Process Management -Threads

Threads

is a basic unit of CPU utilization

Benefits

Responsiveness - may allow continued execution if part of process is blocked, especially important for user interfaces • Resource Sharing - threads share resources of process, easier than shared memory or message passing • Economy - cheaper than process creation, thread switching lower overhead than context switching • Scalability - process can take advantage of multiprocessor architectures

Kernels are generally multi-threaded

Multicore Programming Challenges

Identifying tasks, Balance, Data splitting, Data dependency, Testing and debugging

Parallelism

implies a system can perform more than one task simultaneously

Concurrency

supports more than one task making progress

Single processor / core, scheduler providing concurrency

Data parallelism

distributes subsets of the same data across multiple cores, same operation on each

Task parallelism

Distributes threads across cores, each thread performing a unique operation

Amdahl's Law

Identifies performance gains from adding additional cores to an application that has both serial and parallel components

S is serial portion

N processing cores

User threads

supported above the kernel and are managed without kernel support

Kernel threads

Supported and managed directly by the OS

Multithreading Models

Many-to-One,

One-to-One,

Many-to-Many

Many-to-One

Many user-level threads mapped to single kernel thread

many-to-one examples

Solaris Green Threads

GNU Portable Threads

One-to-One

Each user-level thread maps to kernel thread

One-to-One examples

Windows

Linux

Solaris 9 and later

Many-to-Many

Many user-level threads mapped to many kernel threads

Many-to-Many examples

Solaris prior to version 9

Windows with the ThreadFiber package

Two - Level Model

Similar to M:M, except that it allows a user thread to be bound to kernel thread

Two - Level Model examples

Tru64 UNIX

Solaris 8 and earlier

A process consisting of n ULTs is to be mapped onto a set of m KLTs. Which combination would not fully utilize available resources?

a. n=m>0

b. n >m = 1

c. m>n>1

d. n>m>1

c. m>n>1

Kernel calls are _ to manage threads.

a. Needed only with KLTs

b. Needed only with ULTs

c. Always needed

d. Never needed

a. Needed only with KLTs

Thread library

provides programmer with API for creating and managing threads

Two primary ways of implementing Thread Library

Library entirely in user space and Kernel-level library supported by the OS

Java Thread

There are two techniques for creating threads in a Java program. One approach is to create a new class that is derived from the Thread class and to override its run() method. An alternative—and more commonly used—

technique is to define a class that implements the Runnable interface.