boost/boost/detail/lightweight_mutex.hpp

   1 #ifndef BOOST_DETAIL_LIGHTWEIGHT_MUTEX_HPP_INCLUDED
   2 #define BOOST_DETAIL_LIGHTWEIGHT_MUTEX_HPP_INCLUDED
   3
   4 #if _MSC_VER >= 1020
   5 #pragma once
   6 #endif
   7
   8 //
   9 //  boost/detail/lightweight_mutex.hpp - lightweight mutex
  10 //
  11 //  Copyright (c) 2002 Peter Dimov and Multi Media Ltd.
  12 //
  13 //  Permission to copy, use, modify, sell and distribute this software
  14 //  is granted provided this copyright notice appears in all copies.
  15 //  This software is provided "as is" without express or implied
  16 //  warranty, and with no claim as to its suitability for any purpose.
  17 //
  18 //  typedef <unspecified> boost::detail::lightweight_mutex;
  19 //
  20 //  boost::detail::lightweight_mutex meets a subset of the Mutex concept
  21 //  requirements: http://www.boost.org/libs/thread/doc/mutex_concept.html#Mutex
  22 //
  23 //  * Used by the smart pointer library
  24 //  * Performance oriented
  25 //  * Header-only implementation
  26 //  * Small memory footprint
  27 //  * Not a general purpose mutex, use boost::mutex, CRITICAL_SECTION or
  28 //    pthread_mutex instead.
  29 //  * Never spin in a tight lock/do-something/unlock loop, since
  30 //    lightweight_mutex does not guarantee fairness.
  31 //  * Never keep a lightweight_mutex locked for long periods.
  32 //
  33 //  The current implementation can use a pthread_mutex, a CRITICAL_SECTION,
  34 //  or a platform-specific spinlock.
  35 //
  36 //  You can force a particular implementation by defining BOOST_LWM_USE_PTHREADS,
  37 //  BOOST_LWM_USE_CRITICAL_SECTION, or BOOST_LWM_USE_SPINLOCK.
  38 //
  39 //  If neither macro has been defined, the default is to use a spinlock on Win32,
  40 //  and a pthread_mutex otherwise.
  41 //
  42 //  Note that a spinlock is not a general synchronization primitive. In particular,
  43 //  it is not guaranteed to be a memory barrier, and it is possible to "livelock"
  44 //  if a lower-priority thread has acquired the spinlock but a higher-priority
  45 //  thread is spinning trying to acquire the same lock.
  46 //
  47 //  For these reasons, spinlocks have been disabled by default except on Windows,
  48 //  where a spinlock can be several orders of magnitude faster than a CRITICAL_SECTION.
  49
  50
  51 //  Note: lwm_linux.hpp has been disabled by default; see the comments
  52 //        inside for more info.
  53
  54
  55 #include <boost/config.hpp>
  56
  57 //  Note to implementors: if you write a platform-specific spinlock
  58 //  for a platform that supports pthreads, be sure to test its performance
  59 //  against the pthreads-based version using shared_ptr_timing_test.cpp and
  60 //  shared_ptr_mt_test.cpp. Custom versions are usually not worth the trouble
  61 //  _unless_ the performance gains are substantial.
  62 //
  63 //  Be sure to compare against a "real" pthreads library;
  64 //  shared_ptr_timing_test.cpp will compile succesfully with a stub do-nothing
  65 //  pthreads library, since it doesn't create any threads.
  66
  67 #ifndef BOOST_HAS_THREADS
  68 #  include <boost/detail/lwm_nop.hpp>
  69 #elif defined(BOOST_LWM_USE_SPINLOCK) && defined(BOOST_USE_ASM_ATOMIC_H)
  70 #  include <boost/detail/lwm_linux.hpp>
  71 #elif defined(BOOST_LWM_USE_CRITICAL_SECTION)
  72 #  include <boost/detail/lwm_win32_cs.hpp>
  73 #elif defined(BOOST_LWM_USE_PTHREADS)
  74 #  include <boost/detail/lwm_pthreads.hpp>
  75 #elif defined(WIN32) || defined(_WIN32) || defined(__WIN32__)
  76 #  include <boost/detail/lwm_win32.hpp>
  77 #elif defined(BOOST_LWM_USE_SPINLOCK) && defined(__sgi)
  78 #  include <boost/detail/lwm_irix.hpp>
  79 #elif defined(BOOST_LWM_USE_SPINLOCK) && defined(__GLIBCPP__)
  80 #  include <boost/detail/lwm_gcc.hpp>
  81 #elif defined(BOOST_HAS_PTHREADS)
  82 #  define BOOST_LWM_USE_PTHREADS
  83 #  include <boost/detail/lwm_pthreads.hpp>
  84 #else
  85 // Use #define BOOST_DISABLE_THREADS to avoid the error
  86 #  error Unrecognized threading platform
  87 #endif
  88
  89 #endif // #ifndef BOOST_DETAIL_LIGHTWEIGHT_MUTEX_HPP_INCLUDED