seed.cpp

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/***************************************************************************
 * lib/common/seed.cpp
 *
 * Part of the STXXL. See http://stxxl.sourceforge.net
 *
 * Copyright (C) 2007, 2008 Andreas Beckmann <[email protected]>
 * Copyright (C) 2008 Roman Dementiev <[email protected]>
 *
 * 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 <stxxl/bits/config.h>
#include <stxxl/bits/common/mutex.h>
#include <stxxl/bits/namespace.h>

#if STXXL_WINDOWS
 #ifndef NOMINMAX
 #define NOMINMAX
 #endif
 #include <io.h>
 #include <windows.h>
#else
 #include <unistd.h>
 #include <sys/time.h>
#endif


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()
{
#ifndef NDEBUG
 static bool initialized = false;
 assert(!initialized); // this should only be called once!

 initialized = true;
#endif // NDEBUG
#if STXXL_WINDOWS
 // 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