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POC++ Intel TBB and Microsoft PPL, how to use next_permutation in a parallel loop?
 

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    <p>I have Visual Studio 2012 with Intel parallel studio 2013 installed, so I have Intel TBB.</p> <p>Say I have the following piece of code:</p> <pre><code>const int cardsCount = 12; // will be READ by all threads // the required number of cards of each colour to complete its set: // NOTE that the required number of cards of each colour is not the same as the total number of cards of this colour available int required[] = {2,3,4}; // will be READ by all threads Card cards[cardsCount]; // will be READ by all threads int cardsIndices[cardsCount];// this will be permuted, permutations need to be split among threads ! // set "cards" to 4 cards of each colour (3 colours total = 12 cards) // set cardsIndices to {0,1,2,3...,11} // this variable will be written to by all threads, maybe have one for each thread and combine them later?? or can I use concurrent_vector&lt;int&gt; instead !? int logColours[] = {0,0,0}; int permutationsCount = fact(cardsCount); for (int pNum=0; pNum&lt;permutationsCount; pNum++) // I want to make this loop parallel !! { int countColours[3] = {0,0,0}; // local loop variable, no problem with multithreading for (int i=0; i&lt;cardsCount; i++) { Card c = cards[cardsIndices[i]]; // accessed "cards" countColours[c.Colour]++; // local loop variable, np. // we got the required number of cards of this colour to complete it if (countColours[c.Colour] == required[c.Colour]) // read global variable "required" ! { // log that we completed this colour and go to next permutation logColours[c.Colour] ++; // should I use a concurrent_vector&lt;int&gt; for this shared variable? break; } } std::next_permutation(cardsIndices, cardsIndices+cardsCount); // !! this is my main issue } </code></pre> <p>What I'm calculating is how many times we will complete a colour if we pick randomly from available cards, and that's done exhaustively by going through each permutation possible and picking sequentially, when a colour is "complete" we break and go to the next permutation. Note that we have 4 cards of each colour but the required number of cards to complete each colour is {2,3,4} for Red, Green, Blue. 2 red cards are enough to complete red and we have 4 available, hence red is more likely to be completed than blue which requires all 4 cards to be picked.</p> <p>I want to make this for-loop parallel, but my main problem is how to deal with "cards" permutations? you have ~0.5 billion permutation here (12!), if I have 4 threads how can I split this into 4 different quarters and let every thread go through each of them?</p> <p>What if I don't know the number of cores the machine has and I want the program to automatically choose the right number of concurrent threads? surely there must be a way to do that using Intel or Microsoft tools?</p> <p>This is my Card struct just in case:</p> <pre><code>struct Card { public: int Colour; int Symbol; } </code></pre>
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