boost/boost/detail/lightweight_mutex.hpp

   1 #ifndef BOOST_DETAIL_LIGHTWEIGHT_MUTEX_HPP_INCLUDED
   2 #define BOOST_DETAIL_LIGHTWEIGHT_MUTEX_HPP_INCLUDED
   3
   4 // MS compatible compilers support #pragma once
   5
   6 #if defined(_MSC_VER) && (_MSC_VER >= 1020)
   7 # pragma once
   8 #endif
   9
  10 //
  11 //  boost/detail/lightweight_mutex.hpp - lightweight mutex
  12 //
  13 //  Copyright (c) 2002, 2003 Peter Dimov and Multi Media Ltd.
  14 //
  15 // Distributed under the Boost Software License, Version 1.0. (See
  16 // accompanying file LICENSE_1_0.txt or copy at
  17 // http://www.boost.org/LICENSE_1_0.txt)
  18 //
  19 //  typedef <unspecified> boost::detail::lightweight_mutex;
  20 //
  21 //  boost::detail::lightweight_mutex meets a subset of the Mutex concept
  22 //  requirements: http://www.boost.org/libs/thread/doc/mutex_concept.html#Mutex
  23 //
  24 //  * Used by the smart pointer library
  25 //  * Performance oriented
  26 //  * Header-only implementation
  27 //  * Small memory footprint
  28 //  * Not a general purpose mutex, use boost::mutex, CRITICAL_SECTION or
  29 //    pthread_mutex instead.
  30 //  * Never spin in a tight lock/do-something/unlock loop, since
  31 //    lightweight_mutex does not guarantee fairness.
  32 //  * Never keep a lightweight_mutex locked for long periods.
  33 //
  34 //  The current implementation can use a pthread_mutex, a CRITICAL_SECTION,
  35 //  or a platform-specific spinlock.
  36 //
  37 //  You can force a particular implementation by defining BOOST_LWM_USE_PTHREADS,
  38 //  BOOST_LWM_USE_CRITICAL_SECTION, or BOOST_LWM_USE_SPINLOCK.
  39 //
  40 //  If neither macro has been defined, the default is to use a spinlock on Win32,
  41 //  and a pthread_mutex otherwise.
  42 //
  43 //  Note that a spinlock is not a general synchronization primitive. In particular,
  44 //  it is not guaranteed to be a memory barrier, and it is possible to "livelock"
  45 //  if a lower-priority thread has acquired the spinlock but a higher-priority
  46 //  thread is spinning trying to acquire the same lock.
  47 //
  48 //  For these reasons, spinlocks have been disabled by default except on Windows,
  49 //  where a spinlock can be several orders of magnitude faster than a CRITICAL_SECTION.
  50
  51
  52 //  Note: lwm_linux.hpp has been disabled by default; see the comments
  53 //        inside for more info.
  54
  55
  56 #include <boost/config.hpp>
  57
  58 //  Note to implementors: if you write a platform-specific spinlock
  59 //  for a platform that supports pthreads, be sure to test its performance
  60 //  against the pthreads-based version using shared_ptr_timing_test.cpp and
  61 //  shared_ptr_mt_test.cpp. Custom versions are usually not worth the trouble
  62 //  _unless_ the performance gains are substantial.
  63 //
  64 //  Be sure to compare against a "real" pthreads library;
  65 //  shared_ptr_timing_test.cpp will compile succesfully with a stub do-nothing
  66 //  pthreads library, since it doesn't create any threads.
  67
  68 #if (defined(WIN32) || defined(_WIN32) || defined(__WIN32__)) && !defined(BOOST_LWM_USE_CRITICAL_SECTION) && !defined(BOOST_LWM_USE_PTHREADS)
  69 # define BOOST_LWM_WIN32
  70 #endif
  71
  72 #if !defined(BOOST_HAS_THREADS)
  73 #  if defined(BOOST_LWM_WIN32)
  74 #    include <boost/detail/lwm_win32_nt.hpp>
  75 #  else
  76 #    include <boost/detail/lwm_nop.hpp>
  77 #  endif
  78 #elif defined(BOOST_LWM_USE_SPINLOCK) && defined(BOOST_USE_ASM_ATOMIC_H)
  79 #  include <boost/detail/lwm_linux.hpp>
  80 #elif defined(BOOST_LWM_USE_CRITICAL_SECTION)
  81 #  include <boost/detail/lwm_win32_cs.hpp>
  82 #elif defined(BOOST_LWM_USE_PTHREADS)
  83 #  include <boost/detail/lwm_pthreads.hpp>
  84 #elif defined(BOOST_LWM_WIN32)
  85 #  include <boost/detail/lwm_win32.hpp>
  86 #elif defined(BOOST_LWM_USE_SPINLOCK) && defined(__sgi)
  87 #  include <boost/detail/lwm_irix.hpp>
  88 #elif defined(BOOST_LWM_USE_SPINLOCK) && defined(__GLIBCPP__)
  89 #  include <boost/detail/lwm_gcc.hpp>
  90 #elif defined(BOOST_HAS_PTHREADS)
  91 #  define BOOST_LWM_USE_PTHREADS
  92 #  include <boost/detail/lwm_pthreads.hpp>
  93 #else
  94 // Use #define BOOST_DISABLE_THREADS to avoid the error
  95 #  error Unrecognized threading platform
  96 #endif
  97
  98 #endif // #ifndef BOOST_DETAIL_LIGHTWEIGHT_MUTEX_HPP_INCLUDED