High CPU usage while using SFML with multiple threads

Question

I'm using SFML threads, and this makes very high CPU usage.

When only main thread is running, CPU usage is only 1 %, but when 2 threads run, CPU gets as high as 25 %, 3 threads - 50% and so on!!

My CPU has 4 cores, so it seems that each additional thread consumes the whole core!

Why this happens, with 1 thread adding 25% CPU?

It's nothing related to the framerate or sf::sleep(), they make no effect to CPU.

There's a little experimental program which shows everything. When running this code CPU is 25%. When using addidional threads (commented) then goes as high as 75 %.

#include <iostream>
#include <string>
#include <fstream>
#include <SFML/Graphics.hpp>
#include <SFML/System.hpp>

using namespace std;

sf::RenderWindow window;
sf::Event ev;

bool areEvents=false;
bool Window_Closed=false;


void drawZumthin()
{
for(int i=0; i<4; i++)
{
    sf::CircleShape shape(50);
    shape.setFillColor(sf::Color::Green);
    shape.setPosition(i*100,0);

    window.draw(shape);
}
}

void threadOne(int num)
{
long i=0;
while(1)
{
    if(i==0) cout<<"Thread no. "<<num<<endl;
    //sf::sleep(sf::milliseconds(20));
    i++;
}
}

struct Chunk
{
int type;
int tiles[64];
};

void loadNewChunks()
{
cout<<"Loading Chunks\n";

Chunk chunks[25];

for(int i=0; i<25; i++)
{
    chunks[i].type=i;

    for(int j=0; j<64; j++)
    {
        chunks[i].tiles[j]=j-i;
    }
}
}

void startWind()
{
window.create(sf::VideoMode(400,300),"test");
window.setFramerateLimit(60);

while(window.isOpen())
{
    while(window.pollEvent(ev))
    {
        areEvents=true;

        if(ev.type==sf::Event::Closed)
        {
            window.close();
            Window_Closed=true;
        }
    }

    window.clear();

    drawZumthin();

    window.display();
}
}

void getEvents()
{
cout<<"getEvents started\n";
while(!Window_Closed)
{
    if(areEvents)
    {
        bool newChunk=false;

        if(ev.type==sf::Event::TextEntered)
        {
            if(char(ev.text.unicode)=='w') cout<<"\nUp!\n\n";
            if(char(ev.text.unicode)=='s') cout<<"\nDown!\n\n";
            if(char(ev.text.unicode)=='a') cout<<"\nLeft!\n\n";
            if(char(ev.text.unicode)=='d') cout<<"\nRight!\n\n";

            newChunk=true;
        }

        if(newChunk) loadNewChunks();

        areEvents=false;
    }
}
cout<<"GetEvents Stopped.\n";
}

int main()
{
/*cout<<"Launching experimental threads\n";

sf::Thread thr2(threadOne, 1);
sf::Thread thr3(threadOne, 2);
thr2.launch();
thr3.launch();*/

cout<<"Launching startWind()\n";

sf::Thread thr1(startWind);

thr1.launch();

sf::sleep(sf::seconds(2));

getEvents();

return 0;
}

Please help me with this issue. Thanks!