ThreadLocal.h

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#ifndef SimTK_SimTKCOMMON_THREAD_LOCAL_H_
#define SimTK_SimTKCOMMON_THREAD_LOCAL_H_

/* -------------------------------------------------------------------------- *
 *                       Simbody(tm): SimTKcommon                             *
 * -------------------------------------------------------------------------- *
 * This is part of the SimTK biosimulation toolkit originating from           *
 * Simbios, the NIH National Center for Physics-Based Simulation of           *
 * Biological Structures at Stanford, funded under the NIH Roadmap for        *
 * Medical Research, grant U54 GM072970. See https://simtk.org/home/simbody.  *
 *                                                                            *
 * Portions copyright (c) 2008-15 Stanford University and the Authors.        *
 * Authors: Peter Eastman                                                     *
 * Contributors: Michael Sherman                                              *
 *                                                                            *
 * Licensed 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 <pthread.h>
#include <map>
#include <set>

namespace SimTK {

template <class T>
class ThreadLocal {
public:
    ThreadLocal() {
        initialize();
    }

    explicit ThreadLocal(const T& defaultValue) : m_defaultValue(defaultValue) {
        initialize();
    }

    ~ThreadLocal() {
        pthread_key_delete(m_key);
    }

    T& upd() {
        T* value = reinterpret_cast<T*>(pthread_getspecific(m_key));
        if (!value) 
            value = createValue();
        return *value;
    }

    const T& get() const {
        T* value = reinterpret_cast<T*>(pthread_getspecific(m_key));
        if (!value) 
            value = createValue();
        return *value;
    }

private:
    // This is a destructor for an object of type T that was allocated for this
    // thread's exclusive use. This will be called at thread termination, from
    // the same thread that allocated this object via the createValue() 
    // method below.
    static void cleanUpThreadLocalStorage(void* value) {
        T* t = reinterpret_cast<T*>(value);
        delete t;
    }

    void initialize() {
        pthread_key_create(&m_key, cleanUpThreadLocalStorage);
    }

    T* createValue() const {
        T* value = new T(m_defaultValue);
        pthread_setspecific(m_key, value);
        return value;
    }

    pthread_key_t   m_key;
    T               m_defaultValue;
};

} // namespace SimTK

#endif // SimTK_SimTKCOMMON_THREAD_LOCAL_H_