What is a Race Condition?
Updated Feb 20, 2026
Short answer
A race condition occurs when multiple threads access shared data at the same time and the final result depends on the timing of execution.
Deep explanation
In concurrent systems, threads often share memory or resources. If two or more threads try to read and write the same variable without proper synchronization, the outcome becomes unpredictable.
The problem happens because operations like “read → modify → write” are not atomic. If threads interleave these steps, data can get corrupted or overwritten.
To prevent race conditions, synchronization techniques like locks, mutexes, or atomic operations are used.
Real-world example
Two users withdrawing money from the same bank account at the same time:
- Balance = 1000
- User A withdraws 700
- User B withdraws 500
Without synchronization, both might read 1000 and allow withdrawals, leading to negative balance.
Common mistakes
- - Assuming race conditions always crash the program (they often cause silent data errors).
- - Not protecting shared variables in multi-threaded code.
- - Thinking they only happen in complex systems (they can occur in simple counters too).
Follow-up questions
- What is a critical section?
- How do locks prevent race conditions?
- What are atomic operations?