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Posted 27 Sep 2004

Smart Pointers to boost your code

, 27 Sep 2004
A beginner's introduction to the smart pointers provided by the boost library.

// MS compatible compilers support #pragma once

#if defined(_MSC_VER) && (_MSC_VER >= 1020)
# pragma once

//  boost/detail/lightweight_mutex.hpp - lightweight mutex
//  Copyright (c) 2002, 2003 Peter Dimov and Multi Media Ltd.
//  Permission to copy, use, modify, sell and distribute this software
//  is granted provided this copyright notice appears in all copies.
//  This software is provided "as is" without express or implied
//  warranty, and with no claim as to its suitability for any purpose.
//  typedef <unspecified> boost::detail::lightweight_mutex;
//  boost::detail::lightweight_mutex meets a subset of the Mutex concept
//  requirements:
//  * Used by the smart pointer library
//  * Performance oriented
//  * Header-only implementation
//  * Small memory footprint
//  * Not a general purpose mutex, use boost::mutex, CRITICAL_SECTION or
//    pthread_mutex instead.
//  * Never spin in a tight lock/do-something/unlock loop, since
//    lightweight_mutex does not guarantee fairness.
//  * Never keep a lightweight_mutex locked for long periods.
//  The current implementation can use a pthread_mutex, a CRITICAL_SECTION,
//  or a platform-specific spinlock.
//  You can force a particular implementation by defining BOOST_LWM_USE_PTHREADS,
//  If neither macro has been defined, the default is to use a spinlock on Win32,
//  and a pthread_mutex otherwise.
//  Note that a spinlock is not a general synchronization primitive. In particular,
//  it is not guaranteed to be a memory barrier, and it is possible to "livelock"
//  if a lower-priority thread has acquired the spinlock but a higher-priority
//  thread is spinning trying to acquire the same lock.
//  For these reasons, spinlocks have been disabled by default except on Windows,
//  where a spinlock can be several orders of magnitude faster than a CRITICAL_SECTION.

//  Note: lwm_linux.hpp has been disabled by default; see the comments
//        inside for more info.

#include <boost/config.hpp>

//  Note to implementors: if you write a platform-specific spinlock
//  for a platform that supports pthreads, be sure to test its performance
//  against the pthreads-based version using shared_ptr_timing_test.cpp and
//  shared_ptr_mt_test.cpp. Custom versions are usually not worth the trouble
//  _unless_ the performance gains are substantial.
//  Be sure to compare against a "real" pthreads library;
//  shared_ptr_timing_test.cpp will compile succesfully with a stub do-nothing
//  pthreads library, since it doesn't create any threads.

#if (defined(WIN32) || defined(_WIN32) || defined(__WIN32__)) && !defined(BOOST_LWM_USE_CRITICAL_SECTION) && !defined(BOOST_LWM_USE_PTHREADS)
# define BOOST_LWM_WIN32

#if !defined(BOOST_HAS_THREADS)
#  if defined(BOOST_LWM_WIN32)
#    include <boost/detail/lwm_win32_nt.hpp>
#  else
#    include <boost/detail/lwm_nop.hpp>
#  endif
#  include <boost/detail/lwm_linux.hpp>
#  include <boost/detail/lwm_win32_cs.hpp>
#  include <boost/detail/lwm_pthreads.hpp>
#elif defined(BOOST_LWM_WIN32)
#  include <boost/detail/lwm_win32.hpp>
#elif defined(BOOST_LWM_USE_SPINLOCK) && defined(__sgi)
#  include <boost/detail/lwm_irix.hpp>
#elif defined(BOOST_LWM_USE_SPINLOCK) && defined(__GLIBCPP__)
#  include <boost/detail/lwm_gcc.hpp>
#elif defined(BOOST_HAS_PTHREADS)
#  include <boost/detail/lwm_pthreads.hpp>
// Use #define BOOST_DISABLE_THREADS to avoid the error
#  error Unrecognized threading platform


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About the Author

Germany Germany
Peter is tired of being called "Mr. Chen", even so certain individuals insist on it. No, he's not chinese.

Peter has seen lots of boxes you youngsters wouldn't even accept as calculators. He is proud of having visited the insides of a 16 Bit Machine.

In his spare time he ponders new ways of turning groceries into biohazards, or tries to coax South American officials to add some stamps to his passport.

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