Thread Abstraction

• threads Virtualize the processor

  • provide Illusion that program runs on machine with inf processors.

    → use scheduler among threads to implement it

  • program can create infinite threads

• each thread has its illusion of own CPU

  • TCB: one TCB per thread, holds execution state

• Threads execute with variable speed

  • 따라서 스레드끼리의 순서에 상관없도록 프로그램을 짜야 한다.

Thread vs Process

Process

• Separate address space
• Expensive creation, switch
• non trivial memory sharing

Threads

• share address space
• light creation, switch
• simple memory sharing

Thread Definition

A thread is a Single execution Sequence that represents a Separately Schedulable task

• Single exec seq: 일련의 inst를 수행한다.
• seperately schedulable task: 언제나 실행할 수 있다.

Implementing Thread?

• infinite processor illusion

Thread Operations

1. thread_create(thread, func, args)
   • create new thread to run func(args)
2. thread_yield()
   • relinquish(포기) processor voluntarily
3. thread_join(thread)
   • wait for the created thread to exit then return
4. thread_exit(exit_code)
   • quit thread, clean up
   • wake joiner

각 스레드별로 속도가 다르다.