Sample solution

Content

Controlling concurrent access to a shared resource
Sample solution
Pool pattern
Sample solution
Avoiding the overhead of copying
Sample solution
Condition variables
Sample solution

The wanted RAII class can be formulated quite simply:

struct Guard {
   Guard(std::mutex& mutex) : mutex(mutex) {
      mutex.lock();
   }
   ~Guard() {
      mutex.unlock();
   }
   std::mutex& mutex;
};

This allows to simplify the gen method:

double gen() {
   Guard guard(mutex);
   return uniform(mt);
}

It shouldn't be surprising that a similar class is present in the standard C++ library. It is named std::lock_guard and gets the mutex class as template parameter:

double gen() {
   std::lock_guard<std::mutex> guard(mutex);
   return uniform(mt);
}

session16/random_init9.cpp

#include <cstdlib>
#include <mutex>
#include <random>
#include <thread>
#include <vector>
#include <hpc/aux/slices.hpp>
#include <hpc/matvec/gematrix.hpp>
#include <hpc/matvec/iterators.hpp>
#include <hpc/matvec/print.hpp>
#include <hpc/matvec/views.hpp>

using namespace hpc;
using namespace hpc::aux;
using namespace hpc::matvec;

struct Guard {
   Guard(std::mutex& mutex) : mutex(mutex) {
      mutex.lock();
   }
   ~Guard() {
      mutex.unlock();
   }
   std::mutex& mutex;
};

struct MyRandomGenerator {
      MyRandomGenerator() : mt(std::random_device()()), uniform(-100, 100) {
      }
      double gen() {
	 Guard guard(mutex);
	 return uniform(mt);
      }
   private:
      std::mutex mutex;
      std::mt19937 mt;
      std::uniform_real_distribution<double> uniform;
};

template <
   template<typename> class MatrixA, typename T,
   typename RNG,
   Require< Ge<MatrixA<T>> > = true
>
void randomInit(MatrixA<T>& A, RNG& rng) {
   for (auto [i, j, Aij]: A) {
      Aij = rng.gen();
      (void) i; (void) j; // suppress gcc warning
   }
}

int main() {
   MyRandomGenerator rng;
   GeMatrix<double> A(51, 7);
   std::size_t nof_threads = std::thread::hardware_concurrency();

   std::vector<std::thread> threads(nof_threads);
   UniformSlices<std::size_t> slices(nof_threads, A.numRows());
   for (std::size_t index = 0; index < nof_threads; ++index) {
      auto firstRow = slices.offset(index);
      auto numRows = slices.size(index);
      threads[index] = std::thread([
	       A_ = A.view(firstRow, 0, numRows, A.numCols()),
	       &rng
	    ]() mutable {
	 randomInit(A_, rng);
      });
   }
   for (std::size_t index = 0; index < nof_threads; ++index) {
      threads[index].join();
   }
   print(A, " %7.2f");
}

