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Diffstat (limited to 'cpp/src/qpid/sys/LockPtr.h')
-rw-r--r-- | cpp/src/qpid/sys/LockPtr.h | 89 |
1 files changed, 0 insertions, 89 deletions
diff --git a/cpp/src/qpid/sys/LockPtr.h b/cpp/src/qpid/sys/LockPtr.h deleted file mode 100644 index 738a864317..0000000000 --- a/cpp/src/qpid/sys/LockPtr.h +++ /dev/null @@ -1,89 +0,0 @@ -#ifndef QPID_SYS_LOCKPTR_H -#define QPID_SYS_LOCKPTR_H - -/* - * - * Licensed to the Apache Software Foundation (ASF) under one - * or more contributor license agreements. See the NOTICE file - * distributed with this work for additional information - * regarding copyright ownership. The ASF licenses this file - * to you under the Apache License, Version 2.0 (the - * "License"); you may not use this file except in compliance - * with the License. You may obtain a copy of the License at - * - * http://www.apache.org/licenses/LICENSE-2.0 - * - * Unless required by applicable law or agreed to in writing, - * software distributed under the License is distributed on an - * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY - * KIND, either express or implied. See the License for the - * specific language governing permissions and limitations - * under the License. - * - */ - -#include "qpid/sys/Mutex.h" -#include <boost/noncopyable.hpp> - -namespace qpid { -namespace sys { - -class Mutex; - -/** - * LockPtr is a smart pointer to T. It is constructed from a volatile - * T* and a Lock (by default a Mutex). It const_casts away the - * volatile qualifier and locks the Lock for the duration of its - * - * Used in conjuntion with the "volatile" keyword to get the compiler - * to help enforce correct concurrent use of mutli-threaded objects. - * See ochttp://www.ddj.com/cpp/184403766 for a detailed discussion. - * - * To summarize the convention: - * - Declare thread-safe member functions as volatile. - * - Declare instances of the class that may be called concurrently as volatile. - * - Use LockPtr to cast away the volatile qualifier while taking a lock. - * - * This means that code calling on a concurrently-used object - * (declared volatile) can only call thread-safe (volatile) member - * functions. Code that needs to use thread-unsafe members must use a - * LockPtr, thereby acquiring the lock and making it safe to do so. - * - * A good type-safe pattern is the internally-locked object: - * - It has it's own private lock member. - * - All public functions are thread safe and declared volatile. - * - Any thread-unsafe, non-volatile functions are private. - * - Only member function implementations use LockPtr to access private functions. - * - * This encapsulates all the locking logic inside the class. - * - * One nice feature of this convention is the common case where you - * need a public, locked version of some function foo() and also a - * private unlocked version to avoid recursive locks. They can be declared as - * volatile and non-volatile overloads of the same function: - * - * // public - * void Thing::foo() volatile { LockPtr<Thing>(this, myLock)->foo(); } - * // private - * void Thing::foo() { ... do stuff ...} - */ - -template <class T, class Lock> class LockPtr : public boost::noncopyable { - public: - LockPtr(volatile T* p, Lock& l) : ptr(const_cast<T*>(p)), lock(l) { lock.lock(); } - LockPtr(volatile T* p, volatile Lock& l) : ptr(const_cast<T*>(p)), lock(const_cast<Lock&>(l)) { lock.lock(); } - ~LockPtr() { lock.unlock(); } - - T& operator*() { return *ptr; } - T* operator->() { return ptr; } - - private: - T* ptr; - Lock& lock; -}; - - -}} // namespace qpid::sys - - -#endif /*!QPID_SYS_LOCKPTR_H*/ |