CreateThread

This function creates a new Thread object.

Syntax

• shared_ptr<Thread> CreateThread(shared_ptr<Object> entrypoint(shared_ptr<Object> extra), shared_ptr<Object> extra = NULL, const bool start = true);
• shared_ptr<Thread> CreateThread(function<void()> entrypoint, const bool start = true);

Remarks

You can use threads to execute your own calculations or for integration with third-party libraries. Leadwerks is already extensively multi-threaded. The user API commands should never be called on separate threads. Even if your code appears to run without problems, it will cause crashes when it is run on other computers.

The best approach to multithreading is complete separation of data. The main thread should pass data to the auxillary thread and then retrieve a result, as the simple example below demonstrates. Using a lot of mutexes will make code very complicated and eliminate the performance advantage of multithreading.

Returns

Returns a new thread object.

Example

//-----------------------------------------------------------------------------------------------
// 
// This example calculates prime numbers first on a single thread, and then splits the
// task up across multiple CPU cores. THe time is measured and displayed for each run.
// 
//-----------------------------------------------------------------------------------------------

#include "Leadwerks.h"

using namespace Leadwerks;

void CalcPrimeNumbers(const int start, const int size, std::vector<int>& results)
{
    int i;
    for (int num = start; num <= start + size; num++) {
        int count = 0;
        for (i = 2; i <= num / 2; i++) {
            if (num % i == 0) {
                count++;
                break;
            }
        }
        if (count == 0 && num != 1)
        {
            results.push_back(num);
        }
    }
}

int main(int argc, const char* argv[])
{
    int range = 200000;
    std::vector<int> results;

    Print("Single-threaded test:");
    auto starttime = Millisecs();
    CalcPrimeNumbers(1, range, results);
    auto elapsed = Millisecs() - starttime;
    Print(String(elapsed) + " milliseconds");

    int threadcount = 4;
    Print("Multi-threaded test (" + String(threadcount)+ " threads):");
    std::vector<std::vector<int> > mresults(threadcount);
    vector<shared_ptr<Thread> > threads(threadcount);
    starttime = Millisecs();
    for (int n = 0; n < threadcount; ++n)
    {
       threads[n] = CreateThread(std::bind(CalcPrimeNumbers, range / threadcount * n, range / threadcount, mresults[n]), true);
    }
    for (int n = 0; n < threadcount; ++n)
    {
        threads[n]->Wait();
    }
    elapsed = Millisecs() - starttime;
    Print(String(elapsed) + " milliseconds");

    return 0;
}