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<section id="mantid-timers">
<h1>Mantid Timers<a class="headerlink" href="#mantid-timers" title="Link to this heading">#</a></h1>
<p>This page provides an introduction to measuring execution time of the Mantid C++ code.</p>
<section id="wall-clock-timers">
<h2>Wall-clock timers<a class="headerlink" href="#wall-clock-timers" title="Link to this heading">#</a></h2>
<p>Wall-clock time is the <cite>total</cite> time elapsed during execution of code instructions. Mantid wall-clock timer classes
are based on the <a class="reference external" href="https://en.cppreference.com/w/cpp/chrono/high_resolution_clock">std::chrono::high_resolution_clock</a> class.</p>
<section id="class-timer">
<span id="timer"></span><h3>Class Timer<a class="headerlink" href="#class-timer" title="Link to this heading">#</a></h3>
<p><a class="reference external" href="https://github.com/mantidproject/mantid/blob/main/Framework/Kernel/inc/MantidKernel/Timer.h">MantidKernel/Timer</a>
works like a stop-watch. You need to instantiate it before the code being profiled begins and then output its elapsed time right
after the code ends. You can also reset the timer between time measurements, if necessary. An example is given below.</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="n">Mantid</span><span class="o">::</span><span class="n">Kernel</span><span class="o">::</span><span class="n">Timer</span><span class="w"> </span><span class="n">timer</span><span class="p">;</span>
<span class="c1">// do something that takes 5 sec</span>
<span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"did step 1 in "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">timer</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"</span><span class="se">\n</span><span class="s">"</span><span class="p">;</span>
<span class="c1">// do something else that takes 55 sec - the timer still accumulates</span>
<span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"did step 2 after "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">timer</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">" from start</span><span class="se">\n</span><span class="s">"</span><span class="p">;</span>
<span class="n">timer</span><span class="p">.</span><span class="n">reset</span><span class="p">();</span><span class="w"> </span><span class="c1">// reset the timer to zero</span>
<span class="c1">// do something else that takes 5 sec</span>
<span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"step 3 took "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">timer</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"</span><span class="se">\n</span><span class="s">"</span><span class="p">;</span>
<span class="nl">Output</span><span class="p">:</span>
<span class="n">did</span><span class="w"> </span><span class="n">step</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="n">in</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="n">sec</span>
<span class="n">did</span><span class="w"> </span><span class="n">step</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="n">after</span><span class="w"> </span><span class="mi">60</span><span class="w"> </span><span class="n">sec</span>
<span class="n">step</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="n">took</span><span class="w"> </span><span class="mi">5</span><span class="w"> </span><span class="n">sec</span>
</pre></div>
</div>
</section>
<section id="class-codeblocktimer">
<span id="codeblocktimer"></span><h3>Class CodeBlockTimer<a class="headerlink" href="#class-codeblocktimer" title="Link to this heading">#</a></h3>
<p><a class="reference external" href="https://github.com/mantidproject/mantid/blob/main/Framework/Kernel/inc/MantidKernel/Timer.h">MantidKernel/CodeBlockTimer</a> is
designed for timing a block of C++ code inside curly braces, i.e. inside a scope. You just need to instantiate
a timer object on the stack at the start of the scope and provide an output stream. When the timer goes out of scope,
it automatically outputs the elapsed time to the stream. An example is given below.</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="cp">#include</span><span class="w"> </span><span class="cpf">"Timer.h"</span>
<span class="kt">void</span><span class="w"> </span><span class="nf">MyAlgorithm::doSomething</span><span class="p">()</span>
<span class="p">{</span>
<span class="w"> </span><span class="c1">// Instantiate a timer object on the stack. Specify the name and output stream.</span>
<span class="w"> </span><span class="n">Mantid</span><span class="o">::</span><span class="n">Kernel</span><span class="o">::</span><span class="n">CodeBlockTimer</span><span class="w"> </span><span class="n">timer</span><span class="p">(</span><span class="s">"MyAlgorithm::doSomething"</span><span class="p">,</span><span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="p">);</span>
<span class="w"> </span><span class="c1">// Do something that takes 5 sec</span>
<span class="w"> </span><span class="c1">// ...</span>
<span class="w"> </span><span class="c1">//</span>
<span class="w"> </span><span class="c1">// When the timer goes out of scope, it will output the results</span>
<span class="p">}</span>
