_threads.c

MONA是为数不多的C++语言编写的一个很小的操作系统

/*
 *
 *
 * Copyright (c) 1994
 * Hewlett-Packard Company
 *
 * Copyright (c) 1996,1997
 * Silicon Graphics Computer Systems, Inc.
 *
 * Copyright (c) 1997
 * Moscow Center for SPARC Technology
 *
 * Copyright (c) 1999 
 * Boris Fomitchev
 *
 * This material is provided "as is", with absolutely no warranty expressed
 * or implied. Any use is at your own risk.
 *
 * Permission to use or copy this software for any purpose is hereby granted 
 * without fee, provided the above notices are retained on all copies.
 * Permission to modify the code and to distribute modified code is granted,
 * provided the above notices are retained, and a notice that the code was
 * modified is included with the above copyright notice.
 *
 */
#ifndef _STLP_THREADS_C
#define _STLP_THREADS_C

#ifndef _STLP_INTERNAL_THREADS_H
# include <stl/_threads.h>
#endif

# if defined (_STLP_EXPOSE_GLOBALS_IMPLEMENTATION)

# if defined(_STLP_SGI_THREADS)
#  include <time.h>
# elif defined (_STLP_UNIX)
#  include <ctime>
# if defined (_STLP_USE_NAMESPACES) && ! defined (_STLP_VENDOR_GLOBAL_CSTD)
using _STLP_VENDOR_CSTD::time_t;
# endif
#  include <sys/time.h>
# endif

_STLP_BEGIN_NAMESPACE

# if (_STLP_STATIC_TEMPLATE_DATA > 0)

#  ifdef _STLP_THREADS
#  if !defined(_STLP_ATOMIC_EXCHANGE) && (defined(_STLP_PTHREADS) || defined(_STLP_UITHREADS) || defined(_STLP_OS2THREADS) || defined(_STLP_USE_PTHREAD_SPINLOCK))
template<int __dummy>
_STLP_STATIC_MUTEX
_Swap_lock_struct<__dummy>::_S_swap_lock _STLP_MUTEX_INITIALIZER;
#  endif
#  endif //_STLP_THREADS

#  ifndef _STLP_USE_PTHREAD_SPINLOCK
template <int __inst>
unsigned _STLP_mutex_spin<__inst>::__max = _STLP_mutex_spin<__inst>::__low_max;

template <int __inst>
unsigned _STLP_mutex_spin<__inst>::__last = 0;
#  endif // _STLP_USE_PTHREAD_SPINLOCK

# else /* ( _STLP_STATIC_TEMPLATE_DATA > 0 ) */

#  if defined(_STLP_PTHREADS) || defined(_STLP_UITHREADS) || defined(_STLP_OS2THREADS)
__DECLARE_INSTANCE(_STLP_STATIC_MUTEX, _Swap_lock_struct<0>::_S_swap_lock, 
                   _STLP_MUTEX_INITIALIZER  );
#  endif /* _STLP_PTHREADS */

#  ifndef _STLP_USE_PTHREAD_SPINLOCK
__DECLARE_INSTANCE(unsigned, _STLP_mutex_spin<0>::__max,  =30);
__DECLARE_INSTANCE(unsigned, _STLP_mutex_spin<0>::__last, =0);
#  endif // _STLP_USE_PTHREAD_SPINLOCK

# endif /* ( _STLP_STATIC_TEMPLATE_DATA > 0 ) */

#ifndef _STLP_USE_PTHREAD_SPINLOCK

#ifdef _STLP_SPARC_SOLARIS_THREADS
// underground function in libc.so; we do not want dependance on librt
extern "C" int __nanosleep(const struct timespec*, struct timespec*);
# define _STLP_NANOSLEEP __nanosleep
#else
# define _STLP_NANOSLEEP nanosleep
#endif

template <int __inst>
void _STLP_CALL
_STLP_mutex_spin<__inst>::_S_nsec_sleep(int __log_nsec) {
#     if defined(_STLP_WIN32THREADS)
	  if (__log_nsec <= 20) {
        // Note from boost (www.boost.org): 
        // Changed to Sleep(1) from Sleep(0).
        // According to MSDN, Sleep(0) will never yield
        // to a lower-priority thread, whereas Sleep(1)
        // will. Performance seems not to be affected.
	      Sleep(1);
	  } else {
	      Sleep(1 << (__log_nsec - 20));
	  }
#    elif defined(_STLP_OS2THREADS)
      if (__log_nsec <= 20) {
         DosSleep(0);
      } else {
         DosSleep(1 << (__log_nsec - 20));
      }
#     elif defined (_STLP_UNIX)
          timespec __ts;
          /* Max sleep is 2**27nsec ~ 60msec      */
          __ts.tv_sec = 0;
          __ts.tv_nsec = 1 << __log_nsec;
          _STLP_NANOSLEEP(&__ts, 0);
#     endif
  }


template <int __inst>
void  _STLP_CALL
_STLP_mutex_spin<__inst>::_M_do_lock(volatile __stl_atomic_t* __lock)
{
#if defined(_STLP_ATOMIC_EXCHANGE)
  if (_Atomic_swap(__lock, 1)) {
    unsigned __my_spin_max = _STLP_mutex_spin<0>::__max;
    unsigned __my_last_spins = _STLP_mutex_spin<0>::__last;
    volatile unsigned __junk = 17; 	// Value doesn't matter.
    unsigned  __i;
    
    for (__i = 0; __i < __my_spin_max; ++__i) {
      if (__i < __my_last_spins/2 || *__lock) {
        __junk *= __junk; __junk *= __junk;
        __junk *= __junk; __junk *= __junk;
      } else {
        if (!_Atomic_swap(__lock, 1)) {
          // got it!
          // Spinning worked.  Thus we're probably not being scheduled
          // against the other process with which we were contending.
          // Thus it makes sense to spin longer the next time.
          _STLP_mutex_spin<0>::__last = __i;
          _STLP_mutex_spin<0>::__max = _STLP_mutex_spin<0>::__high_max;
	    return;
        }
      }
    }
    
    // We are probably being scheduled against the other process.  Sleep.
    _STLP_mutex_spin<0>::__max = _STLP_mutex_spin<0>::__low_max;
    
    for (__i = 0 ;; ++__i) {
      int __log_nsec = __i + 6;
      
      if (__log_nsec > 27) __log_nsec = 27;
      if (!_Atomic_swap(__lock, 1)) {
	  break;
      }
      _S_nsec_sleep(__log_nsec);
    }
    
  } /* first _Atomic_swap */
# endif
}
#endif // _STLP_USE_PTHREAD_SPINLOCK

_STLP_END_NAMESPACE

# endif /* BUILDING_STLPORT */
#endif /*  _STLP_THREADS_C */

// Local Variables:
// mode:C++
// End: