#include <atomic>
#include <chrono>
#include <condition_variable>
#include <functional>
#include <future>
#include <iostream>
#include <mutex>
#include <queue>
#include <thread>
#include <unordered_map>
#include <vector>

class ThreadPool {
 public:
  // Construct the ThreadPool with a specified number of worker threads.
  explicit ThreadPool(size_t numThreads) : stopSignal(false) {
    for (size_t i = 0; i < numThreads; ++i) {
      workers.emplace_back([this] {
        while (true) {
          std::function<void()> task;
          {
            // Acquire lock to access the queue
            std::unique_lock<std::mutex> lock(this->queueMutex);

            // Block until there is a task or the pool is stopping
            this->condition.wait(lock, [this] {
              return this->stopSignal || !this->tasks.empty();
            });

            // If stopSignal is true and no tasks remain, exit worker thread
            if (this->stopSignal && this->tasks.empty()) {
              return;
            }

            // Pop a task from the queue
            task = std::move(this->tasks.front());
            this->tasks.pop();
          }
          // Execute the task outside the lock
          task();
        }
      });
    }
  }

  // Add a task to be executed by the pool
  template <typename F, typename... Args>
  auto enqueue(F&& f, Args&&... args)
    -> std::future<typename std::result_of<F(Args...)>::type> {
    using returnType = typename std::result_of<F(Args...)>::type;

    // Create a task packaged as a future
    auto taskPtr = std::make_shared<std::packaged_task<returnType()>>(
      std::bind(std::forward<F>(f), std::forward<Args>(args)...));

    std::future<returnType> result = taskPtr->get_future();
    {
      std::unique_lock<std::mutex> lock(queueMutex);

      // Do not allow enqueueing after stopping
      if (stopSignal)
        throw std::runtime_error("enqueue on stopped ThreadPool");

      // Add the task to the queue
      tasks.emplace([taskPtr]() { (*taskPtr)(); });
    }
    condition.notify_one();
    return result;
  }

  // Destructor joins all threads
  ~ThreadPool() {
    {
      std::unique_lock<std::mutex> lock(queueMutex);
      stopSignal = true;
    }
    condition.notify_all();
    for (std::thread& worker : workers) {
      if (worker.joinable()) {
        worker.join();
      }
    }
  }

 private:
  // Vector to hold worker threads
  std::vector<std::thread> workers;
  // Task queue
  std::queue<std::function<void()>> tasks;

  // Synchronization
  std::mutex queueMutex;
  std::condition_variable condition;

  // Stop signal
  bool stopSignal;
};

int main() {
  // Create a pool with 4 worker threads
  ThreadPool pool(4);
  // Run 100 tasks on the thread pool
  for (size_t taskId = 1; taskId <= 100; ++taskId) {
    pool.enqueue([taskId] {
      std::cout << "Task " << taskId << " is being executed by thread "
                << std::this_thread::get_id() << std::endl;
      std::this_thread::sleep_for(std::chrono::milliseconds(5));
    });
  }

  return 0;
}

C++ Online Compiler

Write, Run & Share C++ code online using OneCompiler's C++ online compiler for free. It's one of the robust, feature-rich online compilers for C++ language, running on the latest version 17. Getting started with the OneCompiler's C++ compiler is simple and pretty fast. The editor shows sample boilerplate code when you choose language as C++ and start coding!

Read inputs from stdin

OneCompiler's C++ online compiler supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample program which takes name as input and print your name with hello.

#include <iostream>
#include <string>
using namespace std;

int main() 
{
    string name;
    cout << "Enter name:";
    getline (cin, name);
    cout << "Hello " << name;
    return 0;
}

About C++

C++ is a widely used middle-level programming language.

  • Supports different platforms like Windows, various Linux flavours, MacOS etc
  • C++ supports OOPS concepts like Inheritance, Polymorphism, Encapsulation and Abstraction.
  • Case-sensitive
  • C++ is a compiler based language
  • C++ supports structured programming language
  • C++ provides alot of inbuilt functions and also supports dynamic memory allocation.
  • Like C, C++ also allows you to play with memory using Pointers.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition If-Else is used.

if(conditional-expression) {
   //code
}
else {
   //code
}

You can also use if-else for nested Ifs and If-Else-If ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to If-Else-If ladder.

switch(conditional-expression){    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
......    
    
default:     
 code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  //code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while (condition) {  
// code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {  
 // code 
} while (condition);

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity. Function gets run only when it is called.

How to declare a Function:

return_type function_name(parameters);

How to call a Function:

function_name (parameters)

How to define a Function:

return_type function_name(parameters) {  
 // code
}