C++11 Multithreading – Part 1 : Three Different ways to Create Threads

C++11 Multithreading – Part 1 : Three Different ways to Create Thread

In this article we will learn to create threads in C++ using std::thread.

• Creating a thread using Function Pointer 
• Creating a thread using Function Objects
• Creating a thread using Lambda functions

Overview C++11 Thread Library :

Original C++ only uses one single thread programming, but in 2011 a new C++11 introduced which contains new thread library.

Prerequisite compilers:

• Linux: gcc 4.8.1 (Complete Concurrency support)
• Windows: Visual Studio 2012 and MingW

Thread Creation in C++11

In C++11 in addition to default main thread we can produce additional threads by creating objects of std::thread::class.

What std::thread accepts in constructor ?

If we attach a callback with std::thread object, then that will be executed when new thread starts execution. New thread will be start after creation of object. Any thread can wait for other by calling join() on that thread’s object.

Creating a thread using Function Pointer :

#include <iostream>
#include <thread>
 
void thr_func()
{
    for(int x = 0; x < 100; x++);
        std::cout<<"thread function is running"<<std::endl;
}
 
int main()  
{
    
    std::thread thrObj(thr_func);
    for(int x = 0; x < 100; x++);
        std::cout<<"MainThread executing"<<std::endl;
    thrObj.join();    
    std::cout<<"End of Main function"<<std::endl;
    return 0;
}

Output :
MainThread executingthread function is running
End of Main function

Creating a thread using Function Objects :

#include <iostream>
#include <thread>
class DisThr
{
public:
    void operator()()     
    {
        for(int x = 0; x < 5; x++)
            std::cout<<"Display Thread"<<std::endl;
    }
};
 
int main()  
{
    std::thread thrObj( (DisThr()) );
    for(int x = 0; x < 5; x++)
        std::cout<<"Main thread"<<std::endl;
    std::cout<<"Waiting for thread to complete..."<<std::endl;
    thrObj.join();
    std::cout<<"Main Thread completes execution"<<std::endl;
    return 0;
}

Output :
Main threadDisplay Thread
Display Thread
Display Thread
Display Thread
Display Thread
Main thread
Main thread
Main thread
Main thread
Waiting for thread to complete...
Main Thread completes execution

Creating a thread using Lambda functions :

#include <iostream>
#include <thread>
int main()  
{
    int a = 9;
    std::thread thrObj([]{
            for(int x = 0; x < 5; x++)
                std::cout<<"Display Thread"<<std::endl;
            });
            
    for(int x = 0; x< 5; x++)
        std::cout<<"Main Thread"<<std::endl;
        
    thrObj.join();
    std::cout<<"Main Thread completes execution"<<std::endl;
    return 0;
}

Output :
Main ThreadDisplay Thread
Display Thread
Display Thread
Display Thread
Main Thread
Main Thread
Main Thread
Main Thread
Display Thread
Main Thread completes execution

Differentiating between threads

Each std::thread object has an associated ID and we can fetch it using following syntax: std::thread::get_id().

#include <iostream>
#include <thread>
void thr_func()
{
    std::cout<<"Inside Thread that has ID  = "<<std::this_thread::get_id()<<std::endl;    
}
int main()  
{
    std::thread thrObj1(thr_func);
    std::thread thrObj2(thr_func);
 
    if(thrObj1.get_id() != thrObj2.get_id())
        std::cout<<"IDs of both threads are different"<<std::endl;
 
        std::cout<<"ID of Thread1 in main thread = "<<thrObj1.get_id()<<std::endl;    
    std::cout<<"ID of Thread2 in main thread = "<<thrObj2.get_id()<<std::endl;    
 
    thrObj1.join();    
    thrObj2.join();    
    return 0;
}

Output :
IDs of both threads are different
ID of Thread1 in main thread = 140250265655040
ID of Thread2 in main thread = 140250257262336
Inside Thread that has ID  = 140250265655040
Inside Thread that has ID  = 140250257262336