cpp
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EAStdC
zrcadlo https://github.com/electronicarts/EAStdC.git


			
				
					
						
						
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<h1>EAStopwatch</h1>

<h2>Introduction</h2>
<p>EAStopwatch provides timing facilities for use in game development. It provides 
  two C++ classes:</p>
<blockquote>
  <table width="100%" border="1">
    <tr>
      <td>Stopwatch</td>
      <td>A general-purpose timer</td>
    </tr>
    <tr>
      <td>LimitStopwatch</td>
      <td>A special-purpose countdown-style timer</td>
    </tr>
  </table>
</blockquote>
<p>Stopwatch acts much like and classic hand-held stopwatch or like the stopwatch 
  found on sports watches. It has additional flexibility, such as the ability 
  to set an elapsed time to any value.</p>
<p>LimitStopwatch is a stopwatch which simply tells you if a given amount of time 
  has passed. You can accomplish this same functionality by polling a Stopwatch, 
  but LimitStopwatch is more efficient.</p>
<h2>Important things to remember</h2>
<ul>
  <li> You won't get very accurate timings if you use a millisecond stopwatch 
    repeatedly to time tiny sections of code that take only nanoseconds.</li>
  <li>You can start and stop a stopwatch repeatedly and it will do the right thing, 
    which is sum up the times during which it was running.</li>
  <li>Timing CPU cycles (clock ticks) accurately can be hard if you are trying 
    to time very small pieces of code. Pipeline stalls and memory stalls can result 
    in highly variable results.</li>
  <li>A running stopwatch consumes no resources (CPU cycles nor memory) during 
    its existence nor while it is running.</li>
  <li>You don't have to stop a stopwatch that is running; it doesn't take up CPU 
    time to be running. It is not an error to not stop a stopwatch.</li>
  <li>There is a distinction between stopwatch cycles and CPU-based cycles. While 
    it may be the case that the stopwatch uses a CPU cycle counter as its basis, 
    this also may not be the case. In fact, using a CPU cycles counter as the 
    basis for a stopwatch is often a dangerous thing to do because processors 
    these days will sometimes switch frequencies on the fly. </li>
  <li>You don't have to worry about multi-processor issues unless you are running 
    on a desktop platform such as Windows. In the case of such platforms, you 
    only need to worry about such issues if you happen to define EA_STOPWATCH_FORCE_CPU_CYCLE_USAGE = 1.</li>
  <li>You can call safely GetElapsedTime while the stopwatch is running; it will 
    simply return the currently elapsed time.</li>
  <li>The construction and destruction instances of Stopwatch is fast; don't worry 
    about it. Similarly, a Stopwatch instance is small in size.</li>
</ul>
<h2>Example usage </h2>
<p>EAStopwatch is very easy to use, though curiously its simplicity actually confuses 
  some users familiar with more cumbersome alternatives.</p>
<p>Basic usage:</p>
<pre class="code-example">Stopwatch stopwatch(Stopwatch::kUnitsMilliseconds);

stopwatch.Start();
DoSomethingThatYouWantToMeasure();
printf("Time to do something: %u.\n", stopwatch.GetElapsedTime());</pre>
Example of stopwatch reuse (via Restart):
<pre class="code-example">Stopwatch stopwatch(Stopwatch::kUnitsCycles, true); // Note that 'true' tells the timer to auto-start here.

DoSomethingSmall();
printf("Time to do something small: %u.\n", stopwatch.GetElapsedTime());

stopwatch.Restart();
DoSomethingElseSmall();
printf("Time to do something else small: %d.\n", stopwatch.GetElapsedTime());</pre>
Example of SetElapsedTime usage.
<pre class="code-example">Stopwatch stopwatch(Stopwatch::kUnitsMilliseconds);

stopwatch.SetElapsedTime(100); // Give the stopwatch a &quot;100 ms head start.&quot;
stopwatch.Start();
printf("This should print out 100 (or maybe 101): %u.\n", stopwatch.GetElapsedTime());</pre>
<p>Example of LimitStopwatch usage:</p>
<pre class="code-example">LimitStopwatch limitStopwatch(Stopwatch::kUnitsMilliseconds, 1000, true);