<span class="nl">Output</span><span class="p">:</span><span class="w"> </span><span class="n">Elapsed</span><span class="w"> </span><span class="n">time</span><span class="w"> </span><span class="p">(</span><span class="n">sec</span><span class="p">)</span><span class="w"> </span><span class="n">in</span><span class="w"> </span><span class="s">"MyAlgorithm::doSomething"</span><span class="o">:</span><span class="w"> </span><span class="mi">5</span>
</pre></div>
</div>
<p>The above example shows how to time a whole function. You can, however, break a function into smaller blocks of code using curly
braces and time each code block separately. Note, when a code block is executed multiple times, <cite>CodeBlockTimer</cite> will output the elapsed
time for each execution. If you don’t want to have multiple lines of output and are interested in the total elapsed time, use <a class="reference internal" href="#codeblockmultipletimer"><span class="std std-ref">CodeBlockMultipleTimer</span></a>.</p>
</section>
<section id="class-codeblockmultipletimer">
<span id="codeblockmultipletimer"></span><h3>Class CodeBlockMultipleTimer<a class="headerlink" href="#class-codeblockmultipletimer" title="Link to this heading">#</a></h3>
<p><a class="reference external" href="https://github.com/mantidproject/mantid/blob/main/Framework/Kernel/inc/MantidKernel/Timer.h">MantidKernel/CodeBlockMultipleTimer</a> is designed
for timing a block of code that is called multiple times. Similar to <a class="reference internal" href="#codeblocktimer"><span class="std std-ref">CodeBlockTimer</span></a>, it needs to be instantiated on the stack at the
start of the scope. The constructor takes in a <a class="reference external" href="https://github.com/mantidproject/mantid/blob/main/Framework/Kernel/inc/MantidKernel/Timer.h">MantidKernel/CodeBlockMultipleTimer::TimeAccumulator</a>
object. Unlike the timer, which gets destroyed at the end of the scope, the time accumulator has to be persistent. One possibility is to declare it
with a static linkage in the same compilation unit and provide an accessor function. Every time the timer goes out of scope, it automatically updates the time accumulator.
The time accumulator can later be accessed to report the total elapsed time. In the example below Algorithm B calls a method on Algorithm A several times and outputs the total time elapsed in that method.</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="c1">// File MyAlgorithm_A.cpp</span>
<span class="cp">#include</span><span class="w"> </span><span class="cpf">"Timer.h"</span>
<span class="c1">// Declare a time accumulator with a static linkage</span>
<span class="k">static</span><span class="w"> </span><span class="n">Mantid</span><span class="o">::</span><span class="n">Kernel</span><span class="o">::</span><span class="n">CodeBlockMultipleTimer</span><span class="o">::</span><span class="n">TimeAccumulator</span><span class="w"> </span><span class="n">s_timeAccumulator</span><span class="p">(</span><span class="s">"MyAlgorithm_A::doSomething"</span><span class="p">);</span>
<span class="c1">// Provide an accessor function</span>
<span class="n">MANTID_KERNEL_DLL</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">Mantid</span><span class="o">::</span><span class="n">Kernel</span><span class="o">::</span><span class="n">CodeBlockMultipleTimer</span><span class="o">::</span><span class="n">TimeAccumulator</span><span class="o">&</span><span class="w"> </span><span class="n">myAlgorithm_A_TimeAccumulator</span><span class="p">(){</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">s_timeAccumulator</span><span class="p">;</span>
<span class="p">}</span>
<span class="c1">// ...</span>
<span class="kt">void</span><span class="w"> </span><span class="n">MyAlgorithm_A</span><span class="o">::</span><span class="n">doSomething</span><span class="p">(){</span>
<span class="w"> </span><span class="c1">// Declare a timer object on the stack. Specify the time accumulator.</span>
<span class="w"> </span><span class="n">Mantid</span><span class="o">::</span><span class="n">Kernel</span><span class="o">::</span><span class="n">CodeBlockMultipleTimer</span><span class="w"> </span><span class="nf">timer</span><span class="p">(</span><span class="n">s_timeAccumulator</span><span class="p">);</span>
<span class="w"> </span><span class="c1">// Do something that takes 5 sec</span>
<span class="w"> </span><span class="c1">// ...</span>
<span class="w"> </span><span class="c1">//</span>
<span class="w"> </span><span class="c1">// When the timer goes out of scope, it will update the time accumulator</span>
<span class="p">}</span>
<span class="c1">// File MyAlgorithm_B.cpp</span>
<span class="cp">#include</span><span class="w"> </span><span class="cpf">"Timer.h"</span>
<span class="c1">// Let the linker know that the accessor function for the time accumulator is defined in another compilation unit</span>
<span class="k">extern</span><span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="n">Mantid</span><span class="o">::</span><span class="n">Kernel</span><span class="o">::</span><span class="n">CodeBlockMultipleTimer</span><span class="o">::</span><span class="n">TimeAccumulator</span><span class="o">&</span><span class="w"> </span><span class="n">myAlgorithm_A_TimeAccumulator</span><span class="p">();</span>
<span class="kt">void</span><span class="w"> </span><span class="nf">MyAlgorithm_B::doSomething</span><span class="p">(){</span>
<span class="w"> </span><span class="c1">// Call MyAlgorithm_A::doSomething() 3 times</span>
