henrike@webrtc.org | f7795df | 2014-05-13 18:00:26 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 2004 The WebRTC Project Authors. All rights reserved. |
| 3 | * |
| 4 | * Use of this source code is governed by a BSD-style license |
| 5 | * that can be found in the LICENSE file in the root of the source |
| 6 | * tree. An additional intellectual property rights grant can be found |
| 7 | * in the file PATENTS. All contributing project authors may |
| 8 | * be found in the AUTHORS file in the root of the source tree. |
| 9 | */ |
| 10 | |
| 11 | #ifndef WEBRTC_BASE_REFERENCECOUNTEDSINGLETONFACTORY_H_ |
| 12 | #define WEBRTC_BASE_REFERENCECOUNTEDSINGLETONFACTORY_H_ |
| 13 | |
| 14 | #include "webrtc/base/common.h" |
| 15 | #include "webrtc/base/criticalsection.h" |
| 16 | #include "webrtc/base/logging.h" |
| 17 | #include "webrtc/base/scoped_ptr.h" |
| 18 | |
| 19 | namespace rtc { |
| 20 | |
| 21 | template <typename Interface> class rcsf_ptr; |
| 22 | |
| 23 | // A ReferenceCountedSingletonFactory is an object which owns another object, |
| 24 | // and doles out the owned object to consumers in a reference-counted manner. |
| 25 | // Thus, the factory owns at most one object of the desired kind, and |
| 26 | // hands consumers a special pointer to it, through which they can access it. |
| 27 | // When the consumers delete the pointer, the reference count goes down, |
| 28 | // and if the reference count hits zero, the factory can throw the object |
| 29 | // away. If a consumer requests the pointer and the factory has none, |
| 30 | // it can create one on the fly and pass it back. |
| 31 | template <typename Interface> |
| 32 | class ReferenceCountedSingletonFactory { |
| 33 | friend class rcsf_ptr<Interface>; |
| 34 | public: |
| 35 | ReferenceCountedSingletonFactory() : ref_count_(0) {} |
| 36 | |
| 37 | virtual ~ReferenceCountedSingletonFactory() { |
| 38 | ASSERT(ref_count_ == 0); |
| 39 | } |
| 40 | |
| 41 | protected: |
| 42 | // Must be implemented in a sub-class. The sub-class may choose whether or not |
| 43 | // to cache the instance across lifetimes by either reset()'ing or not |
| 44 | // reset()'ing the scoped_ptr in CleanupInstance(). |
| 45 | virtual bool SetupInstance() = 0; |
| 46 | virtual void CleanupInstance() = 0; |
| 47 | |
| 48 | scoped_ptr<Interface> instance_; |
| 49 | |
| 50 | private: |
| 51 | Interface* GetInstance() { |
| 52 | rtc::CritScope cs(&crit_); |
| 53 | if (ref_count_ == 0) { |
| 54 | if (!SetupInstance()) { |
| 55 | LOG(LS_VERBOSE) << "Failed to setup instance"; |
| 56 | return NULL; |
| 57 | } |
| 58 | ASSERT(instance_.get() != NULL); |
| 59 | } |
| 60 | ++ref_count_; |
| 61 | |
| 62 | LOG(LS_VERBOSE) << "Number of references: " << ref_count_; |
| 63 | return instance_.get(); |
| 64 | } |
| 65 | |
| 66 | void ReleaseInstance() { |
| 67 | rtc::CritScope cs(&crit_); |
| 68 | ASSERT(ref_count_ > 0); |
| 69 | ASSERT(instance_.get() != NULL); |
| 70 | --ref_count_; |
| 71 | LOG(LS_VERBOSE) << "Number of references: " << ref_count_; |
| 72 | if (ref_count_ == 0) { |
| 73 | CleanupInstance(); |
| 74 | } |
| 75 | } |
| 76 | |
| 77 | CriticalSection crit_; |
| 78 | int ref_count_; |
| 79 | |
| 80 | DISALLOW_COPY_AND_ASSIGN(ReferenceCountedSingletonFactory); |
| 81 | }; |
| 82 | |
| 83 | template <typename Interface> |
| 84 | class rcsf_ptr { |
| 85 | public: |
| 86 | // Create a pointer that uses the factory to get the instance. |
| 87 | // This is lazy - it won't generate the instance until it is requested. |
| 88 | explicit rcsf_ptr(ReferenceCountedSingletonFactory<Interface>* factory) |
| 89 | : instance_(NULL), |
| 90 | factory_(factory) { |
| 91 | } |
| 92 | |
| 93 | ~rcsf_ptr() { |
| 94 | release(); |
| 95 | } |
| 96 | |
| 97 | Interface& operator*() { |
| 98 | EnsureAcquired(); |
| 99 | return *instance_; |
| 100 | } |
| 101 | |
| 102 | Interface* operator->() { |
| 103 | EnsureAcquired(); |
| 104 | return instance_; |
| 105 | } |
| 106 | |
| 107 | // Gets the pointer, creating the singleton if necessary. May return NULL if |
| 108 | // creation failed. |
| 109 | Interface* get() { |
| 110 | Acquire(); |
| 111 | return instance_; |
| 112 | } |
| 113 | |
| 114 | // Set instance to NULL and tell the factory we aren't using the instance |
| 115 | // anymore. |
| 116 | void release() { |
| 117 | if (instance_) { |
| 118 | instance_ = NULL; |
| 119 | factory_->ReleaseInstance(); |
| 120 | } |
| 121 | } |
| 122 | |
| 123 | // Lets us know whether instance is valid or not right now. |
| 124 | // Even though attempts to use the instance will automatically create it, it |
| 125 | // is advisable to check this because creation can fail. |
| 126 | bool valid() const { |
| 127 | return instance_ != NULL; |
| 128 | } |
| 129 | |
| 130 | // Returns the factory that this pointer is using. |
| 131 | ReferenceCountedSingletonFactory<Interface>* factory() const { |
| 132 | return factory_; |
| 133 | } |
| 134 | |
| 135 | private: |
| 136 | void EnsureAcquired() { |
| 137 | Acquire(); |
| 138 | ASSERT(instance_ != NULL); |
| 139 | } |
| 140 | |
| 141 | void Acquire() { |
| 142 | // Since we're getting a singleton back, acquire is a noop if instance is |
| 143 | // already populated. |
| 144 | if (!instance_) { |
| 145 | instance_ = factory_->GetInstance(); |
| 146 | } |
| 147 | } |
| 148 | |
| 149 | Interface* instance_; |
| 150 | ReferenceCountedSingletonFactory<Interface>* factory_; |
| 151 | |
| 152 | DISALLOW_IMPLICIT_CONSTRUCTORS(rcsf_ptr); |
| 153 | }; |
| 154 | |
| 155 | }; // namespace rtc |
| 156 | |
| 157 | #endif // WEBRTC_BASE_REFERENCECOUNTEDSINGLETONFACTORY_H_ |