What is the lock keyword in C#? Why is it needed?

Question

Ponu Maurya · Answer

The lock keyword in C# is used to prevent multiple threads from accessing a critical section of code at the same time. It ensures
thread safety by allowing only one thread at a time to execute the code block inside the
lock.
Why is lock Needed?
In multithreaded applications, if multiple threads read/write shared data simultaneously, it can lead to:
Race conditions (unexpected results)Data corruptionApplication crashes
The lock keyword prevents these problems by synchronizing access to shared resources.
Syntax:
lock (objectName)
{
    // Critical section — only one thread can enter at a time
}
The object used in lock(...) must be shared, and usually private (e.g.,
private readonly object _lock = new object();).This object acts as a mutual exclusion lock (mutex).
Example:
private readonly object _lock = new object();
private int _counter = 0;
public void Increment()
{
    lock (_lock)
    {
        _counter++; // Safely accessed by only one thread at a time
    }
}
If multiple threads call Increment(), the lock ensures that:
One thread waits while another is inside the block.Shared resource _counter is updated safely.
⚠️ What Happens Without lock
_counter++; // Not thread-safe!
Multiple threads might:
Read the same value of _counterIncrement itWrite back an incorrect value
This can cause unexpected behavior, especially in high-concurrency applications.
Good Practices:
Use a private, readonly object as the lock target.Never lock on this or public types — can lead to deadlocks or external interference.Keep the lock block as short as possible to avoid performance bottlenecks.
Summary:
Feature
Description
Keyword
lock
Purpose
Prevent multiple threads from entering a critical section simultaneously
Common use
Shared counters, collections, file writing
Lock target
Private object (object _lock = new object();)
Risk without it
Race conditions, crashes, corrupted data
Also Read:
What is the difference between Task.Run(), Task.Factory.StartNew() and Thread?What is the difference between shallow copy and deep copy?

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What is the lock keyword in C#? Why is it needed?

Anubhav Kumar

Can you answer this question?

1 Answers

Why is `lock` Needed?

Syntax:

Example:

⚠️ What Happens Without `lock`

Good Practices:

Summary:

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Feature	Description
Keyword	`lock`
Purpose	Prevent multiple threads from entering a critical section simultaneously
Common use	Shared counters, collections, file writing
Lock target	Private object (`object _lock = new object();`)
Risk without it	Race conditions, crashes, corrupted data