Threading in c++ - c++

Question

Lets say I want to take an input from user and perform a search in a text file for that input. The search will be performed for every character user inputs. There will be a loop performing search and there will be another loop to check if new character is input by the user. Second loop will restart the first loop if new char is given by the user.
Please just explain how to perform above with c++. I think threads need to be created.
Below variables will be used to maintain common values:
static var`
bool change;
while(!change)
{
change=false
<<do something, like search in file>>
}
Other loop will be like below:
while(1)
{
if(user enters another char)
{
var=new value input by the user;
change=true;
}
else change=false;
}
Thanks!

Answer 1

Something like this? Now I wrote this on ideone and their threads didn't work for me so I wasn't able to test it but yeah.. Something close to this should work. Probably a bad example. A thread pool would be best.
#include <iostream>
#include <thread>
#include <atomic>
#include <queue>
#include <mutex>
#include <chrono>
std::mutex lock;
std::atomic<bool> stop(false);
std::queue<std::function<void()>> jobs;
void One()
{
while(!stop)
{
if (!jobs.empty())
{
if (lock.try_lock())
{
std::function<void()> job = jobs.front();
jobs.pop();
lock.unlock();
job();
}
}
std::this_thread::sleep_for(std::chrono::milliseconds(100));
}
}
void Two()
{
std::string var;
while(true)
{
if (std::cin>> var)
{
std::lock_guard<std::mutex> glock(lock);
jobs.push([] {std::cout<<"Task added to the queue..\n";});
}
else
break;
std::this_thread::sleep_for(std::chrono::milliseconds(100));
}
}
int main()
{
std::thread T(One);
Two();
stop = true;
T.join();
return 0;
}

Answer 2

Create two threads: one for reading user-input, and another for performing the search.
Use a binary-semaphore in order to synchronize between the two threads in a Consumer-Producer manner, i.e., one thread acquires the semaphore and the other thread releases it:
static BinarySemaphore binSem;
static int inputCharacter = 0;
static void ReadUserInput();
static void PerformSearch();
void Run()
{
BinarySemaphore_Init(&binSem,0);
CreateThread(ReadUserInput,LOWER_PRIORITY);
CreateThread(PerformSearch,HIGHER_PRIORITY);
}
static void ReadUserInput()
{
while (inputCharacter != '\n')
{
inputCharacter = getc(stdin);
BinarySemaphore_Set(&binSem);
}
}
static void PerformSearch()
{
while (inputCharacter != '\n')
{
BinarySemaphore_Get(&binSem,WAIT_FOREVER);
// <<do something, like search in file>>
}
}
Please note that you need to create the thread which performs the search, with priority higher than that of the thread which reads user-input (as in the code above).