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312 lines
8.8 KiB
C++
312 lines
8.8 KiB
C++
/*============================================================================*/
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/*
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VFLib: https://github.com/vinniefalco/VFLib
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Copyright (C) 2008 by Vinnie Falco <vinnie.falco@gmail.com>
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This library contains portions of other open source products covered by
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separate licenses. Please see the corresponding source files for specific
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terms.
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VFLib is provided under the terms of The MIT License (MIT):
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Permission is hereby granted, free of charge, to any person obtaining a copy
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of this software and associated documentation files (the "Software"), to deal
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in the Software without restriction, including without limitation the rights
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to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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copies of the Software, and to permit persons to whom the Software is
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furnished to do so, subject to the following conditions:
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The above copyright notice and this permission notice shall be included in
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all copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
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FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
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IN THE SOFTWARE.
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*/
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/*============================================================================*/
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#ifndef BEAST_CONCURRENTSTATE_BEASTHEADER
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#define BEAST_CONCURRENTSTATE_BEASTHEADER
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/*============================================================================*/
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/**
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Structured access to a shared state.
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This template wraps an object containing members representing state
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information shared between multiple threads of execution, where any thread
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may need to read or write as needed. Synchronized access to the concurrent
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state is enforced at compile time through strongly typed accessor classes.
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This interface design facilitates source code pattern matching to find all
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areas where a concurrent state is accessed.
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There are three types of access:
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- ReadAccess
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Allows read access to the underlying object as `const`. ReadAccess may be
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granted to one or more threads simultaneously. If one or more threads have
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ReadAccess, requests to obtain WriteAccess are blocked.
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- WriteAccess
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Allows exclusive read/write access the underlying object. A WriteAccess
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request blocks until all existing ReadAccess and WriteAccess requests are
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released. While a WriteAccess exists, requests for ReadAccess will block.
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- UnlockedAccess
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Allows read access to the underlying object without using the lock. This
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can be helpful when designing concurrent structures through composition.
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It also makes it easier to search for places in code which use unlocked
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access.
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This code example demonstrates various forms of access to a ConcurrentState:
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@code
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struct SharedData
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{
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int value1;
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String value2;
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};
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typedef ConcurrentState <SharedData> SharedState;
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SharedState sharedState;
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void readExample ()
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{
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SharedState::ReadAccess state (sharedState);
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print (state->value1); // read access
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print (state->value2); // read access
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state->value1 = 42; // write disallowed: compile error
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}
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void writeExample ()
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{
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SharedState::WriteAccess state (sharedState);
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state->value2 = "Label"; // write access
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}
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@endcode
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Forwarding constructors with up to eight parameters are provided. This lets
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you write constructors into the underlying data object. For example:
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@code
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struct SharedData
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{
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explicit SharedData (int numSlots)
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{
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m_array.reserve (numSlots);
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}
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std::vector <AudioSampleBuffer*> m_array;
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};
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// Construct SharedData with one parameter
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ConcurrentState <SharedData> sharedState (16);
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@endcode
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@param Object The type of object to encapsulate.
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@warning Recursive calls are not supported. It is generally not possible for
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a thread of execution to acquire write access while it already has
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read access. Such an attempt will result in undefined behavior. Calling into
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unknown code while holding a lock can cause deadlock. See
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@ref CallQueue::queue().
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@ingroup beast_concurrent
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*/
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template <class Object>
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class ConcurrentState : Uncopyable
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{
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public:
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class ReadAccess;
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class WriteAccess;
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class UnlockedAccess;
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/** Create a concurrent state.
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Up to 8 parameters can be specified in the constructor. These parameters
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are forwarded to the corresponding constructor in Object. If no
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constructor in Object matches the parameter list, a compile error is
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generated.
