What is a race condition, and what is a critical section in concurrent programming?

Short answer

A critical section is code that accesses a mutable shared resource. A race condition occurs when multiple threads compete to access and modify that resource simultaneously without proper synchronization.

Explanation

A classic example is the simple count++ operation. At the machine level it consists of three instructions: (1) read the value from memory into a register; (2) increment it; and (3) write it back to memory. If two threads do this at the same time, they may both read 5, calculate 6, and write 6 instead of 7! This unpredictable data loss is a serious race condition.

Code example

// Unsafe multithreaded code:
int counter = 0;
void increment() {
  counter++; // Non-atomic and causes Race Condition
}

Common mistakes

• Believing that a single line of code (such as x++) is an atomic, thread-safe operation.

Follow-up questions

• Compare Mutex, Semaphore, Spinlock, and Read-Write Lock. When should you choose each?

Sources

• Race condition - Wikipedia