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Diffstat (limited to 'security/sandbox/chromium/base/memory/singleton.h')
| -rw-r--r-- | security/sandbox/chromium/base/memory/singleton.h | 284 |
1 files changed, 0 insertions, 284 deletions
diff --git a/security/sandbox/chromium/base/memory/singleton.h b/security/sandbox/chromium/base/memory/singleton.h deleted file mode 100644 index 79e4441a8..000000000 --- a/security/sandbox/chromium/base/memory/singleton.h +++ /dev/null @@ -1,284 +0,0 @@ -// Copyright (c) 2011 The Chromium Authors. All rights reserved. -// Use of this source code is governed by a BSD-style license that can be -// found in the LICENSE file. - -// PLEASE READ: Do you really need a singleton? -// -// Singletons make it hard to determine the lifetime of an object, which can -// lead to buggy code and spurious crashes. -// -// Instead of adding another singleton into the mix, try to identify either: -// a) An existing singleton that can manage your object's lifetime -// b) Locations where you can deterministically create the object and pass -// into other objects -// -// If you absolutely need a singleton, please keep them as trivial as possible -// and ideally a leaf dependency. Singletons get problematic when they attempt -// to do too much in their destructor or have circular dependencies. - -#ifndef BASE_MEMORY_SINGLETON_H_ -#define BASE_MEMORY_SINGLETON_H_ - -#include "base/at_exit.h" -#include "base/atomicops.h" -#include "base/base_export.h" -#include "base/macros.h" -#include "base/memory/aligned_memory.h" -#include "base/threading/thread_restrictions.h" - -namespace base { -namespace internal { - -// Our AtomicWord doubles as a spinlock, where a value of -// kBeingCreatedMarker means the spinlock is being held for creation. -static const subtle::AtomicWord kBeingCreatedMarker = 1; - -// We pull out some of the functionality into a non-templated function, so that -// we can implement the more complicated pieces out of line in the .cc file. -BASE_EXPORT subtle::AtomicWord WaitForInstance(subtle::AtomicWord* instance); - -class DeleteTraceLogForTesting; - -} // namespace internal - - -// Default traits for Singleton<Type>. Calls operator new and operator delete on -// the object. Registers automatic deletion at process exit. -// Overload if you need arguments or another memory allocation function. -template<typename Type> -struct DefaultSingletonTraits { - // Allocates the object. - static Type* New() { - // The parenthesis is very important here; it forces POD type - // initialization. - return new Type(); - } - - // Destroys the object. - static void Delete(Type* x) { - delete x; - } - - // Set to true to automatically register deletion of the object on process - // exit. See below for the required call that makes this happen. - static const bool kRegisterAtExit = true; - -#ifndef NDEBUG - // Set to false to disallow access on a non-joinable thread. This is - // different from kRegisterAtExit because StaticMemorySingletonTraits allows - // access on non-joinable threads, and gracefully handles this. - static const bool kAllowedToAccessOnNonjoinableThread = false; -#endif -}; - - -// Alternate traits for use with the Singleton<Type>. Identical to -// DefaultSingletonTraits except that the Singleton will not be cleaned up -// at exit. -template<typename Type> -struct LeakySingletonTraits : public DefaultSingletonTraits<Type> { - static const bool kRegisterAtExit = false; -#ifndef NDEBUG - static const bool kAllowedToAccessOnNonjoinableThread = true; -#endif -}; - - -// Alternate traits for use with the Singleton<Type>. Allocates memory -// for the singleton instance from a static buffer. The singleton will -// be cleaned up at exit, but can't be revived after destruction unless -// the Resurrect() method is called. -// -// This is useful for a certain category of things, notably logging and -// tracing, where the singleton instance is of a type carefully constructed to -// be safe to access post-destruction. -// In logging and tracing you'll typically get stray calls at odd times, like -// during static destruction, thread teardown and the like, and there's a -// termination race on the heap-based singleton - e.g. if one thread calls -// get(), but then another thread initiates AtExit processing, the first thread -// may call into an object residing in unallocated memory. If the instance is -// allocated from the data segment, then this is survivable. -// -// The destructor is to deallocate system resources, in this case to unregister -// a callback the system will invoke when logging levels change. Note that -// this is also used in e.g. Chrome Frame, where you have to allow for the -// possibility of loading briefly into someone else's process space, and -// so leaking is not an option, as that would sabotage the state of your host -// process once you've unloaded. -template <typename Type> -struct StaticMemorySingletonTraits { - // WARNING: User has to deal with get() in the singleton class - // this is traits for returning NULL. - static Type* New() { - // Only constructs once and returns pointer; otherwise returns NULL. - if (subtle::NoBarrier_AtomicExchange(&dead_, 1)) - return NULL; - - return new(buffer_.void_data()) Type(); - } - - static void Delete(Type* p) { - if (p != NULL) - p->Type::~Type(); - } - - static const bool kRegisterAtExit = true; - static const bool kAllowedToAccessOnNonjoinableThread = true; - - // Exposed for unittesting. - static void Resurrect() { subtle::NoBarrier_Store(&dead_, 0); } - - private: - static AlignedMemory<sizeof(Type), ALIGNOF(Type)> buffer_; - // Signal the object was already deleted, so it is not revived. - static