MultithreadingTutorial

Professor: Shu-Ching ChenTA: Hsin-Yu Ha

What is a Thread?

An independent stream of instructions that can be scheduled to run

A path of execution

int a, b;int c;a = 1;b = a + 2;c = 3;

Seq

uen

tially execute

int a, b;

a = 1;b = a + 2;

int c;

c = 5;

CPU

Multi-ThreadSingle-Thread

CPU

Program v.s. Process v.s. Thread

Program An execution file stored in the harddrive

Process An execution file stored in the Memory

Thread An execution path of part of the process

HDD Memory

Program Process Thread

Why is thread?

Parallel execution Shared resources Easier to create and destroy than

processes (100X) Easy porting to multiple CPUs

The Pthread API

Standardized C language threads programming interface for UNIX systems

Four major groups Thread management: Routines that work directly

on threads - creating, detaching, joining, etc. Mutex: Routines that deal with synchronization.

Mutex functions provide for creating, destroying, locking and unlocking mutexes.

Condition variable: Routines that address communications between threads that share a mutex.

Synchronization: Routines that manage read/write locks and barriers.

Creating threads (1)

pthread_create() Return 0 if OK, nonzero on error

Four Arguments▪ Thread : A thread identifier▪ Attr : A pointer to a thread attribute object ▪ Start_routine : A pointer to the function the thread

executes▪ Arg : The argument to the function

Creating threads (2)

Single variable

Creating threads (3)

Several variables

Terminating Threads (1)

pthread_exit() Return 0 if OK, nonzero on error

Four ways of terminating a thread The thread returns from its starting routine The thread makes a call to the pthread_exit

subroutine The thread is canceled by another thread The entire process is terminated If main() finishes first, without

calling pthread_exit

Terminating Threads (2)

Example of pthread_exit()

Terminating Threads (3)

pthread_join() Return 0 if OK, nonzero on error

Wait from other threads to terminate by calling it

Terminating Threads (4)

Other Thread functions

pthread_self() It returns the unique, system assigned thread ID of the

calling thread

pthread_detach() Return 0 if OK, nonzero on error It can be used to explicitly detach a thread

Synchronizations

Join Mutexes Condition variables

Synchronization - Mutexes (1)

Mutexes are used to prevent data inconsistencies due to

operations by multiple threads upon the same memory area performed at the same time

to prevent race conditions where an order of operation upon the memory is expected

Synchronization - Mutexes (2)

Synchronization - Mutexes (3)

Synchronization – Condition Variables (1)

Condition variables are used to allow threads to synchronize based upon the

actual value of data without continually polling to check whether the condition if met

in conjunction with a mutex lock

Synchronization – Condition Variables (2)

References

POSIX Threads Programming https://computing.llnl.gov/tutorials/pthre

ads/

Pthreads primer http://pages.cs.wisc.edu/~

travitch/pthreads_primer.htmlPOSIX thread (pthread) Tutorial

http://www.yolinux.com/TUTORIALS/LinuxTutorialPosixThreads.html

More tutorial and sample codecan be found…

Tutorial- Wiki http://en.wikibooks.org/wiki/C%2B%2B_Programming/Threading

Tutorial and sample code- C++ Multithreading http://www.tutorialspoint.com/cplusplus/cpp_multithreading.htm- Multithreading pthread http://www.bogotobogo.com/cplusplus/multithreading_pthread.php- Posix threads C http://codebase.eu/tutorial/posix-threads-c/ - Code project http://www.codeproject.com/Articles/14746/Multithreading-Tutorial

Tutorial Youtube Video- C++ Multithreading Pt. 1 http://youtu.be/o9ToXNdHANE- C++ Multithreading Pt. 2 http://youtu.be/a4mRwxWBJxA