How to Start a Thread that Runs a Member Function in C++

Running a member function in a thread is more complex, but in C++, creating and managing threads for concurrent execution is made possible through std::thread. Also, handling the threads, needs various measures and methods. In this article, we will discuss the std::thread and member functions, methods to run a member function in threads, handling thread execution, and thread safety considerations.

Table of Contents:

• Understanding std::thread and Member Functions in C++
• How to use std::thread with a Member Function in C++
  • Using a Pointer to a Member Function
  • Using std::bind
  • Using a Lambda Function
• Handling Thread Execution in C++
  • Using join()
  • Using detach()
• Thread Safety Considerations in C++
• Conclusion

Understanding std::thread and Member Functions in C++

In C++, creating and managing threads for concurrent execution is made possible through std::thread. However, running a member function in a thread is more complex because, in contrast to static functions, a non-static member function is always called with an implicit “this pointer”, which means an object of the class must be specified for calling it. Thus, passing a member function to std::thread requires explicit specification of an instance of that class. Among the most common ways to start a thread is by using a pointer to a member function, std::bind, or making use of a lambda function to ensure correct invocation.

How to use std::thread with a Member Function in C++

As the non-static member functions in C++ need an instance of the class, they cannot be directly passed to std::thread like regular functions.

Below are three common methods for running a member function in a thread:

1. Using a Pointer to a Member Function

When you need to pass a member function to std::thread, you must provide both the function pointer and an instance of the class. As the non-static member functions in C++ need an implicit “this pointer”, you must pass the objects of the function explicitly.

Example:

Output:

The code shows how a thread is started using a pointer to run a member function MyClass::memberFunction, and waits for the complete execution using join().

2. Using std::bind

The std::bind in C++ provides you the ability to create an object that can be called through binding a member function to a particular instance of a class. This method is used to simplify the syntax while starting a thread by encapsulating the member function and its related object.

Example:

Output:

The code shows how a thread is started using the std::bind to run a member function of MyClass, and waits for the complete execution using join().

3. Using a Lambda Function

Lambda function in C++ allows you to create an anonymous function that can easily capture variables from the surrounding scope, thus making it very useful to run the member functions in a separate thread without using the std::bind. Also, you can easily capture the class instance by reference or by value for directly calling the member function.

Example:

Output:

The code shows how the two threads can be started using the lambda functions with the different durations to call the member function of MyClass.

Handling Thread Execution in C++

For the proper execution of in C++, it is important to make sure that the resources are managed properly and the program does not give any error. There are two main methods for handling the thread execution: join() and detach().

1. Using join()

You can use the join() method to handle the thread, as it restricts the calling thread until the thread used by the std::thread object has completed its execution. This method is important for getting the confirmation that all the threads have finished their tasks before the termination of the program. If you fail to call join() on a thread that is still running, it can lead to memory leaks and program termination.

Example:

Output:

The code shows a thread is started to run the MyClass::memberFunction with the value of 42 and also waits for the completion of the execution using join() before the main thread is completed.

2. Using detach()

The detach() method in C++ allows you to run a thread independently from the main thread, and once the thread is detached, it continues its execution in the background, and the main thread does not wait for that thread to finish its execution. Thus, using detach() needs awareness for accessing resources because it can lead to the undefined errors before the thread completes its execution.

Example:

Output:

The code shows how a detached thread is started to run the MyClass::memberFunction with the value of 42, having the independent execution when the main thread sleeps for 3 seconds before completing its execution.

Thread Safety Considerations in C++

1. You should use the std::mutex to prevent race conditions while synchronizing the access to the shared resources.
2. Always check that the multiple threads are not modifying the shared variables at the same time to avoid the data race.
3. You must use the std::atomic to provide the lock-free, thread-safe operations.
4. You should reduce the state of shared threads to avoid race conditions and the synchronization issues.
5. Always lock the resources in the same consistent order and use std::lock to avoid deadlocks.
6. You must handle the threads properly using the join() and detach() to confirm the complete execution of the threads to avoid resource leaks.

Conclusion

Starting a thread in C++ that runs a member function needs the understanding of proper handling of class instances and thread execution. By using methods such as the pointers to member functions, std::bind, and lambda functions, you can easily create threads to run a member function. And, handling the thread execution with join() and detach() provides the proper execution and resource management. Thus, understanding threads and how to create them to run a member function is important for developing multithreaded applications.

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