Operating Systems (Threads)

Question 1

Benefits of Single and Multi-treaded processes

Answer 1

1) Responsiveness
2) Resource sharing
3) Economy
4) Utilization of MP architectures

Question 2

Parallel and concurrent systems, and modern CPUs

Answer 2

Parallel system - Performs more than one task simultaneously

Concurrent - Supports more than one task by allowing all tasks to make progress.

Modern CPUs support two or more threads per core

Question 3

User threads are managed by thread libraries, like?

Answer 3

POSIX Pthreads, Win32 threads, and Java threads

Question 4

Kernel Threads are supported and managed directly by?

Answer 4

The OS kernel

e.g.,
• Windows XP/2000
• Solaris
• Linux
• Tru64 UNIX
• Mac OS X

Question 5

Types of multi-threading models? (3)

Answer 5

1) Many-to-one
2) One-to-one
3) Many-to-many

Refers to the number of kernel threads : user threads

Question 6

Examples of OS kernels classified by multi-threading model

Answer 6

• Many-to-One
  
  • Solaris Green Threads
  • GNU Portable Threads
• One-to-One
  
  • Windows NT/XP/2000
  • Linux
  • Solaris 9 and later

• Many-to-Many
• Solaris prior to version 9
• Windows NT/2000 with the ThreadFiber
package

 Two-level
     • IRIX
     • HP-UX
     • Tru64 UNIX
     • Solaris 8 and earlier

Question 7

Two-level multi-threading model?

Answer 7

1st level: Many-to-many

2nd level: one-to-one

Question 8

Function of thread libraries

Answer 8

Provide programmer with an API for library in user space or a kernel library.

Java thread API generally
implemented using a thread library
available on the host system

Question 9

Threading Issues (6)

Answer 9

• fork() and exec() system calls
• Thread cancellation
• Signal handling
• Thread pools
• Thread specific data
• Scheduler activations

Question 10

Thread Pools

Answer 10

• Create a number of threads in a pool
where they await work
• Advantages:
• Slightly faster
• Can bound number of threads in app

Question 11

Signal Handling 1) Purpose, 2) Types, 3) Options

Answer 11

Signals are used in UNIX systems to notify a process
that a particular event has occurred
• Synchronous signal - delivered to process that
executed the event that caused the signal e.g.,
illegal memory access / division by 0
• Asynchronous signal - generated by an event
external to the running process
• Options:
• Deliver the signal to the thread to which the signal applies
• Deliver the signal to every thread in the process
• Deliver the signal to certain threads in the process
• Assign a specific thread to receive all signals for the process

Question 12

Thread Cancellation 1) Meaning, 2) Types

Answer 12

Terminating a thread before it has finished
• Two general approaches:
• Asynchronous cancellation
• Deferred cancellation

Question 13

Thread Specific Data: 1) What is it and why?

Answer 13

Each thread can have its own copy of
data, which is useful when you do not have control
over the thread creation process

Question 14

Scheduler Activations and upcalls

Answer 14

• Both M:M and Two-level models
• require communication to maintain
the appropriate number of kernel
threads allocated to the application
• Scheduler activations provide upcalls
• a communication mechanism from
the kernel to the thread library

Examples: (Could just by multi-thread model)
• Pthreads
• Windows XP
• Linux
• Java

Question 15

Java Thread States

Answer 15

New, then can alternate between Runnable and Blocked (I/O sleep or I/O is available) , then Dead after termination.