L-1.12: User Level Vs Kernel Level Thread in Operating System | All Imp Points

Summary

This video explains the differences between user-level and kernel-level threads, focusing on their management, speed, and behavior. User-level threads are managed by user libraries and are faster to create and switch between, but if one thread blocks, the entire process gets blocked. Kernel-level threads are managed by the OS, involve system calls, and are slower in context switching. However, if a kernel thread blocks, only that specific thread is affected. The video also introduces the concept of hybrid models that combine both types of threads for more efficient resource management.

Takeaways

• 😀 User-level threads (ULTs) are managed by user-level libraries, making the application responsible for creating and controlling them.
• 😀 Kernel-level threads (KLTs) are managed by the operating system kernel, requiring system calls for creation and management.
• 😀 Creating user-level threads is faster because it avoids kernel involvement and uses application-level procedures.
• 😀 Creating kernel-level threads is slower due to system call overhead and kernel involvement.
• 😀 Context switching between user-level threads is faster since it does not require kernel intervention and only saves minimal state information.
• 😀 Context switching between kernel-level threads is slower because it involves the operating system and more complex state management.
• 😀 If a user-level thread performs a blocking operation (like I/O), the entire process is blocked because the kernel is unaware of individual threads.
• 😀 If a kernel-level thread performs a blocking operation, other threads in the same process continue executing, avoiding full process blockage.
• 😀 Both user-level and kernel-level threads share code and data segments but have their own stack and register sets, qualifying them as lightweight processes.
• 😀 Modern systems often use hybrid models (many-to-one, one-to-one, many-to-many) to map user-level threads to kernel-level threads and resolve blocking issues.
• 😀 Competitive exams often focus on thread creation speed, context switching time, blocking behavior, and resource sharing differences between ULTs and KLTs.

Q & A

What is the difference between user level threads and kernel level threads?

User level threads are managed by the user-level library and created by the application itself, while kernel level threads are managed by the operating system. This difference impacts their speed, context switching, and the way they handle blocking operations.

Why are user level threads faster than kernel level threads?

User level threads are faster because they don’t require system calls or operating system intervention. Their creation and management are handled by the application itself, making the process quicker.

What role does the operating system play in kernel level threads?

The operating system (OS) plays a crucial role in kernel level threads by managing them. The creation and management of these threads require system calls, which adds overhead and time compared to user level threads.

How does context switching differ between user level and kernel level threads?

Context switching is faster for user level threads because it doesn’t require the operating system's involvement. In contrast, kernel level thread context switching is slower because it requires the OS to save and load the state of the threads.

What happens when a user level thread performs a blocking operation?

When a user level thread performs a blocking operation, such as I/O tasks, the entire process is blocked because the operating system is unaware of the threads managed by the user-level library.

How does kernel level thread blocking differ from user level thread blocking?

In kernel level threads, if one thread blocks, other threads within the same process can still run, as the OS manages dependencies. However, in user level threads, if one thread blocks, the entire process gets blocked.

What is a hybrid threading model?

A hybrid threading model uses both user level and kernel level threads to combine the benefits of both. It maps multiple user level threads to a smaller number of kernel level threads, which can be done in models like 'many-to-one,' 'many-to-many,' or 'one-to-one'.

Why is the hybrid model advantageous?

The hybrid model is advantageous because it allows systems to take advantage of both the speed of user level threads and the flexibility of kernel level threads. This model can resolve some of the problems associated with thread blocking and context switching.

Do kernel level threads and user level threads share code and data?

Yes, both kernel level and user level threads share code and data. The key difference is that they each have their own registers and stack. This makes them 'lightweight' processes compared to full processes.

In competitive exams, what is commonly tested regarding user level and kernel level threads?

In competitive exams, such as GATE, the primary focus is on understanding the key differences between user level and kernel level threads, particularly their speed, context switching, and handling of blocking operations.