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89 lines
3.5 KiB
C++
89 lines
3.5 KiB
C++
#ifndef BOOST_DETAIL_LIGHTWEIGHT_MUTEX_HPP_INCLUDED
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#define BOOST_DETAIL_LIGHTWEIGHT_MUTEX_HPP_INCLUDED
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#if _MSC_VER >= 1020
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#pragma once
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#endif
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//
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// boost/detail/lightweight_mutex.hpp - lightweight mutex
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//
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// Copyright (c) 2002 Peter Dimov and Multi Media Ltd.
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//
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// Permission to copy, use, modify, sell and distribute this software
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// is granted provided this copyright notice appears in all copies.
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// This software is provided "as is" without express or implied
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// warranty, and with no claim as to its suitability for any purpose.
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//
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// typedef <unspecified> boost::detail::lightweight_mutex;
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//
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// boost::detail::lightweight_mutex meets a subset of the Mutex concept
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// requirements: http://www.boost.org/libs/thread/doc/mutex_concept.html#Mutex
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//
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// * Used by the smart pointer library
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// * Performance oriented
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// * Header-only implementation
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// * Small memory footprint
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// * Not a general purpose mutex, use boost::mutex, CRITICAL_SECTION or
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// pthread_mutex instead.
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// * Never spin in a tight lock/do-something/unlock loop, since
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// lightweight_mutex does not guarantee fairness.
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// * Never keep a lightweight_mutex locked for long periods.
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//
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// The current implementation can use a pthread_mutex, a CRITICAL_SECTION,
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// or a platform-specific spinlock.
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//
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// You can force a particular implementation by defining BOOST_LWM_USE_PTHREADS,
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// BOOST_LWM_USE_CRITICAL_SECTION, or BOOST_LWM_USE_SPINLOCK.
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//
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// If neither macro has been defined, the default is to use a spinlock on Win32,
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// and a pthread_mutex otherwise.
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//
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// Note that a spinlock is not a general synchronization primitive. In particular,
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// it is not guaranteed to be a memory barrier, and it is possible to "livelock"
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// if a lower-priority thread has acquired the spinlock but a higher-priority
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// thread is spinning trying to acquire the same lock.
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//
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// For these reasons, spinlocks have been disabled by default except on Windows,
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// where a spinlock can be several orders of magnitude faster than a CRITICAL_SECTION.
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// Note: lwm_linux.hpp has been disabled by default; see the comments
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// inside for more info.
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#include <boost/config.hpp>
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// Note to implementors: if you write a platform-specific spinlock
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// for a platform that supports pthreads, be sure to test its performance
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// against the pthreads-based version using shared_ptr_timing_test.cpp and
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// shared_ptr_mt_test.cpp. Custom versions are usually not worth the trouble
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// _unless_ the performance gains are substantial.
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//
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// Be sure to compare against a "real" pthreads library;
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// shared_ptr_timing_test.cpp will compile succesfully with a stub do-nothing
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// pthreads library, since it doesn't create any threads.
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#ifndef BOOST_HAS_THREADS
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# include <boost/detail/lwm_nop.hpp>
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#elif defined(BOOST_LWM_USE_SPINLOCK) && defined(BOOST_USE_ASM_ATOMIC_H)
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# include <boost/detail/lwm_linux.hpp>
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#elif defined(BOOST_LWM_USE_CRITICAL_SECTION)
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# include <boost/detail/lwm_win32_cs.hpp>
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#elif defined(BOOST_LWM_USE_PTHREADS)
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# include <boost/detail/lwm_pthreads.hpp>
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#elif defined(WIN32) || defined(_WIN32) || defined(__WIN32__)
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# include <boost/detail/lwm_win32.hpp>
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#elif defined(BOOST_LWM_USE_SPINLOCK) && defined(__sgi)
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# include <boost/detail/lwm_irix.hpp>
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#elif defined(BOOST_LWM_USE_SPINLOCK) && defined(__GLIBCPP__)
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# include <boost/detail/lwm_gcc.hpp>
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#elif defined(BOOST_HAS_PTHREADS)
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# define BOOST_LWM_USE_PTHREADS
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# include <boost/detail/lwm_pthreads.hpp>
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#else
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# include <boost/detail/lwm_nop.hpp>
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#endif
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#endif // #ifndef BOOST_DETAIL_LIGHTWEIGHT_MUTEX_HPP_INCLUDED
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