Operating System notes: Threads

4th Chapter: Threading

• What is it?
  
  Basic unit used by CPU
• Composition
  
  Thread ID, program counter, register collection, stack

Multithreading Benefits

• High degree of responsiveness
• Resource sharing
• Economic
• Utilization of multi-processor architectures

Multithreaded models provide methods that are supported by threads:

• User thread
• Kernel threads

Three types of models

Model	Concept	features
Many-to-one	Mapping many user threads to a kernel thread	A thread is blocked, the process is blocked, and cannot be run concurrently on multiple processors
One	Map each user thread to a kernel thread	One thread is blocked, another thread can run, can run concurrently on multiple processors, and resource overhead is high
Many-to-many	Multiplexing to the same number or fewer kernel threads	Combine the advantages of both

Cancellation of the thread

• Asynchronous cancellation: A thread terminates immediately
• Deferred cancellation: Allows threads to terminate in an orderly manner

Cancel Point

Signal Processing mode:

• The signal is generated by the occurrence of a particular event.
• The resulting signal to be sent to the process
• Once sent, the signal must be processed

Question:

1. Describe the actions taken by the line libraries in the process of user-level process context switching?
   
   
2. What parts of the following programs are shared by threads in multithreaded programs? A. Deposit Value B. Heap memory c. global variable D. Stack memory
   
   A threaded thread is shared with heap memory and global variables, but each thread has its own value for storage and stack memory

Operating System notes: Threads