<span class="w"> </span><span class="c1">// ...</span>
<span class="w"> </span><span class="c1">//</span>
<span class="w"> </span><span class="c1">// Output the results</span>
<span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">myAlgorithm_A_TimeAccumulator</span><span class="p">()</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="sc">'\n'</span><span class="p">;</span>
<span class="p">}</span>
<span class="nl">Output</span><span class="p">:</span><span class="w"> </span><span class="n">Elapsed</span><span class="w"> </span><span class="n">time</span><span class="w"> </span><span class="p">(</span><span class="n">sec</span><span class="p">)</span><span class="w"> </span><span class="n">in</span><span class="w"> </span><span class="s">"MyAlgorithm_A::doSomething"</span><span class="o">:</span><span class="w"> </span><span class="mi">15</span><span class="p">;</span><span class="w"> </span><span class="n">Number</span><span class="w"> </span><span class="n">of</span><span class="w"> </span><span class="n">entrances</span><span class="o">:</span><span class="w"> </span><span class="mi">3</span>
</pre></div>
</div>
</section>
</section>
<section id="cpu-timers">
<h2>CPU timers<a class="headerlink" href="#cpu-timers" title="Link to this heading">#</a></h2>
<p>CPU time is the time spent by the CPU while processing code instructions. Unlike wall-clock time, CPU time does not include
time spent waiting for disk, network or other resources, e.g. I/O operations.</p>
<section id="class-cputimer">
<h3>Class CPUTimer<a class="headerlink" href="#class-cputimer" title="Link to this heading">#</a></h3>
<p><a class="reference external" href="https://github.com/mantidproject/mantid/blob/main/Framework/Kernel/inc/MantidKernel/CPUTimer.h">MantidKernel/CPUTimer</a>
measures both CPU time and wall-clock time. The CPU time measurement utilizes
<a class="reference external" href="https://en.cppreference.com/w/cpp/chrono/c/clock">std::clock()</a> function. The wall-clock time measurement uses <a class="reference internal" href="#timer"><span class="std std-ref">Timer</span></a> class.
The output includes the wall-clock time and the ratio of the CPU time to the wall-clock time. Note, since CPU time and wall-clock time are measured
with different accuracy, it is possible to have a ratio greater than 1.
A code example is given below.</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="n">Mantid</span><span class="o">::</span><span class="n">Kernel</span><span class="o">::</span><span class="n">CPUTimer</span><span class="w"> </span><span class="n">timer</span><span class="p">;</span>
<span class="c1">// do something that takes 5 sec</span>
<span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"did step 1 in "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">timer</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"</span><span class="se">\n</span><span class="s">"</span><span class="p">;</span>
<span class="c1">// do something else that takes 55 sec - the timer still accumulates</span>
<span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"did step 2 after "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">timer</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">" from start</span><span class="se">\n</span><span class="s">"</span><span class="p">;</span>
<span class="n">timer</span><span class="p">.</span><span class="n">reset</span><span class="p">();</span><span class="w"> </span><span class="c1">// reset the timer to zero</span>
<span class="c1">// do something else that takes 5 sec</span>
<span class="n">std</span><span class="o">::</span><span class="n">cout</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"step 3 took "</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="n">timer</span><span class="w"> </span><span class="o"><<</span><span class="w"> </span><span class="s">"</span><span class="se">\n</span><span class="s">"</span><span class="p">;</span>
<span class="nl">Output</span><span class="p">:</span>
<span class="n">did</span><span class="w"> </span><span class="n">step</span><span class="w"> </span><span class="mi">1</span><span class="w"> </span><span class="n">in</span><span class="w"> </span><span class="mf">5.0000</span><span class="w"> </span><span class="n">sec</span><span class="p">,</span><span class="w"> </span><span class="n">CPU</span><span class="w"> </span><span class="n">Fraction</span><span class="w"> </span><span class="mf">1.00</span>
<span class="n">did</span><span class="w"> </span><span class="n">step</span><span class="w"> </span><span class="mi">2</span><span class="w"> </span><span class="n">after</span><span class="w"> </span><span class="mf">60.0000</span><span class="w"> </span><span class="n">sec</span><span class="p">,</span><span class="w"> </span><span class="n">CPU</span><span class="w"> </span><span class="n">Fraction</span><span class="w"> </span><span class="mf">0.99</span>
<span class="n">step</span><span class="w"> </span><span class="mi">3</span><span class="w"> </span><span class="n">took</span><span class="w"> </span><span class="mf">5.0000</span><span class="w"> </span><span class="n">sec</span><span class="p">,</span><span class="w"> </span><span class="n">CPU</span><span class="w"> </span><span class="n">Fraction</span><span class="w"> </span><span class="mf">1.00</span>
</pre></div>
</div>
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