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<h1>
<span class="m-breadcrumb"><a href="syclFlowAlgorithms.html">syclFlow Algorithms</a> »</span>
Parallel Iterations
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<h3>Contents</h3>
<ul>
<li><a href="#ForEachSYCLIndexBasedParallelFor">Index-based Parallel Iterations</a></li>
<li><a href="#ForEachSYCLIteratorBasedParallelIterations">Iterator-based Parallel Iterations</a></li>
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<p><a href="classtf_1_1syclFlow.html" class="m-doc">tf::<wbr />syclFlow</a> provides two template methods, <a href="classtf_1_1syclFlow.html#a30c3f7a279d1f88b6052f7ded1ee381a" class="m-doc">tf::<wbr />syclFlow::<wbr />for_each</a> and <a href="classtf_1_1syclFlow.html#a25e8aa7d7efbd05ef11353317174574a" class="m-doc">tf::<wbr />syclFlow::<wbr />for_each_index</a>, for creating tasks to perform parallel iterations over a range of items.</p><section id="ForEachSYCLIndexBasedParallelFor"><h2><a href="#ForEachSYCLIndexBasedParallelFor">Index-based Parallel Iterations</a></h2><p>Index-based parallel-for performs parallel iterations over a range <code>[first, last)</code> with the given <code>step</code> size. These indices must be <em>integral</em> type. The task created by <a href="classtf_1_1syclFlow.html#a25e8aa7d7efbd05ef11353317174574a" class="m-doc">tf::<wbr />syclFlow::<wbr />for_each_index(I first, I last, I step, C&& callable)</a> represents a kernel of parallel execution for the following loop:</p><pre class="m-code"><span class="c1">// positive step: first, first+step, first+2*step, ...</span>
<span class="k">for</span><span class="p">(</span><span class="k">auto</span> <span class="n">i</span><span class="o">=</span><span class="n">first</span><span class="p">;</span> <span class="n">i</span><span class="o"><</span><span class="n">last</span><span class="p">;</span> <span class="n">i</span><span class="o">+=</span><span class="n">step</span><span class="p">)</span> <span class="p">{</span>
<span class="n">callable</span><span class="p">(</span><span class="n">i</span><span class="p">);</span>
<span class="p">}</span>
<span class="c1">// negative step: first, first-step, first-2*step, ...</span>
<span class="k">for</span><span class="p">(</span><span class="k">auto</span> <span class="n">i</span><span class="o">=</span><span class="n">first</span><span class="p">;</span> <span class="n">i</span><span class="o">></span><span class="n">last</span><span class="p">;</span> <span class="n">i</span><span class="o">+=</span><span class="n">step</span><span class="p">)</span> <span class="p">{</span>
<span class="n">callable</span><span class="p">(</span><span class="n">i</span><span class="p">);</span>
<span class="p">}</span></pre><p>Each iteration <code>i</code> is independent of each other and is assigned one kernel thread to run the callable. The following example creates a kernel that assigns each element of <code>gpu_data</code> to 1 over the range [0, 100) with step size 1.</p><pre class="m-code"><span class="n">taskflow</span><span class="p">.</span><span class="n">emplace_on</span><span class="p">([</span><span class="o">&</span><span class="p">](</span><span class="n">tf</span><span class="o">::</span><span class="n">syclFlow</span><span class="o">&</span> <span class="n">sf</span><span class="p">){</span>
<span class="c1">// ... create other gpu tasks</span>
<span class="c1">// assigns each element in gpu_data to 1 over the range [0, 100) with step size 1</span>
<span class="n">sf</span><span class="p">.</span><span class="n">for_each_index</span><span class="p">(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">100</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="p">[</span><span class="n">gpu_data</span><span class="p">]</span> <span class="p">(</span><span class="kt">int</span> <span class="n">idx</span><span class="p">)</span> <span class="p">{</span>
<span class="n">gpu_data</span><span class="p">[</span><span class="n">idx</span><span class="p">]</span> <span class="o">=</span> <span class="mi">1</span><span class="p">;</span>
<span class="p">});</span>
<span class="p">},</span> <span class="n">sycl_queue</span><span class="p">);</span></pre></section><section id="ForEachSYCLIteratorBasedParallelIterations"><h2><a href="#ForEachSYCLIteratorBasedParallelIterations">Iterator-based Parallel Iterations</a></h2><p>Iterator-based parallel-for performs parallel iterations over a range specified by two STL-styled iterators, <code>first</code> and <code>last</code>. The task created by <a href="classtf_1_1syclFlow.html#a30c3f7a279d1f88b6052f7ded1ee381a" class="m-doc">tf::<wbr />syclFlow::<wbr />for_each(I first, I last, C&& callable)</a> represents a parallel execution of the following loop:</p><pre class="m-code"><span class="k">for</span><span class="p">(</span><span class="k">auto</span> <span class="n">i</span><span class="o">=</span><span class="n">first</span><span class="p">;</span> <span class="n">i</span><span class="o"><</span><span class="n">last</span><span class="p">;</span> <span class="n">i</span><span class="o">++</span><span class="p">)</span> <span class="p">{</span>
<span class="n">callable</span><span class="p">(</span><span class="o">*</span><span class="n">i</span><span class="p">);</span>
<span class="p">}</span></pre><p>The two iterators, <code>first</code> and <code>last</code>, are typically two raw pointers to the first element and the next to the last element in the range in GPU memory space. The following example creates a <code>for_each</code> kernel that assigns each element in <code>gpu_data</code> to 1 over the range <code>[gpu_data, gpu_data + 1000)</code>.</p><pre class="m-code"><span class="n">taskflow</span><span class="p">.</span><span class="n">emplace_on</span><span class="p">([</span><span class="o">&</span><span class="p">](</span><span class="n">tf</span><span class="o">::</span><span class="n">syclFlow</span><span class="o">&</span> <span class="n">cf</span><span class="p">){</span>
<span class="c1">// ... create gpu tasks</span>
<span class="c1">// assigns each element to 1 over the range [gpu_data, gpu_data + 1000)</span>
<span class="n">cf</span><span class="p">.</span><span class="n">for_each</span><span class="p">(</span><span class="n">gpu_data</span><span class="p">,</span> <span class="n">gpu_data</span> <span class="o">+</span> <span class="mi">1000</span><span class="p">,</span> <span class="p">[]</span> <span class="p">(</span><span class="kt">int</span><span class="o">&</span> <span class="n">item</span><span class="p">)</span> <span class="p">{</span>
<span class="n">item</span> <span class="o">=</span> <span class="mi">1</span><span class="p">;</span>
<span class="p">});</span>
<span class="p">},</span> <span class="n">sycl_queue</span><span class="p">);</span></pre><p>Each iteration is independent of each other and is assigned one kernel thread to run the callable.</p></section>
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