#include <boost/utility.hpp>
#include <boost/date_time/posix_time/posix_time.hpp>
#include <boost/scoped_ptr.hpp>
+#include <boost/cstdint.hpp>
#include "../Utils/singleton.hh"
//#include "ClockService.mpp"
namespace detail { class ClockServiceTest; }
#endif
- // Implementation note:
+ // Implementation note: The clock value is represented as a 64bit unsigned integer number of
+ // nanosecods based on the CLOCK_MONOTONIC POSIX clock.
//
- // The clock value is represented as a 64bit unsigned integer number of nanosecods elapsed since
- // the construction of the ClockService object.
- //
- // The implementation must provide two features:
- // a) It must reliably detect clock changes
- // b) In case of a clock change a reasonably accurate fallback clock value must be provided
- //
- // We do this using setitimer/getitimer. We setup an interval timer sending SIGALRM whenever
- // CheckInverval seconds have elapsed.
- //
- // On every SIGALRM signal we save the current value of gettimeofday(). If this new value is
- // substantially different from the currently saved value + CheckInterval, the clock has been
- // changed.
- //
- // Whenever the current clock value is requested using now(), the current gettimeofday() value
- // is compared with the saved value. If the difference is substantially more than CheckInterval,
- // the clock has been changed.
- //
- // This provides clock skew detection. If clock skew is detected, we need to move base_ by the
- // amount the time has been changed. To do this we need an as accurate as possible approximation
- // of the expected current time value. We need to differentiate two cases:
- //
- // a) Clock skew detected within now()
- //
- // In this case, we use getitimer() to find the time remaining in the timer. Using this value
- // and the saved gettimeofday() value we can adjust base_ accordingly.
- //
- // b) Clock skew detected in the signal handler
- //
- // In this case we use the saved gettimeofday() value + CheckInterval to adjust base_.
+ // To allow conversion between clock value and absolute time, the ClockService samples the
+ // absolute current time and the clock value when the conversion is performed. This is done at
+ // most once per second on a if-needed basis.
/** \brief Reliable high precision monotonous clock source
The ClockService provides a highly accurate monotonous clock source based on
gettimeofday(). However, it takes additional precautions to detect clock skew.
- \implementation We use a mix of static and non-static members to achieve high performance
- in the normal case (no clock skew) and still encapsulate the dependency on legacy C
- headers. Using the senf::singleton mixin ensures, that the instance is constructed
- before main even when instance() is not called.
+ \implementation The funny mixture of static and non-static members stems from the old
+ implementation based on interval timers and gettimeofday(). The current implementation
+ usses POSIX clocks and is much simpler and more precise.
*/
class ClockService
: singleton<ClockService>
*/
typedef boost::int_fast64_t clock_type;
+ /** \brief Supplementary integer type
+
+ This type is used to represent varies supplementary values (e.g. number of microseconds)
+ */
+ typedef boost::int_fast64_t int64_type;
+
/** \brief Absolute time data type
Boost.DateTime datatype used to represent absolute date/time values.
*/
typedef boost::posix_time::ptime abstime_type;
- static unsigned const CheckInterval = 10;
-
- ///////////////////////////////////////////////////////////////////////////
- ///\name Structors and default members
- ///@{
-
- ~ClockService();
-
- ///@}
///////////////////////////////////////////////////////////////////////////
static clock_type now(); ///< Return current clock value
/**< This member converts an absolute time value
represented as a timeval value into a clock value */
- static clock_type nanoseconds(clock_type v);
- static clock_type microseconds(clock_type v);
- static clock_type milliseconds(clock_type v);
- static clock_type seconds(clock_type v);
- static clock_type minutes(clock_type v);
- static clock_type hours(clock_type v);
- static clock_type days(clock_type v);
-
- static void restart();
+ static clock_type nanoseconds(int64_type v); ///< Convert \a v nanoseconds to clock_type
+ static clock_type microseconds(int64_type v); ///< Convert \a v microseconds to clock_type
+ static clock_type milliseconds(int64_type v); ///< Convert \a v milliseconds to clock_type
+ static clock_type seconds(int64_type v); ///< Convert \a v seconds to clock_type
+ static clock_type minutes(int64_type v); ///< Convert \a v minutes to clock_type
+ static clock_type hours(int64_type v); ///< Convert \a v hours to clock_type
+ static clock_type days(int64_type v); ///< Convert \a v days to clock_type
+
+ static int64_type in_nanoseconds(clock_type v); ///< Convert \a v to nanoseconds
+ static int64_type in_microseconds(clock_type v); ///< Convert \a v to microseconds
+ static int64_type in_milliseconds(clock_type v); ///< Convert \a v to milliseconds
+ static int64_type in_seconds(clock_type v); ///< Convert \a v to seconds
+ static int64_type in_minutes(clock_type v); ///< Convert \a v to minutes
+ static int64_type in_hours(clock_type v); ///< Convert \a v to hours
+ static int64_type in_days(clock_type v); ///< Convert \a v to days
+
+ static void restart(); ///< Force re-syncronisation of abstime and clock
+ /**< Calling the member should never be necessary since
+ abstime() / clock() automatically call restart() if
+ needed */
private:
ClockService();
- void timer();
-
- clock_type now_m();
abstime_type abstime_m(clock_type clock);
clock_type clock_m(abstime_type time);
- void restart_m(bool restart = true);
-
- bool checkSkew(boost::posix_time::ptime time);
- void updateSkew(boost::posix_time::ptime time);
- void clockSkew(boost::posix_time::ptime time, boost::posix_time::ptime expected);
-
- void restartTimer(bool restart = true);
+ void restart_m();
- boost::posix_time::ptime base_;
- boost::posix_time::ptime heartbeat_;
+ boost::posix_time::ptime baseAbstime_;
+ clock_type baseClock_;
- // I don't want this header to depend on the legacy C headers.
/// Internal: ClockService private data (PIMPL idiom)
- struct Impl;
- boost::scoped_ptr<Impl> impl_;
- friend class Impl;
#ifndef DOXYGEN
- friend class senf::detail::ClockServiceTest;
friend class singleton<ClockService>;
#endif
};
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