theon$ g++ -O3 -g -I/home/numerik/pub/hpc/ws19/session16 -std=c++17 -o random_init9 random_init9.cpp
theon$ ./random_init9
   91.61   49.35  -90.07   -1.73   53.38   51.23  -55.87
   -0.09   59.57  -81.86    7.13   36.51   58.61  -67.74
  -11.29   80.32    0.60   12.73  -50.94  -88.11  -49.64
  -74.40  -85.65  -87.28   99.93  -41.68   45.43   49.74
    1.28  -51.36  -11.55   64.68   31.23  -74.61    7.18
  -46.01   42.31   93.78   34.98   43.76   22.83   68.01
   15.64   53.39   97.54   54.98   54.81   71.58   23.38
   61.55   28.99  -72.58  -53.40  -89.27   15.82   41.90
  -52.93  -70.69   78.32   75.77  -88.28   91.46  -96.27
  -88.61  -42.34  -35.55  -95.89   89.33   49.25  -67.93
  -82.86  -28.76  -27.17  -53.83   15.62   99.74  -46.57
    8.27   18.07  -28.92    3.59  -31.47   14.57  -98.96
   86.02   98.89   39.52   -6.06  -50.20  -58.07  -13.97
  -17.76   71.63  -19.30  -68.95   82.82  -86.29   63.66
  -17.76   58.16  -80.17  -13.42   64.68  -51.59   23.38
  -52.21  -46.75  -49.71   78.91  -44.79  -80.76   46.36
  -92.83   61.13  -58.99  -33.27   65.28   87.08   68.47
  -24.19   61.61  -27.15   -3.60   35.18  -79.71  -89.43
   62.61  -89.97  -69.77  -99.14   62.69  -48.52  -61.21
   31.61   94.32  -64.62  -28.07  -20.34   61.83   50.32
  -52.11   14.40   88.35   28.56  -95.18   13.58  -68.65
  -69.76  -62.19   82.55  -92.81   61.73  -20.46  -50.85
   68.77  -96.25  -88.00  -64.44  -36.79  -50.65   15.53
   56.47   54.23   50.77  -82.12   18.20   45.96  -90.23
   -9.72   82.45  -44.85  -24.11  -25.19  -46.66    1.41
  -35.86   21.75   -6.24   16.88   79.84   93.77   84.87
   95.53  -46.68  -67.82   32.06   42.29   12.83  -49.82
   64.28  -71.80  -72.42    3.34   91.94   20.69   18.15
   92.27   71.63  -26.76   25.33   32.26   53.55  -84.39
  -16.34   86.35   -0.82  -57.90   65.03   27.03   -5.67
   76.17  -83.67  -11.47  -50.14  -78.98   78.58   34.71
  -71.27  -96.03  -81.47   94.22  -83.45  -60.27   20.21
   91.05  -97.63  -97.52   34.12  -88.73   19.30   63.53
   22.81  -79.23   75.31  -90.29   63.16  -80.96  -49.36
   56.78  -37.00   87.17  -81.72  -33.55   94.02  -73.09
  -28.15  -57.52   94.93   59.49   88.01   47.83  -10.56
  -28.06  -25.82  -71.54  -98.54   92.45  -48.29  -45.50
   87.59  -49.58  -70.30   12.04   -1.07  -53.97    2.61
   -0.56  -11.38  -79.19  -17.73    9.21  -63.06   -5.57
   61.35   23.97   30.37  -55.31   59.32   50.91   69.87
   37.96  -38.15  -45.62  -43.64   92.27  -55.39  -92.96
  -28.69   -5.35   27.90  -35.15  -77.23   80.53  -97.98
   46.34  -54.31  -86.51   -4.11   93.43    9.56   26.70
   95.83   96.01   22.20  -51.69  -10.89  -40.07   66.97
  -97.26   34.83   -5.84  -94.82    8.61   99.26  -45.07
  -76.22    8.70  -81.21   91.94   75.42   -4.36  -21.83
   40.46   60.53  -29.94  -18.61  -73.06   -8.07  -57.41
   95.79   60.00  -35.98   41.66  -63.55  -20.69  -84.39
   49.94   -4.99   -2.60  -52.29  -86.19   97.84  -54.57
  -50.76  -62.99  -55.42   -2.46   -6.69  -40.35   -1.72
   95.16   36.89   53.87  -93.62  -98.90   66.45   71.40
theon$