while(!limitStopwatch.IsTimeUp())
    printf("waiting\n"); </pre>
<h2>Don't do this!</h2>
<p> It seems that quite often people unfamiliar with a C++ stopwatch tend to revert 
  away from using the stopwatch as it was designed and try to do timings manually, 
  like shown below. The code below is more complicated than it needs to be and 
  is less precise than it can be, as the high internal resolution of the stopwatch 
  is lost when using it like this. </p>
<pre class="code-example"><font color="#CC0000">Stopwatch stopwatch(Stopwatch::kUnitsMilliseconds);

stopwatch.Start();
uint64_t timeStart = stopwatch.GetElapsedTime();
DoSomething();
uint64_t timeElapsed = stopwatch.GetElapsedTime() - time;</font>
</pre>
<h2>Interface </h2>
<p>Stopwatch</p>
<pre class="code-example">class Stopwatch
{
public:
<span class="code-example-comment">    /// Units
    /// Defines common timing units plus a user-definable set of units.
</span>    enum Units
    {
        kUnitsCycles       =    0,  <font color="#999999">/// Stopwatch clock ticks. </font>
        kUnitsCPUCycles    =    1,  <font color="#999999">/// CPU clock ticks (or similar equivalent for the platform).</font>
        kUnitsNanoseconds  =    2,  <font color="#999999">/// Count in nanoseconds.</font>
        kUnitsMicroseconds =    3,  <font color="#999999">/// Count in microseconds.</font>
        kUnitsMilliseconds =    4,  <font color="#999999">/// Count in milliseconds.</font>
        kUnitsSeconds      =    5,  <font color="#999999">/// Count in seconds.</font>
        kUnitsMinutes      =    6,  <font color="#999999">/// Count in minutes.</font>
        kUnitsUserDefined  = 1000   <font color="#999999">/// User defined units (animation frames, video vertical retrace, etc.).</font>
    };

public:
<span class="code-example-comment">    /// Stopwatch
    /// Constructor for Stopwatch, allows user to specify units. 
    /// If units are kUnitsUserDefined,  you'll need to either subclass 
    /// Stopwatch and implement GetUserDefinedStopwatchCycle or call 
    /// SetUserDefinedUnitsToStopwatchCyclesRatio in order to allow it 
    /// to know how to convert units.
</span>    explicit Stopwatch(int nUnits = kUnitsCycles, bool bStartImmediately = false);

<span class="code-example-comment">    /// Stopwatch
    /// Copy constructor.
</span>    Stopwatch(const Stopwatch& stopwatch);

<span class="code-example-comment">    /// ~Stopwatch
    /// Destructor.
</span>    ~Stopwatch();

<span class="code-example-comment">    /// operator=
    /// Assignment operator.
</span>    Stopwatch& operator=(const Stopwatch& stopwatch);

<span class="code-example-comment">    /// GetUnits
    /// Gets the current units. Returns one of enum Units or kUnitsUserDefined+.
</span>    int GetUnits() const;

<span class="code-example-comment">    /// SetUnits
    /// Sets the current units. One of enum Units or kUnitsUserDefined+.
</span>    void SetUnits(int nUnits);

<span class="code-example-comment">    /// Start
    /// Starts the stopwatch. Continues where it was last stopped. 
    /// Does nothing if the stopwatch is already started.
</span>    void Start();

<span class="code-example-comment">    /// Stop
    /// Stops the stopwatch it it was running and retaines the elasped time.
</span>    void Stop();

<span class="code-example-comment">    /// Reset
    /// Stops the stopwatch if it was running and clears the elapsed time.
</span>    void Reset();

<span class="code-example-comment">    /// Restart
    /// Clears the elapsed time and starts the stopwatch if it was not 
    /// already running. Has the same effect as Reset(), Start().
</span>    void Restart();

<span class="code-example-comment">    /// IsRunning
    /// Returns true if the stopwatch is running.
</span>    bool IsRunning() const;

<span class="code-example-comment">    /// GetElapsedTime
    /// Gets the elapsed time, which properly takes into account any 
    /// intervening stops and starts. Works properly whether the stopwatch 
    /// is running or not.
</span>    uint64_t GetElapsedTime() const;

<span class="code-example-comment">    /// SetElapsedTime
    /// Allows you to set the elapsed time. Erases whatever is current. 
    /// Works properly whether the stopwatch is running or not.
</span>    void SetElapsedTime(uint64_t nElapsedTime);

