User-Level vs Kernel-Level Threads Quiz

Thread Management Models

• OS/2, Windows NT, and Windows 2000 utilize the one-to-one model.
• User-level threads are faster to create and manage, whereas kernel-level threads are slower.
• User-level threads are implemented by a thread library at the user level, whereas kernel-level threads are supported directly by the operating system.
• Kernel-level threads are specific to the operating system, whereas user-level threads are generic and can run on any operating system.
• Multi-threaded applications cannot take advantage of multiprocessing using user-level threads.

Kernel-Level Threads

• Thread management is done by the Kernel.
• No thread management code is in the application area.
• Supported directly by the operating system.
• Scheduling is done on a thread basis by the Kernel.
• Performs thread creation, scheduling, and management in Kernel space.
• Generally slower to create and manage than user threads.

Advantages of Kernel-Level Threads

• Simultaneously schedule multiple threads from the same process on multiple processes.
• If one thread in a process is blocked, the Kernel can schedule another thread of the same process.

Disadvantages of Kernel-Level Threads

• Generally slower to create and manage than user threads.
• Transfer of control from one thread to another within the same process requires a mode switch to the Kernel.

Multi-Threading Models

• Many-to-Many: multiplexes user threads onto a smaller or equal number of kernel threads.
• Many-to-One: many user threads to one Kernel thread.
• One-to-One: each user-level thread corresponds to a kernel-level thread.

Single-Threaded vs. Multi-Threaded Process

• THREAD: multi-threading is the ability of an OS to support multiple, concurrent paths of execution within a single process.

Advantages of Threads

• Minimize context switching time.
• Efficient communication.
• Concurrency within a process.
• Utilization of multiprocessor architectures to a greater scale and efficiency.

Types of Threads

• User-Level Threads: user-managed threads, operate without the involvement of the thread management kernel.
• Kernel-Level Threads: Operating System managed threads, acting on kernel, an operating system core.

Advantages of User-Level Threads

• Thread switching does not require Kernel mode privileges.
• User-level threads can run on any operating system.
• Scheduling can be application-specific in the user level thread.
• User-level threads are fast to create and manage.

Disadvantages of User-Level Threads

• In a typical operating system, most system calls are blocking.
• Multi-threaded application cannot take advantage of multiprocessing.