common/seed.cpp

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/***************************************************************************
 *  common/seed.cpp
 *
 *  Part of the STXXL. See http://stxxl.sourceforge.net
 *
 *  Copyright (C) 2007, 2008 Andreas Beckmann <beckmann@cs.uni-frankfurt.de>
 *  Copyright (C) 2008 Roman Dementiev <dementiev@ira.uka.de>
 *
 *  Distributed under the Boost Software License, Version 1.0.
 *  (See accompanying file LICENSE_1_0.txt or copy at
 *  http://www.boost.org/LICENSE_1_0.txt)
 **************************************************************************/

#include <cassert>
#include <ctime>
#ifdef STXXL_BOOST_CONFIG
 #include <boost/config.hpp>
#endif
#ifdef BOOST_MSVC
 #include <io.h>
 #include <windows.h>
#else
 #include <unistd.h>
 #include <sys/time.h>
#endif

#include <stxxl/bits/common/seed.h>
#include <stxxl/bits/common/mutex.h>


__STXXL_BEGIN_NAMESPACE

inline unsigned initial_seed();

struct seed_generator_t {
    unsigned seed;
    mutex mtx;

    seed_generator_t(unsigned s) : seed(s)
    { }
};

seed_generator_t & seed_generator()
{
    static seed_generator_t sg(initial_seed());
    return sg;
}

inline unsigned initial_seed()
{
    static bool initialized = false;
    assert(!initialized); // this should only be called once!

    initialized = true;
#ifdef BOOST_MSVC
    // GetTickCount():  ms since system start
    return GetTickCount() ^ GetCurrentProcessId();
#else
    struct timeval tv;
    gettimeofday(&tv, 0);

    return tv.tv_sec ^ tv.tv_usec ^ (getpid() << 16);
#endif
}

void set_seed(unsigned seed)
{
    scoped_mutex_lock Lock(seed_generator().mtx);
    seed_generator().seed = seed;
}

unsigned get_next_seed()
{
    scoped_mutex_lock Lock(seed_generator().mtx);
    return seed_generator().seed++;
}

__STXXL_END_NAMESPACE