heim$ g++-8.3 -O3 -g -I/home/numerik/pub/hpc/ws19/session16 -std=c++17 -o random_init9 random_init9.cpp -lpthread
heim$ ./random_init9
  -18.34  -82.55  -33.01  -91.82   66.29  -63.08  -36.06
   60.73   13.11   -2.10  -34.09   -4.36  -74.55  -80.30
  -33.32   -2.48   11.90  -33.01   -7.33  -24.57   99.71
   46.63  -33.19  -65.95   79.95  -29.89   81.73   62.37
   76.24   27.28   78.01   80.30   87.92   44.97   34.63
  -76.45   57.52   65.14  -74.11   -2.50   52.54   84.06
  -38.95  -39.02   42.31  -56.76  -81.40   97.41    0.84
   46.12    6.22   94.45  -67.77  -27.10   82.78   80.81
   98.37   -3.58  -84.42  -29.65  -57.63   97.68   18.13
  -76.42   35.43   63.01   10.97   -7.49    2.80   74.59
  -52.50  -97.72  -51.81  -84.56  -90.63  -19.22   -3.17
   -0.51  -96.08  -26.47   43.56   55.52   68.07  -95.70
  -73.15  -39.50   31.92   58.23   35.16  -90.31   -3.89
  -92.56   55.30   -8.32   76.54    6.01  -47.66  -66.55
  -39.42  -35.45  -95.60   27.47  -88.16  -62.28   15.94
   51.23  -97.71  -35.82  -59.68   41.87  -77.63  -77.37
   64.45  -26.81   17.83  -73.59  -33.78   49.28   79.87
    6.09   95.95   32.82  -73.90   48.78  -24.46   93.57
   62.83   13.84    7.75  -20.36  -66.36  -96.73   -4.96
   35.73  -16.40   -8.27  -99.96   71.48   43.61   94.94
  -26.80  -49.36  -22.05   86.70  -58.31  -96.69   46.33
  -66.13  -29.12   -4.41  -48.35  -31.12   29.71  -56.23
   98.38  -83.27  -98.40   92.54  -11.90   27.21  -43.16
   40.39    4.28  -39.68   52.15   -6.61  -84.01   46.12
   52.59   77.23  -36.01   41.28  -79.12  -31.73  -84.06
  -13.71   36.79   -8.52  -66.18  -61.66  -17.74   93.29
   50.76   75.52   54.44   62.30  -68.51   55.08   69.97
  -49.00  -36.69    5.47  -53.55  -78.76  -70.43    9.67
   92.41    4.08  -64.79   42.40  -39.92   82.12  -43.63
  -61.94  -32.22  -41.77   66.29   87.96  -29.31  -87.35
  -96.97  -85.34    8.35  -87.20  -95.23  -75.19  -47.67
   16.87   61.29   11.63   47.23  -46.51  -77.34  -53.60
  -12.68    3.36   63.32  -84.97   -2.75    9.93  -93.76
  -93.18  -52.16   67.02  -89.03   49.21  -94.10  -26.17
  -94.30   41.42  -20.97  -94.48   17.21  -11.52   -1.29
  -97.55  -78.15  -62.99   57.94   59.94   49.03   67.11
  -84.20  -66.69   46.46   40.61  -89.71   19.00  -63.19
  -37.32  -99.95   47.60  -39.21   92.25   90.55   -6.31
   15.00  -41.40   -6.42   -8.81   88.93   65.85   93.81
  -11.14   25.88   42.76  -12.74   87.93  -40.70   42.24
   49.68  -97.71  -59.77  -88.69   19.16  -96.66   51.56
    0.91  -82.11  -82.97   45.34  -79.66   -5.38    7.66
  -56.58  -86.66    2.56  -58.20   74.97   61.61  -58.98
  -55.46    5.07  -94.96  -10.94   98.06   66.10   81.53
   52.00   58.65  -28.76   -6.70   18.81   -7.81   65.45
   92.34   24.54   50.66  -44.54   56.26   73.81  -83.69
   28.96  -57.15   34.74    8.03   14.05  -60.61   64.28
   49.39   -2.37  -72.26  -83.43   71.89  -24.07   75.06
  -80.89   86.36  -83.71    3.24  -45.31   10.38   44.90
  -61.75   16.39  -38.73   68.59   63.80   54.45  -53.09
   21.63   52.67  -19.17    4.96  -31.57  -65.25   87.11
heim$