/usr/include/boost/interprocess/sync/spin/mutex.hpp is in libboost1.55-dev 1.55.0+dfsg-3.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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//
// (C) Copyright Ion Gaztanaga 2005-2012. Distributed under the Boost
// Software License, Version 1.0. (See accompanying file
// LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
// See http://www.boost.org/libs/interprocess for documentation.
//
//////////////////////////////////////////////////////////////////////////////
#ifndef BOOST_INTERPROCESS_DETAIL_SPIN_MUTEX_HPP
#define BOOST_INTERPROCESS_DETAIL_SPIN_MUTEX_HPP
#if (defined _MSC_VER) && (_MSC_VER >= 1200)
# pragma once
#endif
#include <boost/interprocess/detail/config_begin.hpp>
#include <boost/interprocess/detail/workaround.hpp>
#include <boost/interprocess/detail/posix_time_types_wrk.hpp>
#include <boost/assert.hpp>
#include <boost/interprocess/detail/atomic.hpp>
#include <boost/cstdint.hpp>
#include <boost/interprocess/detail/os_thread_functions.hpp>
#include <boost/interprocess/sync/spin/wait.hpp>
namespace boost {
namespace interprocess {
namespace ipcdetail {
class spin_mutex
{
spin_mutex(const spin_mutex &);
spin_mutex &operator=(const spin_mutex &);
public:
spin_mutex();
~spin_mutex();
void lock();
bool try_lock();
bool timed_lock(const boost::posix_time::ptime &abs_time);
void unlock();
void take_ownership(){};
private:
volatile boost::uint32_t m_s;
};
inline spin_mutex::spin_mutex()
: m_s(0)
{
//Note that this class is initialized to zero.
//So zeroed memory can be interpreted as an
//initialized mutex
}
inline spin_mutex::~spin_mutex()
{
//Trivial destructor
}
inline void spin_mutex::lock(void)
{
spin_wait swait;
do{
boost::uint32_t prev_s = ipcdetail::atomic_cas32(const_cast<boost::uint32_t*>(&m_s), 1, 0);
if (m_s == 1 && prev_s == 0){
break;
}
// relinquish current timeslice
swait.yield();
}while (true);
}
inline bool spin_mutex::try_lock(void)
{
boost::uint32_t prev_s = ipcdetail::atomic_cas32(const_cast<boost::uint32_t*>(&m_s), 1, 0);
return m_s == 1 && prev_s == 0;
}
inline bool spin_mutex::timed_lock(const boost::posix_time::ptime &abs_time)
{
if(abs_time == boost::posix_time::pos_infin){
this->lock();
return true;
}
//Obtain current count and target time
boost::posix_time::ptime now = microsec_clock::universal_time();
spin_wait swait;
do{
if(this->try_lock()){
break;
}
now = microsec_clock::universal_time();
if(now >= abs_time){
return false;
}
// relinquish current time slice
swait.yield();
}while (true);
return true;
}
inline void spin_mutex::unlock(void)
{ ipcdetail::atomic_cas32(const_cast<boost::uint32_t*>(&m_s), 0, 1); }
} //namespace ipcdetail {
} //namespace interprocess {
} //namespace boost {
#include <boost/interprocess/detail/config_end.hpp>
#endif //BOOST_INTERPROCESS_DETAIL_SPIN_MUTEX_HPP
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