What is synchronization in reference to a thread?

Thread synchronization is a fundamental concept in multithreaded programming primarily used to coordinate the execution order of multiple threads sharing resources, preventing data races and ensuring data consistency and correctness.

In multithreaded programs, threads are the basic units scheduled by the operating system, enabling multiple threads to execute concurrently to enhance program performance. However, when multiple threads need to access the same resource (such as memory data), without adequate coordination, conflicts can occur where one thread's operation interferes with another's, which is known as a "race condition" (Race Condition).

To address this issue, thread synchronization mechanisms must be employed. Common thread synchronization techniques include mutexes (Mutex), semaphores (Semaphore), events (Event), etc.

Example:

Consider a simple bank account class that includes deposit and withdrawal operations. If two threads simultaneously operate on a single account object—one performing a deposit and the other a withdrawal—and these operations lack synchronization, it may result in an incorrect final balance for the account.

csharp
public class BankAccount
{
    private object lockObject = new object();
    public int Balance { get; private set; }

    public void Deposit(int amount)
    {
        lock (lockObject)
        {
            Balance += amount;
        }
    }

    public void Withdraw(int amount)
    {
        lock (lockObject)
        {
            if (Balance >= amount)
            {
                Balance -= amount;
            }
        }
    }
}

In this example, we use the lock keyword in C#, which is a simplified implementation based on mutexes. By locking a shared object (here, lockObject), we ensure that only one thread can execute the code block within the Deposit or Withdraw methods at any time, thereby ensuring thread safety.

Thus, no matter how many threads simultaneously access the methods of the same BankAccount instance, the thread synchronization mechanism prevents calculation errors or data inconsistencies.