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POWhat's wrong with this threads pool / multi-core simulation
 

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  1. POWhat's wrong with this threads pool / multi-core simulation
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    <p>Hy everyone. I've been trying to make a kind of threads pool, meant to simulate a multi-core processor, where I have a number of threads running all the time( the core ), that I later dispatch to process a ( fixed for now) function. The idea to have the threads running at all time is that I don't have the thread creation/destruction overhead. There are three problems with what I'm doing now. First, the results are all wrong. Second, the function measuring the time is reporting 0 ms Third, the program calls abort at exit. Here's the code I'm using:</p> <pre><code> auto fakeExpensiveOperation = [](int i) -&gt; float { Sleep(10); return sqrt(i); }; // Performance test int size = 4000; float* out = new float[size]; #define THREAD_RUNNING 0 #define THREAD_FINISHED (1 &lt;&lt; 0) #define THREAD_EXIT (1 &lt;&lt; 1) #define THREAD_STALL (1 &lt;&lt; 2) const int coreCount = 8; thread cores[coreCount]; atomic&lt;unsigned int&gt; msgArray[coreCount]; for (auto&amp; msg : msgArray) msg.store(THREAD_STALL); auto kernel = [out, &amp;fakeExpensiveOperation](int idx){ out[idx] = fakeExpensiveOperation(idx); }; for (int i = 0; i &lt; coreCount; i++) { cores[i] = thread([&amp;msgArray, i, kernel]() { while (true) { unsigned int msg = msgArray[i].load(); if((msg &amp; THREAD_STALL) == THREAD_STALL) continue; if ((msg &amp; THREAD_EXIT) == THREAD_EXIT) break; if ((msg &amp; THREAD_RUNNING) == THREAD_RUNNING) { int idx = (msg &gt;&gt; 3) + i; // Do the function kernel(idx); msgArray[i].store(THREAD_FINISHED); } } }); } auto t2 = time_call([&amp;]() { for (int i = 0; i &lt; size; i += coreCount) { for (int n = 0; n &lt; coreCount; n++) { if((msgArray[n].load() &amp; THREAD_RUNNING) == THREAD_RUNNING) continue; // The core is still working unsigned int msg = THREAD_RUNNING; msg |= (i &lt;&lt; 3); msgArray[n].store(msg); } } }); for (int n = 0; n &lt; coreCount; n++) msgArray[n].store(THREAD_EXIT); cout &lt;&lt; "sqrt 0 : " &lt;&lt; out[0] &lt;&lt; endl; cout &lt;&lt; "sqrt 1 : " &lt;&lt; out[1] &lt;&lt; endl; cout &lt;&lt; "sqrt 2 : " &lt;&lt; out[2] &lt;&lt; endl; cout &lt;&lt; "sqrt 4 : " &lt;&lt; out[4] &lt;&lt; endl; cout &lt;&lt; "sqrt 16 : " &lt;&lt; out[16] &lt;&lt; endl; cout &lt;&lt; "Parallel : " &lt;&lt; t2 &lt;&lt; endl; system("pause"); delete[] out; return 0; </code></pre> <p>I'm really out of ideas. Can anyone point out what's wrong here?</p> <p>EDIT: I did the changes i mentioned, and still get wrong values. I changed the values of the flags, and detached the threads after creating them.</p>
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    1. PTQuestion
    1. USSantiago Pacheco
    1. USSantiago Pacheco
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      1. POWhat's wrong with this threads pool / multi-core simulation
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      1. VTUpMod
    1. COSince `THREAD_RUNNING` is 0, `(foo & THREAD_RUNNING) == THREAD_RUNNING` is a complicated way to write `true`.
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      1. POWhat's wrong with this threads pool / multi-core simulation
      1. USCasey
    2. COYou never `join` or `detach` your threads, so `std::terminate` is called when their destructors run.
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      1. POWhat's wrong with this threads pool / multi-core simulation
      1. USCasey
    3. COYou are both right! :facepalm. I should detach the threads, and change the value in THREAD_RUNNING. I can't try it now, but i'll try it later.
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      1. POWhat's wrong with this threads pool / multi-core simulation
      1. USSantiago Pacheco
 

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