Ask how to share thread data

Finder.cpp

#include "Finder.h"
#include <algorithm>
#include <random>
#include <chrono>
#include <thread>
#include <string>

FinderForTx::FinderForTx()
{
}

FinderForTx::~FinderForTx()
{
}

OutputTx FinderForTx::findPred(InputTx &inputVec)
{
	default_random_engine dre(random_device{}());
	uniform_int_distribution<int> id(1, 20);
	this_thread::sleep_for(chrono::milliseconds(id(dre)));
	OutputTx output;
	output.strNumber = to_string(inputVec.number);
	return output;
}

void FinderForBlock::execute(vector<InputTx> *inputVec, vector<OutputTx> *outputVec)
{
	FinderForTx finder;
	for (size_t i = 0; i<inputVec->size(); i++)
	{
		outputVec->at(i) = finder.findPred(inputVec->at(i));
	}
}

vector<OutputTx> FinderForBlock::findPred(vector<InputTx> &inputVec)
{
	vector<OutputTx> outputVec;
	outputVec.resize(inputVec.size());
	if (nThreads == 0)
	{
		FinderForTx finder;
		for (size_t i = 0; i<inputVec.size(); i++)
		{
			outputVec[i] = finder.findPred(inputVec[i]);
		}
	}
	else
	{
		vector<thread> vec_thr;
		for (int i=0; i<nThreads; i++)
			vec_thr.emplace_back(&execute, &inputVec, &outputVec);
		for (auto& t : vec_thr)
			t.join();
	}
	return outputVec;
}

Finder.h

/*see:
http://www.cplusplus.com/forum/unices/194352/ - vector of threads, no mutex example
http://deathbytape.com/articles/2015/02/03/cpp-threading.html - lock_guard<mutex>, main thread + one thread, mutex is global
*/
#pragma once
#include <vector>
using namespace std;

struct InputTx
{
	int number;
};

struct OutputTx
{
	string strNumber;
};

class FinderForTx
{
public:
	FinderForTx();
	virtual ~FinderForTx();
	OutputTx findPred(InputTx &inputVec);
};

class FinderForBlock
{
	int nThreads;
	static void execute(vector<InputTx> *inputVec, vector<OutputTx> *outputVec);
public:
	FinderForBlock(int nThreads) :nThreads(nThreads) {};
	virtual ~FinderForBlock(){};
	vector<OutputTx> findPred(vector<InputTx> &inputVec);
};

main.cpp

#include "Finder.h"
#include <random>
#include <string>

void gen(vector<InputTx> &inputVec)
{
	default_random_engine dre(0);
	uniform_int_distribution<int> id(1, 100);
	for (int i=0; i<100; i++)
	{
		InputTx input;
		input.number = id(dre);
		inputVec.push_back(input);
	}
}

void check(vector<InputTx> &inputVec, vector<OutputTx> &outputVec)
{
	if (inputVec.size() != outputVec.size())
	{
		printf("sizes mismatch!\n");
		return;
	}
	for (size_t i=0; i<inputVec.size(); i++)
		if (to_string(inputVec[i].number)!= outputVec[i].strNumber)
		{
			printf("number[%d] %d changed to [%s]\n", i,inputVec[i].number, outputVec[i].strNumber.c_str());
			return;
		}
}

int main()
{
	vector<InputTx> inputVec;
	gen(inputVec);	
	FinderForBlock finder(2);
	vector<OutputTx> outputVec = finder.findPred(inputVec);
	check(inputVec, outputVec);
    return 0;
}