Source: ../../libxorp/time_slice.hh

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// -*- c-basic-offset: 4; tab-width: 8; indent-tabs-mode: t -*-

// Copyright (c) 2001-2008 XORP, Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the "Software")
// to deal in the Software without restriction, subject to the conditions
// listed in the XORP LICENSE file. These conditions include: you must
// preserve this copyright notice, and you cannot mention the copyright
// holders in advertising related to the Software without their permission.
// The Software is provided WITHOUT ANY WARRANTY, EXPRESS OR IMPLIED. This
// notice is a summary of the XORP LICENSE file; the license in that file is
// legally binding.

// $XORP: xorp/libxorp/time_slice.hh,v 1.12 2008/07/23 05:10:56 pavlin Exp $


#ifndef __LIBXORP_TIME_SLICE_HH__
#define __LIBXORP_TIME_SLICE_HH__

//
// Time-slice class declaration.
//

#ifdef HAVE_SYS_TIME_H
#include <sys/time.h>
#endif

#include "timer.hh"
#include "timeval.hh"


//
// Constants definitions
//

//
// Structures/classes, typedefs and macros
//

/**
 * @short A class for computing whether some processing is taking too long.
 * 
 * This class can be used to compute whether some processing is taking
 * too long time to complete. It is up to the program that uses
 * TimeSlice to check whether the processing is taking too long,
 * and suspend processing of that task if necessary.
 *
 * Example of usage:
<pre>
    TimeSlice time_slice(100000, 20); // 100ms, test every 20th iteration
    
    for (size_t i = 0; i < 1000000000; i++) {
        if (time_slice.is_expired()) {
            // Stop processing.
            // Schedule a timer after 0 ms to continue processing.
            // If needed, save state to continue from here.
            return;
        }
        // Do something CPU-hungry
    }
    time_slice.reset(); // Prepare it again for later usage if needed
</pre>
 */
class TimeSlice {
public:
    /**
     * Constructor for a given time limit and test frequency.
     * 
     * Create a TimeSlice object that will measure time slices
     * with given frequency of testing.
     * The time slice is measured once in @ref test_iter_frequency
     * times when method is_expired() is called.
     * 
     * @param usec_limit the time slice to measure in microseconds.
     * @param test_iter_frequency the frequency of measuring the time slice.
     */
    TimeSlice(uint32_t usec_limit, size_t test_iter_frequency);
    
    /**
     * Reset the TimeSlice object.
     */
    void reset();
    
    /**
     * Test if the time slice has expired.
     * 
     * If the time slice has expired, automatically prepare this object
     * to start measuring again the time slice.
     * 
     * @return true if the time slice has expired, otherwise false.
     */
    bool is_expired();
    
private:
    TimeVal		_time_slice_limit;	// The time slice to measure
    const size_t	_test_iter_frequency;	// The frequency of measuring
    
    TimeVal		_time_slice_start;	// When the time slice started
    size_t		_remain_iter;		// Remaning iterations to
						// check the time
};

//
// Deferred definitions
//
inline bool
TimeSlice::is_expired()
{
    if (--_remain_iter)
	return (false);		// Don't test the time yet
    
    _remain_iter = _test_iter_frequency;
    
    // Test if the time slice has expired
    TimeVal now;
    TimerList::system_gettimeofday(&now);
    if (now - _time_slice_limit < _time_slice_start)
	return (false);		// The time slice has not expired
    
    // The time slice has expired
    _time_slice_start = now;
    return (true);
}

//
// Global variables
//

//
// Global functions prototypes
//

#endif // __LIBXORP_TIME_SLICE_HH__