Thread and concurrency

Thread

Thread is a lightweight process, a basic unit of CPU utilization.

All threads belonging to the same process share:

• Code section.
• Data section.
• OS resources(e.g. open files and signals)

Each thread has its own(thread control block):

• Thread ID.
• Program counter.
• Register set.
• A tack.

Benefits of multithreading:

• Responsiveness.
• Resource sharing.
• Utilization of NP arch.
• Economy.

User vs Kernel threads

User threads

• Thread management is done by the user-level thread library.
• POSIX Pthreads.
• Win32 threads.
• Java threads.
• Thread library provides support for thread creation, scheduling, and deletion.
• Generally fast to create and manage.
• If the kernel is single-threaded, a user-thread block -> entire process blocks even if other threads are ready to run.

Kernel threads

• Supported by the kernel(OS) directly.
• Windows 2000(NT)
• Solaris
• Linux
• Tr64 UNIX
• The kernel performs thread creation, scheduling, etc.
• Generally slower to create and manage.
• If a thread is blocked, the kernel can schedule another thread for execution.

Multithreading models

• Many-to-One: Many user-level threads mapped to a single kernel thread.
• One-to-One: Each user-level thread maps to the kernel thread.
• Many-to-Many:  Multiplexes many user-level threads to a smaller or equal number of kernel threads

Thread pools

Create a number of threads in the pool where they await work.

Advantages:

• Usually slightly faster to service a request with an existing thread than create a new thread.
• Allows the number of threads in the application(s) to be bound to the size of the pool.

reference:

https://www.amazon.com/-/zh_TW/Operating-System-Concepts-Abraham-Silberschatz/dp/1119800366/ref=sr_1_1?keywords=Operating-System-Concepts&qid=1669538704&s=books&sr=1-1