181 lines
3.9 KiB
C++
181 lines
3.9 KiB
C++
#pragma once
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/*
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* Copyright (c) 2016 MariaDB Corporation Ab
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*
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* Use of this software is governed by the Business Source License included
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* in the LICENSE.TXT file and at www.mariadb.com/bsl11.
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*
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* Change Date: 2019-07-01
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*
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* On the date above, in accordance with the Business Source License, use
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* of this software will be governed by version 2 or later of the General
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* Public License.
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*/
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#include <maxscale/cppdefs.hh>
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#include <stdio.h>
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namespace maxscale
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{
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/**
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* @class CloserTraits utils.hh <maxscale/utils.hh>
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*
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* A traits class used by Closer. To be specialized for all types that are
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* used with Closer.
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*/
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template<class T>
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struct CloserTraits
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{
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/**
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* Closes/frees/destroys a resource.
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*
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* @param t Close the resource *if* it has not been closed already.
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*/
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static void close_if(T t);
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/**
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* Resets a reference to a resource. After the call, the value of t should
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* be such that @c close_if can recognize that the reference already has
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* been closed.
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*
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* @param t Reference to a resource.
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*/
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static void reset(T& t);
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};
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/**
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* @class Closer utils.hh <maxscale/utils.hh>
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*
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* The template class Closer is a class that is intended to be used
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* for ensuring that a C style resource is released at the end of a
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* scoped block, irrespective of how that block is exited (by reaching
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* the end of it, or by a return or exception in the middle of it).
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*
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* Closer performs the actual resource releasing using CloserTraits
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* that need to be specialized for every type of resource to be managed.
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*
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* Example:
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* @code
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* void f()
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* {
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* FILE* pFile = fopen(...);
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*
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* if (pFile)
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* {
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* Closer<FILE*> file(pFile);
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*
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* // Use pFile, call functions that potentually may throw
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* }
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* }
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* @endcode
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*
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* Without @c Closer all code would have to be placed within try/catch
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* blocks, which quickly becomes unwieldy as the number of managed
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* resources grows.
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*/
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template<class T>
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class Closer
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{
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public:
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/**
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* Creates the closer and stores the provided resourece. Note that
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* the constructor assumes that the resource exists already.
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*
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* @param resource The resource whose closing is to be ensured.
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*/
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Closer(T resource)
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: m_resource(resource)
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{
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}
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/**
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* Destroys the closer and releases the resource.
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*/
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~Closer()
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{
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CloserTraits<T>::close_if(m_resource);
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}
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/**
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* Returns the original resource. Note that the ownership of the
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* resource remains with the closer.
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*
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* @return The resource that was provided in the constructor.
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*/
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T get() const
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{
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return m_resource;
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}
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/**
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* Resets the closer, that is, releases the resource.
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*/
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void reset()
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{
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CloserTraits<T>::close_if(m_resource);
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CloserTraits<T>::reset(m_resource);
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}
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/**
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* Resets the closer, that is, releases the resource and assigns a
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* new resource to it.
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*/
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void reset(T resource)
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{
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CloserTraits<T>::close_if(m_resource);
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m_resource = resource;
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}
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/**
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* Returns the original resource together with its ownership. That is,
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* after this call the responsibility for releasing the resource belongs
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* to the caller.
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*
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* @return The resource that was provided in the constructor.
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*/
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T release()
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{
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T resource = m_resource;
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CloserTraits<T>::reset(m_resource);
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return resource;
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}
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private:
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Closer(const Closer&);
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Closer& operator = (const Closer&);
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private:
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T m_resource;
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};
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}
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namespace maxscale
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{
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/**
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* @class CloserTraits<FILE*> utils.hh <maxscale/utils.hh>
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*
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* Specialization of @c CloserTraits for @c FILE*.
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*/
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template<>
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struct CloserTraits<FILE*>
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{
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static void close_if(FILE* pFile)
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{
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if (pFile)
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{
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fclose(pFile);
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}
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}
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static void reset(FILE*& pFile)
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{
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pFile = NULL;
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}
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};
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}
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