base_thread_per.hh

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/*
 * LEGAL:   COPYRIGHT (C) 2007 JIM E. BROOKS
 *          THIS SOURCE CODE IS RELEASED UNDER THE TERMS
 *          OF THE GNU GENERAL PUBLIC LICENSE VERSION 2 (GPL 2).
 *****************************************************************************/

#if COMPILE_THREADS
#ifndef BASE_THREAD_PER_HH
#define BASE_THREAD_PER_HH 1

#include "base_thread_common.hh"

namespace base {

template<typename T>
class PerThreadPtr
{
  // two PerThreadPtrs can't share the same key
public: 
    PerThreadPtr( void )
    {
        PTHREAD_CALL( pthread_key_create( &mKey, 0 ) );
        NewPerThreadVar();
    }

private:
    // Allocate a new thread variable in per-thread memory.
    T* NewPerThreadVar( void )
    {
        // Suballocate thread memory (thread local storage).
        extern void* SuballocateThreadMemory( const uint bytes );  // solves compiling dependency
        void* objMem = SuballocateThreadMemory( sizeof(T) );

        // Use C++ "placement new" to place a new object in per-thread memory.
        T* obj = new (objMem) T;

        // Use a pthreads key to map pointer and this thread.
        PTHREAD_CALL( pthread_setspecific( mKey, obj ) );
        return obj;
    }

public:
    ~PerThreadPtr()
    {
        PTHREAD_CALL( pthread_key_delete( mKey ) );
    }

    T* operator->( void )
    {
        T* threadVar = reinterpret_cast<T*>( pthread_getspecific( mKey ) );
        if ( EX( threadVar != NULL ) )
        {
            return threadVar;
        }
        else
        {
            // pthread_getspecific() returned NULL.
            // This (probably) means a new thread has started,
            // so allocate its own memory block on the heap object.
            return NewPerThreadVar();
        }
    }

    T& operator*( void )
    {
        return *operator->();
    }

    T* PTR( void )
    {
        return operator->();
    }

private:
    pthread_key_t   mKey;
};

} // namespace base

#endif // BASE_THREAD_PER_HH
#endif // COMPILE_THREADS

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