subtle::Atomic32 dead_; -}; - -template <typename Type> -AlignedMemory<sizeof(Type), ALIGNOF(Type)> - StaticMemorySingletonTraits<Type>::buffer_; -template <typename Type> -subtle::Atomic32 StaticMemorySingletonTraits<Type>::dead_ = 0; - -// The Singleton<Type, Traits, DifferentiatingType> class manages a single -// instance of Type which will be created on first use and will be destroyed at -// normal process exit). The Trait::Delete function will not be called on -// abnormal process exit. -// -// DifferentiatingType is used as a key to differentiate two different -// singletons having the same memory allocation functions but serving a -// different purpose. This is mainly used for Locks serving different purposes. -// -// Example usage: -// -// In your header: -// template <typename T> struct DefaultSingletonTraits; -// class FooClass { -// public: -// static FooClass* GetInstance(); <-- See comment below on this. -// void Bar() { ... } -// private: -// FooClass() { ... } -// friend struct DefaultSingletonTraits<FooClass>; -// -// DISALLOW_COPY_AND_ASSIGN(FooClass); -// }; -// -// In your source file: -// #include "base/memory/singleton.h" -// FooClass* FooClass::GetInstance() { -// return Singleton<FooClass>::get(); -// } -// -// And to call methods on FooClass: -// FooClass::GetInstance()->Bar(); -// -// NOTE: The method accessing Singleton<T>::get() has to be named as GetInstance -// and it is important that FooClass::GetInstance() is not inlined in the -// header. This makes sure that when source files from multiple targets include -// this header they don't end up with different copies of the inlined code -// creating multiple copies of the singleton. -// -// Singleton<> has no non-static members and doesn't need to actually be -// instantiated. -// -// This class is itself thread-safe. The underlying Type must of course be -// thread-safe if you want to use it concurrently. Two parameters may be tuned -// depending on the user's requirements. -// -// Glossary: -// RAE = kRegisterAtExit -// -// On every platform, if Traits::RAE is true, the singleton will be destroyed at -// process exit. More precisely it uses AtExitManager which requires an -// object of this type to be instantiated. AtExitManager mimics the semantics -// of atexit() such as LIFO order but under Windows is safer to call. For more -// information see at_exit.h. -// -// If Traits::RAE is false, the singleton will not be freed at process exit, -// thus the singleton will be leaked if it is ever accessed. Traits::RAE -// shouldn't be false unless absolutely necessary. Remember that the heap where -// the object is allocated may be destroyed by the CRT anyway. -// -// Caveats: -// (a) Every call to get(), operator->() and operator*() incurs some overhead -// (16ns on my P4/2.8GHz) to check whether the object has already been -// initialized. You may wish to cache the result of get(); it will not -// change. -// -// (b) Your factory function must never throw an exception. This class is not -// exception-safe. -// - -template <typename Type, - typename Traits = DefaultSingletonTraits<Type>, - typename DifferentiatingType = Type> -class Singleton { - private: - // Classes using the Singleton<T> pattern should declare a GetInstance() - // method and call Singleton::get() from within that. - friend Type* Type::GetInstance(); - - // Allow TraceLog tests to test tracing after OnExit. - friend class internal::DeleteTraceLogForTesting; - - // This class is safe to be constructed and copy-constructed since it has no - // member. - - // Return a pointer to the one true instance of the class. - static Type* get() { -#ifndef NDEBUG - // Avoid making TLS lookup on release builds. - if (!Traits::kAllowedToAccessOnNonjoinableThread) - ThreadRestrictions::AssertSingletonAllowed(); -#endif - - // The load has acquire memory ordering as the thread which reads the - // instance_ pointer must acquire visibility over the singleton data. - subtle::AtomicWord value = subtle::Acquire_Load(&instance_); - if (value != 0 && value != internal::kBeingCreatedMarker) { - return reinterpret_cast<Type*>(value); - } - - // Object isn't created yet, maybe we will get to create it, let's try... - if (subtle::Acquire_CompareAndSwap(&instance_, 0, - internal::kBeingCreatedMarker) == 0) { - // instance_ was NULL and is now kBeingCreatedMarker. Only one thread - // will ever get here. Threads might be spinning on us, and they will - // stop right after we do this store. - Type* newval = Traits::New(); - - // Releases the visibility over instance_ to the readers. - subtle::Release_Store(&instance_, - reinterpret_cast<subtle::AtomicWord>(newval)); - - if (newval != NULL && Traits::kRegisterAtExit) - AtExitManager::RegisterCallback(OnExit, NULL); - - return newval; - } - - // We hit a race. Wait for the other thread to complete it. - value = internal::WaitForInstance(&instance_); - - return reinterpret_cast<Type*>(value); - } - - // Adapter function for use with AtExit(). This should be called single - // threaded, so don't use atomic operations. - // Calling OnExit while singleton is in use by other threads is a mistake. - static void OnExit(void* /*unused*/) { - // AtExit should only ever be register after the singleton instance was - // created. We should only ever get here with a valid instance_ pointer. - Traits::Delete(reinterpret_cast<Type*>(subtle::NoBarrier_Load(&instance_))); - instance_ = 0; - } - static subtle::AtomicWord instance_; -}; - -template <typename Type, typename Traits, typename DifferentiatingType> -subtle::AtomicWord Singleton<Type, Traits, DifferentiatingType>::instance_ = 0; - -} // namespace base - -#endif // BASE_MEMORY_SINGLETON_H_ |