/usr/include/deal.II/base/thread_local_storage.h is in libdeal.ii-dev 8.4.2-2+b1.
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//
// Copyright (C) 2011 - 2015 by the deal.II authors
//
// This file is part of the deal.II library.
//
// The deal.II library is free software; you can use it, redistribute
// it, and/or modify it under the terms of the GNU Lesser General
// Public License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
// The full text of the license can be found in the file LICENSE at
// the top level of the deal.II distribution.
//
// ---------------------------------------------------------------------
#ifndef dealii__thread_local_storage_h
#define dealii__thread_local_storage_h
#include <deal.II/base/config.h>
#ifdef DEAL_II_WITH_THREADS
# include <tbb/enumerable_thread_specific.h>
#endif
DEAL_II_NAMESPACE_OPEN
/*!@addtogroup threads */
/*@{*/
namespace Threads
{
/**
* @brief A class that provides a separate storage location on each thread
* that accesses the object.
*
* This class offers ways so that every thread that accesses it has its own
* copy of an object of type T. In essence, accessing this object can never
* result in race conditions in multithreaded programs since no other thread
* than the current one can ever access it.
*
* The class builds on the Threading Building Blocks's
* tbb::enumerable_thread_specific class but wraps it in such a way that
* this class can also be used when deal.II is configured not to use threads
* at all -- in that case, this class simply stores a single copy of an
* object of type T.
*
* <h3>Construction and destruction</h3>
*
* Objects of this class can either be default constructed or by providing
* an "exemplar", i.e. an object of type T so that every time we need to
* create a T on a thread that doesn't already have such an object, it is
* copied from the exemplar.
*
* Upon destruction of objects of this class, all T objects that correspond
* to threads that have accessed this object are destroyed. Note that this
* may be before the time when a thread is terminated.
*
* <h3>Access</h3>
*
* The T object stored by this object can be accessed using the get()
* function. It provides a reference to a unique object when accessed from
* different threads. Objects of type T are created lazily, i.e. they are
* only created whenever a thread actually calls get().
*/
template <typename T>
class ThreadLocalStorage
{
public:
/**
* Default constructor. Initialize each thread local object using its
* default constructor.
*/
ThreadLocalStorage ();
/**
* A kind of copy constructor. Initialize each thread local object by
* copying the given object.
*/
explicit ThreadLocalStorage (const T &t);
/**
* Copy constructor. Initialize each thread local object with the
* corresponding object of the given object.
*/
ThreadLocalStorage (const ThreadLocalStorage<T> &t);
/**
* Return a reference to the data stored by this object for the current
* thread this function is called on.
*
* Note that there is no member function get() that is const and returns a
* const reference as one would expect. The reason is that if such a
* member function were called on a thread for which no thread-local
* object has been created yet, then one has to create such an object
* first which would certainly be a non-constant operation. If you need to
* call the get() function for a member variable of a class from a const
* member function, then you need to declare the member variable
* <code>mutable</code> to allow such access.
*/
T &get ();
/**
* Same as above, except that @p exists is set to true if an element was
* already present for the current thread; false otherwise.
*/
T &get (bool &exists);
/**
* Conversion operator that simply converts the thread-local object to the
* data type that it stores. This function is equivalent to calling the
* get() member function; it's purpose is to make the TLS object look more
* like the object it is storing.
*/
operator T &();
/**
* Copy the given argument into the storage space used to represent the
* current thread. Calling this function as <code>tls_data = object</code>
* is equivalent to calling <code>tls_data.get() = object</code>. The
* intent of this operator is to make the ThreadLocalStorage object look
* more like the object it represents on the current thread.
*
* @param t The object to be copied into the storage space used for the
* current thread.
*
* @return The current object, after the changes have been made
*/
ThreadLocalStorage<T> &operator = (const T &t);
/**
* Remove the thread-local objects stored for all threads that have
* created one with this object (i.e., that have called get() at least
* once on this thread. This includes the current thread. If you call
* get() subsequently on this or any other thread, new objects will again
* be created.
*
* If deal.II has been configured to not use multithreading, then this
* function does not do anything at all. Note that this of course has
* different semantics as in the multithreading context the objects are
* deleted and created again (possible by copying from a sample object, if
* the appropriate constructor of this class was called), whereas in the
* multithreaded context the object is simply not touched at all. At the
* same time, the purpose of this function is to release memory other
* threads may have allocated for their own thread local objects after
* which every use of this object will require some kind of
* initialization. This is necessary both in the multithreaded or non-
* multithreaded case.
*/
void clear ();
/**
* Returns a reference to the internal Threading Building Blocks
* implementation. This function is really only useful if deal.II has been
* configured with multithreading and has no useful purpose otherwise.
*/
#ifdef DEAL_II_WITH_THREADS
tbb::enumerable_thread_specific<T> &
#else
T &
#endif
get_implementation();
private:
#ifdef DEAL_II_WITH_THREADS
/**
* The data element we store. If we support threads, then this object will
* be of a type that provides a separate object for each thread.
* Otherwise, it is simply a single object of type T.
*/
tbb::enumerable_thread_specific<T> data;
#else
T data;
#endif
};
// ----------------- inline and template functions ----------------------------
template <typename T>
inline
ThreadLocalStorage<T>::ThreadLocalStorage()
{}
template <typename T>
inline
ThreadLocalStorage<T>::ThreadLocalStorage(const T &t)
:
data (t)
{}
template <typename T>
inline
ThreadLocalStorage<T>::ThreadLocalStorage(const ThreadLocalStorage<T> &t)
:
data (t)
{}
template <typename T>
inline
T &
ThreadLocalStorage<T>::get ()
{
#ifdef DEAL_II_WITH_THREADS
return data.local();
#else
return data;
#endif
}
template <typename T>
inline
T &
ThreadLocalStorage<T>::get (bool &exists)
{
#ifdef DEAL_II_WITH_THREADS
return data.local(exists);
#else
exists = true;
return data;
#endif
}
template <typename T>
inline
ThreadLocalStorage<T>::operator T &()
{
return get();
}
template <typename T>
inline
ThreadLocalStorage<T> &
ThreadLocalStorage<T>::operator = (const T &t)
{
get() = t;
return *this;
}
template <typename T>
inline
#ifdef DEAL_II_WITH_THREADS
tbb::enumerable_thread_specific<T> &
#else
T &
#endif
ThreadLocalStorage<T>::get_implementation()
{
return data;
}
template <typename T>
inline
void
ThreadLocalStorage<T>::clear ()
{
#ifdef DEAL_II_WITH_THREADS
data.clear ();
#endif
}
} // end of implementation of namespace Threads
/**
* @}
*/
//---------------------------------------------------------------------------
DEAL_II_NAMESPACE_CLOSE
// end of #ifndef dealii__thread_local_storage_h
#endif
//---------------------------------------------------------------------------
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