1. Threads and Scheduling
Section 4
Threads and Scheduling
February 10th, 2017
Taught by Josh Don

2. Waiting/Synchronization Context Switching Overhead
Process
Thread
Data/Memory
Communication
Creation
Waiting/Synchronization
Use case
Context Switching Overhead

3. Waiting/Synchronization Context Switching Overhead
Process
Thread
Data/Memory
Independent address space
Communication
Creation
Waiting/Synchronization
Use case
Context Switching Overhead

4. Waiting/Synchronization Context Switching Overhead
Process
Thread
Data/Memory
Independent address space
Shares address space with other threads in same process. Each thread still has own registers and stack
Communication
Creation
Waiting/Synchronization
Use case
Context Switching Overhead

5. Waiting/Synchronization Context Switching Overhead
Process
Thread
Data/Memory
Independent address space
Shares address space with other threads in same process. Each thread still has own registers and stack
Communication
Pipes, files, sockets
High overhead
Creation
Waiting/Synchronization
Use case
Context Switching Overhead

6. Waiting/Synchronization Context Switching Overhead
Process
Thread
Data/Memory
Independent address space
Shares address space with other threads in same process. Each thread still has own registers and stack
Communication
Pipes, files, sockets
High overhead
Read data of another thread
Low overhead
Creation
Waiting/Synchronization
Use case
Context Switching Overhead

7. Waiting/Synchronization Context Switching Overhead
Process
Thread
Data/Memory
Independent address space
Shares address space with other threads in same process. Each thread still has own registers and stack
Communication
Pipes, files, sockets
High overhead
Read data of another thread
Low overhead
Creation
fork()
Higher overhead
Waiting/Synchronization
Use case
Context Switching Overhead

8. Waiting/Synchronization Context Switching Overhead
Process
Thread
Data/Memory
Independent address space
Shares address space with other threads in same process. Each thread still has own registers and stack
Communication
Pipes, files, sockets
High overhead
Read data of another thread
Low overhead
Creation
fork()
Higher overhead
pthread_create()
Lower overhead
Waiting/Synchronization
Use case
Context Switching Overhead

9. Waiting/Synchronization Context Switching Overhead
Process
Thread
Data/Memory
Independent address space
Shares address space with other threads in same process. Each thread still has own registers and stack
Communication
Pipes, files, sockets
High overhead
Read data of another thread
Low overhead
Creation
fork()
Higher overhead
pthread_create()
Lower overhead
Waiting/Synchronization
wait()
Use case
Context Switching Overhead

10. Waiting/Synchronization Context Switching Overhead
Process
Thread
Data/Memory
Independent address space
Shares address space with other threads in same process. Each thread still has own registers and stack
Communication
Pipes, files, sockets
High overhead
Read data of another thread
Low overhead
Creation
fork()
Higher overhead
pthread_create()
Lower overhead
Waiting/Synchronization
wait()
join()
Use case
Context Switching Overhead

11. Waiting/Synchronization Context Switching Overhead
Process
Thread
Data/Memory
Independent address space
Shares address space with other threads in same process. Each thread still has own registers and stack
Communication
Pipes, files, sockets
High overhead
Read data of another thread
Low overhead
Creation
fork()
Higher overhead
pthread_create()
Lower overhead
Waiting/Synchronization
wait()
join()
Use case
Instance of a running program (an executable)
Context Switching Overhead

12. Waiting/Synchronization Context Switching Overhead
Process
Thread
Data/Memory
Independent address space
Shares address space with other threads in same process. Each thread still has own registers and stack
Communication
Pipes, files, sockets
High overhead
Read data of another thread
Low overhead
Creation
fork()
Higher overhead
pthread_create()
Lower overhead
Waiting/Synchronization
wait()
join()
Use case
Instance of a running program (an executable)
Multithreaded process: divide up parallel tasks for a given program
Context Switching Overhead

13. Waiting/Synchronization Context Switching Overhead
Process
Thread
Data/Memory
Independent address space
Shares address space with other threads in same process. Each thread still has own registers and stack
Communication
Pipes, files, sockets
High overhead
Read data of another thread
Low overhead
Creation
fork()
Higher overhead
pthread_create()
Lower overhead
Waiting/Synchronization
wait()
join()
Use case
Instance of a running program (an executable)
Multithreaded process: divide up parallel tasks for a given program
Context Switching Overhead
higher overhead (need to swap memory, page tables, etc.)

14. Waiting/Synchronization Context Switching Overhead
Process
Thread
Data/Memory
Independent address space
Shares address space with other threads in same process. Each thread still has own registers and stack
Communication
Pipes, files, sockets
High overhead
Read data of another thread
Low overhead
Creation
fork()
Higher overhead
pthread_create()
Lower overhead
Waiting/Synchronization
wait()
join()
Use case
Instance of a running program (an executable)
Multithreaded process: divide up parallel tasks for a given program
Context Switching Overhead
higher overhead (need to swap memory, page tables, etc.)
lower overhead (only need to swap thread state)

15. Scheduling
Scheduling: The process by which the kernel chooses the next thread to run
There may be many threads ready to run at any given time
Kernel must choose amongst the ready threads, and start running the chosen thread
The kernel switches very quickly between threads of currently running processes, so everything gets some time to run
A running thread can either yield to the scheduler, or a timer will go off to preempt the running thread
Context Switch: The period during which we stop the current running thread, and load a new thread to run
Priority Scheduling: Every thread is assigned a priority. The scheduler chooses the highest priority ready thread to run

16. Scheduling overview Creation Scheduler exit exit Yield, timer
New
Terminated
Creation
Scheduler
exit
Ready
Running
exit
Zombie
Yield, timer
I/O or syscall completion, lock_release of desired lock, etc.
I/O, syscall, lock_acquire, join/wait, etc.
Waiting