[OS] Threads 2

Threads Part 2

Multithreading Models

• One-to-One
• Many-to-One
• Many-to-Many

One-to-One

• Each user-level thread maps to kernel thread
• Creating a user-level thread creates a kernel thread
• More concurrency than Many-to-One
• Number of threads per process sometimes restricted due to overhead

Many-to-One

• Many user-level threads mapped to single kernel thread
• Small and fast context switch between user threads
• One thread blocking causes all threads to block (kernel thread don’t care)
• Multiple threads may not run in parallel on a multicore system because only one may be in kernel at a time
• Few systems currently use this model

Many-to-Many

• Allows many user level threads to be mapped to many kernel threads
• Allows the operating system to create a sufficient number of kernel threads

Two-level Model

• Similar to Many-to-Many, except that it also allows a user thread to be bound to kernel thread