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*/
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/** @{ */
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ConcurrentState () { }
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template <class T1>
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explicit ConcurrentState (T1 t1)
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: m_obj (t1) { }
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template <class T1, class T2>
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ConcurrentState (T1 t1, T2 t2)
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: m_obj (t1, t2) { }
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template <class T1, class T2, class T3>
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ConcurrentState (T1 t1, T2 t2, T3 t3)
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: m_obj (t1, t2, t3) { }
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template <class T1, class T2, class T3, class T4>
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ConcurrentState (T1 t1, T2 t2, T3 t3, T4 t4)
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: m_obj (t1, t2, t3, t4) { }
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template <class T1, class T2, class T3, class T4, class T5>
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ConcurrentState (T1 t1, T2 t2, T3 t3, T4 t4, T5 t5)
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: m_obj (t1, t2, t3, t4, t5) { }
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template <class T1, class T2, class T3, class T4, class T5, class T6>
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ConcurrentState (T1 t1, T2 t2, T3 t3, T4 t4, T5 t5, T6 t6)
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: m_obj (t1, t2, t3, t4, t5, t6) { }
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template <class T1, class T2, class T3, class T4, class T5, class T6, class T7>
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ConcurrentState (T1 t1, T2 t2, T3 t3, T4 t4, T5 t5, T6 t6, T7 t7) : m_obj (t1, t2, t3, t4, t5, t6, t7) { }
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template <class T1, class T2, class T3, class T4, class T5, class T6, class T7, class T8>
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ConcurrentState (T1 t1, T2 t2, T3 t3, T4 t4, T5 t5, T6 t6, T7 t7, T8 t8)
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: m_obj (t1, t2, t3, t4, t5, t6, t7, t8) { }
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/** @} */
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private:
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typedef ReadWriteMutex ReadWriteMutexType;
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Object m_obj;
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ReadWriteMutexType m_mutex;
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};
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//------------------------------------------------------------------------------
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/** Unlocked access to a ConcurrentState.
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Use sparingly.
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*/
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template <class Object>
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class ConcurrentState <Object>::UnlockedAccess : Uncopyable
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{
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public:
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explicit UnlockedAccess (ConcurrentState const& state)
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: m_state (state)
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{
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}
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Object const& getObject () const
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{
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return m_state.m_obj;
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}
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Object const& operator* () const
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{
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return getObject ();
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}
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Object const* operator-> () const
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{
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return &getObject ();
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}
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private:
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ConcurrentState const& m_state;
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};
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//------------------------------------------------------------------------------
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/** Read only access to a ConcurrentState */
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template <class Object>
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class ConcurrentState <Object>::ReadAccess : Uncopyable
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{
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public:
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/** Create a ReadAccess from the specified ConcurrentState */
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explicit ReadAccess (ConcurrentState const volatile& state)
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: m_state (const_cast <ConcurrentState const&> (state))
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, m_lock (m_state.m_mutex)
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{
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}
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/** Obtain a read only reference to Object */
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Object const& getObject () const
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{
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return m_state.m_obj;
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}
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/** Obtain a read only reference to Object */
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Object const& operator* () const
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{
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return getObject ();
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}
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/** Obtain a read only smart pointer to Object */
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Object const* operator-> () const
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{
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return &getObject ();
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}
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private:
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ConcurrentState const& m_state;
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ReadWriteMutexType::ScopedReadLockType m_lock;
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};
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//------------------------------------------------------------------------------
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/** Read/write access to a ConcurrentState */
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template <class Object>
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class ConcurrentState <Object>::WriteAccess : Uncopyable
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{
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public:
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explicit WriteAccess (ConcurrentState& state)
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: m_state (state)
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, m_lock (m_state.m_mutex)
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{
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}
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/** Obtain a read only reference to Object */
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Object const* getObject () const
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{
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return m_state.m_obj;
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}
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/** Obtain a read only reference to Object */
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Object const& operator* () const
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{
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return getObject ();
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}
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/** Obtain a read only smart pointer to Object */
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Object const* operator-> () const
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{
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return &getObject ();
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}
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/** Obtain a read/write pointer to Object */
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Object& getObject ()
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{
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return m_state.m_obj;
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}
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/** Obtain a read/write reference to Object */
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Object& operator* ()
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{
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return getObject ();
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}
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/** Obtain a read/write smart pointer to Object */
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Object* operator-> ()
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{
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return &getObject ();
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}
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private:
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ConcurrentState& m_state;
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ReadWriteMutexType::ScopedWriteLockType m_lock;
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};
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#endif
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