threads

1. THREADS
By N.B.SHETTY

2. INTRODUCTION
 A thread is contained Process and threads
inside a process and
different threads in the
same process share some
resources (most
commonly memory),
while different processes
do not.

3. INTRODUCTION
 A thread is a basic unit of CPU utilization, consisting
of a program counter, a stack, and a set of
registers, ( and a thread ID. )
 On a single processor, multithreading generally
occurs by as in multitasking, the processor
switches between different threads.
 On a multiprocessor or multi-core system, the
threads or tasks actually do run at the same time,
with each processor or core running a particular
thread or task

4. SINGLE AND MULTI THREAD

5.  Single Thread
 Has single thread of control
 It allows the process to perform only 1 task at a time.
 Multi thread
 Has many threads
 Simultaneous execution of different task

6. BENEFITS
 Take less time to create a new tread than a process.
 Less time to terminate a tread than a presses.
 less time to switch between two treads within the same
process.
 Hence treads within the same process share memory and
files, they can communicate with each other without
invoking the kernel.
 Responsiveness.
 Resource sharing .
 Economy.
 Utilization of MP Architectures.

7. User Threads
 Thread management done by user-level threads
library
 Thread creation, scheduling, are done in user level
 Fast to create and manage
 Drawback:
 If kernel is single thread, then user level thread
performing a blocking system call will cause entire
process to block

8. KERNEL THREAD
 Supported by OS
 Thread creation, scheduling, are done in user level by
kernel
 Thread management is performed by os, thus
kernel thread are slow.
 If thread perform blocking system call, kernel can
schedule another thread in application for
execution

9. Multithreading Models
(In a specific implementation, the user threads
must be mapped to kernel threads, using one
of the following strategies. )
Many-to-One
One-to-One
Many-to-Many

10. MANY-TO-ONE
 many user-level threads are
all mapped onto a single
kernel thread.
 Thread management is
handled by the thread library
in user space, which is very
efficient.
 if a blocking system call is
made, then the entire process
blocks, even if the other user
threads would otherwise be
able to continue.
 Ex: Green threads for Solaris
and GNU Portable

11. ONE-TO-ONE MODEL
 Each user-level thread maps to kernel thread
 Allow anther thread to run if block
 Run parallel
 Drawback: along with user thread kernel thread shld be
created.
 Ex: Linux and Windows from 95 to XP

12. MANY-TO-MANY
 The many-to-many model
multiplexes any number of user
threads onto an equal or
smaller number of kernel
threads, combining the best
features of the one-to-one and
many-to-one models.
 Blocking kernel system calls do
not block the entire process.
 Individual processes may be
allocated variable numbers of
kernel threads, depending on
the number of CPUs present
and other factors.
 Ex: RIX, HP-UX, and Tru64
UNIX

13. Thread Libraries
 Thread libraries provide programmers with an API
for creating and managing threads.
 Thread libraries may be implemented either in user
space or in kernel space.
 There are three main thread libraries in use today:
 POSIX Pthreads .
 Win32 threads.
 Java threads .

14. Pthreads
 May be provided either as user-level or kernel-level.
 A POSIX standard (IEEE 1003.1c) API for thread
creation and synchronization.
 API specifies behavior of the thread library,
implementation is up to development of the library.
 Common in UNIX operating systems (Solaris,
Linux, Mac OS X).

15. Linux Threads
 Linux refers to them as tasks rather than
threads.
 Thread creation is done through clone()
system call.
 clone() allows a child task to share the
address space of the parent task (process).