, the reference count goes down, 45 // and if the reference count hits zero, the factory can throw the object 46 // away. If a consumer requests the pointer and the factory has none, 47 // it can create one on the fly and pass it back. 48 template <typename Interface> 49 class ReferenceCountedSingletonFactory { 50 friend class rcsf_ptr<Interface>; 51 public: 52 ReferenceCountedSingletonFactory() : ref_count_(0) {} 53 54 virtual ~ReferenceCountedSingletonFactory() { 55 ASSERT(ref_count_ == 0); 56 } 57 58 protected: 59 // Must be implemented in a sub-class. The sub-class may choose whether or not 60 // to cache the instance across lifetimes by either reset()'ing or not 61 // reset()'ing the scoped_ptr in CleanupInstance(). 62 virtual bool SetupInstance() = 0; 63 virtual void CleanupInstance() = 0; 64 65 scoped_ptr<Interface> instance_; 66 67 private: 68 Interface* GetInstance() { 69 talk_base::CritScope cs(&crit_); 70 if (ref_count_ == 0) { 71 if (!SetupInstance()) { 72 LOG(LS_VERBOSE) << "Failed to setup instance"; 73 return NULL; 74 } 75 ASSERT(instance_.get() != NULL); 76 } 77 ++ref_count_; 78 79 LOG(LS_VERBOSE) << "Number of references: " << ref_count_; 80 return instance_.get(); 81 } 82 83 void ReleaseInstance() { 84 talk_base::CritScope cs(&crit_); 85 ASSERT(ref_count_ > 0); 86 ASSERT(instance_.get() != NULL); 87 --ref_count_; 88 LOG(LS_VERBOSE) << "Number of references: " << ref_count_; 89 if (ref_count_ == 0) { 90 CleanupInstance(); 91 } 92 } 93 94 CriticalSection crit_; 95 int ref_count_; 96 97 DISALLOW_COPY_AND_ASSIGN(ReferenceCountedSingletonFactory); 98 }; 99 100 template <typename Interface> 101 class rcsf_ptr { 102 public: 103 // Create a pointer that uses the factory to get the instance. 104 // This is lazy - it won't generate the instance until it is requested. 105 explicit rcsf_ptr(ReferenceCountedSingletonFactory<Interface>* factory) 106 : instance_(NULL), 107 factory_(factory) { 108 } 109 110 ~rcsf_ptr() { 111 release(); 112 } 113 114 Interface& operator*() { 115 EnsureAcquired(); 116 return *instance_; 117 } 118 119 Interface* operator->() { 120 EnsureAcquired(); 121 return instance_; 122 } 123 124 // Gets the pointer, creating the singleton if necessary. May return NULL if 125 // creation failed. 126 Interface* get() { 127 Acquire(); 128 return instance_; 129 } 130 131 // Set instance to NULL and tell the factory we aren't using the instance 132 // anymore. 133 void release() { 134 if (instance_) { 135 instance_ = NULL; 136 factory_->ReleaseInstance(); 137 } 138 } 139 140 // Lets us know whether instance is valid or not right now. 141 // Even though attempts to use the instance will automatically create it, it 142 // is advisable to check this because creation can fail. 143 bool valid() const { 144 return instance_ != NULL; 145 } 146 147 // Returns the factory that this pointer is using. 148 ReferenceCountedSingletonFactory<Interface>* factory() const { 149 return factory_; 150 } 151 152 private: 153 void EnsureAcquired() { 154 Acquire(); 155 ASSERT(instance_ != NULL); 156 } 157 158 void Acquire() { 159 // Since we're getting a singleton back, acquire is a noop if instance is 160 // already populated. 161 if (!instance_) { 162 instance_ = factory_->GetInstance(); 163 } 164 } 165 166 Interface* instance_; 167 ReferenceCountedSingletonFactory<Interface>* factory_; 168 169 DISALLOW_IMPLICIT_CONSTRUCTORS(rcsf_ptr); 170 }; 171 172 }; // namespace talk_base 173 174 #endif // TALK_BASE_REFERENCECOUNTEDSINGLETONFACTORY_H_ 175