Threads

Threads

1. What is a 'Thread'?

   • A way for a program to split itself in two or more running tasks
     • Fundamental for CPU utilisation and multithreaded computers
       • Multithreading
         • OS can run multiple threads within a single process
   • a.k.a thread of execution
   • Thread Structure
     • Thread ID
     • Program counter
     • Register set
     • Stack
   • Thread Libraries
     • For Thread Creation and Termination
       • pthread_creat()
       • Pthread_exit()
       • Pthread_detach()
         • Remove data structure

2. Benefits of Threads

   • Thread creation doesn't require OS to initialise resources shared between parent processes and its threads
   • Responsiveness
     • Process can run even if part of it is blocked
       • User can still use it
   • Resource Sharing
     • Several activities within one address space
   • Economy
     • Threads share resources of process
       • More economical to context-switch threads
   • Utlisation of multiprocessor architectures
     • Multiple threads on multiple CPUs
       • Increased concurrency!

3. Thread State

   • State shared by all threads in address space
     • Contents of memory (data, heap)
     • I/O state
   • Private to each thread
     • Kept in Thread Control Block (TCB)

4. Java Threads

   • Extend Thread
   • Implement Runnable

5. Threading Models

   • User-Level Threads
     • Threading operations performed in user space
       • Kernel sees one execution context
       • many-to-one thread mapping
       • Manage own resources
   • Kernel-Level Threads
     • Maps each thread to its own execution context
       • one-to-one thread mapping
     • If one user-level thread is blocked = whole process blocked
   • User-Kernel Combo Model
     • Thread creation done in user space
     • Bulk of scheduling of threads within application

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