Threads

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Sometimes we need to control and protect some critical sections in the code as the following program illustrates.

Control Access

File: thread3.cpp

#include <iostream>
#include <thread>

using namespace std ;

void thread_function1()
{
   for( int i1=0 ; i1<5 ; i1++ )
    cout << "Thread function1: " << i1 << endl ;

}

void thread_function2()
{
   for( int i1=0 ; i1<5 ; i1++ )
    cout << "Thread function2: " << i1 << endl ;

}


int main()
{
    thread t1( &thread_function1 );   // t1 starts running
    thread t2( &thread_function2 );   // t2 starts running
    //cout << "main thread\n";

    // main thread waits for the thread t1 to finish
    t1.join();
    t2.join();



    return 0;
}
Output:
$ rm a.exe ; g++ thread3.cpp ; ./a.exe
Thread function1: Thread function2: 00

Thread function1: Thread function2: 11

Thread function1: Thread function2: 22

Thread function1: Thread function2: 33

Thread function1: Thread function2: 44

We notice that the output from the 2
threads is intermingled. Let's correct this issue
by making sure that only one thread executes a "cout"
at a time.