<span class="code-example-comment">    /// GetElapsedTimeFloat
    /// Float version, which is useful for counting fractions of 
    /// seconds or possibly milliseconds.
</span>    float GetElapsedTimeFloat() const;

<span class="code-example-comment">    /// SetElapsedTimeFloat
    /// Allows you to set the elapsed time. Erases whatever is current. 
    /// Works properly whether the stopwatch is running or not.
</span>    void SetElapsedTimeFloat(float fElapsedTime);

<span class="code-example-comment">    /// SetCyclesPerUnit
    /// Allows the user to manually override the frequency of the 
    /// timer. 
</span>    void SetCyclesPerUnit(float fCyclesPerUnit);

<span class="code-example-comment">    /// GetCyclesPerUnit
    /// Returns the value number of cycles per unit. If the user 
    /// set a manual value via SetCyclesPerUnit, this function returns 
    /// that value.
</span>    float GetCyclesPerUnit() const;

<span class="code-example-comment">    /// GetStopwatchCycle
    /// Gets the current stopwatch cycle on the current machine.
    /// Note that a stopwatch cyle may or may not be the same thing
    /// as a CPU cycle. We provide the distinction between stopwatch
    /// cycles and CPU cycles in order to accomodate platforms (e.g.
    /// desktop platforms) in which CPU cycle counting is unreliable.
</span>    static uint64_t GetStopwatchCycle();

<span class="code-example-comment">    /// GetStopwatchFrequency
    /// Note that the stopwatch freqency may or may not be the same thing
    /// as the CPU freqency. We provide the distinction between stopwatch
    /// cycles and CPU cycles in order to accomodate platforms (e.g.
    /// desktop platforms) in which CPU cycle counting is unreliable.
</span>    static uint64_t GetStopwatchFrequency();

<span class="code-example-comment">    /// GetUnitsPerStopwatchCycle
    /// Returns the number of stopwatch cycles per the given unit.  
    /// If the unit is seconds, the return value would be the frequency of 
    /// the stopwatch timer and thus be the same value as returned by
    /// GetStopwatchFrequency().
</span>    static float GetUnitsPerStopwatchCycle(Units units);

<span class="code-example-comment">    /// GetCPUCycle
    /// Gets the current CPU-based timer cycle on the current processor 
    /// (if in a multiprocessor system). Note that this doesn't necessarily
    /// get the actual machine CPU clock cycle; rather it returns the 
    /// CPU-based timer cycle. One some platforms the CPU-based timer is
    /// a 1:1 relation to the CPU clock, while on others it is some multiple
    /// of it.
</span>    static uint64_t GetCPUCycle();

<span class="code-example-comment">    /// GetCPUFrequency
    /// Gets the frequency of the CPU-based timer. Note that this doesn't 
    /// necessarily get the actual machine CPU clock frequency; rather it returns  
    /// the CPU-based timer frequency. One some platforms the CPU-based timer is
    /// a 1:1 relation to the CPU clock, while on others it is some multiple of it.
</span>    static uint64_t GetCPUFrequency(); 

<span class="code-example-comment">    /// GetUnitsPerCPUCycle
    /// Returns the number of CPU cycles per the given unit.  
    /// If the unit is seconds, the return value would be the frequency 
    /// of the CPU-based timer.
</span>    static float GetUnitsPerCPUCycle(Units units);
};
  </pre>
<p>LimitStopwatch</p>
<pre class="code-example">class LimitStopwatch : public Stopwatch
{
public:
<span class="code-example-comment">    /// LimitStopwatch
    /// Constructor
</span>    LimitStopwatch(int nUnits = kUnitsCycles, uint32_t nLimit = 0, bool bStartImmediately = false);

<span class="code-example-comment">    /// SetTimeLimit
    /// Sets the time limit and lets you start the stopwatch at the same time.
</span>    void SetTimeLimit(uint32_t nLimit, bool bStartImmediately = false); 

<span class="code-example-comment">    /// IsTimeUp
    /// Returns true if the limit has been reached. Highly efficient.
</span>    bool IsTimeUp();

<span class="code-example-comment">    /// GetTimeRemaining
    /// More expensive than IsTimeUp, as it returns a value.
</span>    int64_t GetTimeRemaining();

<span class="code-example-comment">    /// GetTimeRemainingFloat
    /// More expensive than IsTimeUp, as it returns a value.
</span>    float GetTimeRemainingFloat();
};</pre>
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