Asg2 Thread Supp

8/2/2019 Asg2 Thread Supp

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THREAD

IMPLEMENTATION

For parallel processing


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Steps involved

Creation

Creates a thread with a thread id.

Detach and Join

All threads must be detached or joinedwith.

Termination

Analogous to exit


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Create a Threadpthread_create()

Thread creation adds a new thread of controlto the current process.

The procedure main(), itself, is a singlethread of control.

Each thread executes simultaneously with allthe other threads within the calling process,and with other threads from other activeprocesses.


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Functions of pthread_create()

Creates the thread with passed

parameters

Stores thread ID upon success

Returns 0 on successful creation and a

non-zero value on failure; this propertycan be used for checking whether thethread has been at all created or not.


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The newly created thread :

shares all of the calling process' globaldata with the other threads in this process;however, it has its own set of attributesand private execution stack.

inherits the calling thread's signal mask,and scheduling priority. Pending signalsfor a new thread are not inherited and willbe empty.


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#include

int pthread_create(pthread_t * thread, pthread_attr_t * attr, void *(*start_routine)(void *), void * arg);

thread- address where the Thread Identification of the newlycreated thread is placed.

attr- address where the attributes the newly created thread shouldinherit. (if this argument is NULL, then the default attributes areinherited.)

start_routine- contains the function with which the new threadbegins execution. If start_routinereturns, the thread exits with the

exit status set to the value returned by start_routine.

arg- the argument passed to start_routine. Only one argument canbe passed. If more than one argument needs to be passed tostart_routine, the arguments can be packed into a structure and the

address of that structure can be passed to arg.


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Pitfall in pthread_create()

arg is a pointer to data, a commonmistake is to pass this parameter and

then overwritten it when calling a newthread.

You must make sure a thread will no

longer access this data beforeoverwriting it with a new value to bepassed to another thread.


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Get the Thread Identifier

pthread_self() - Gets the ID of the callingthread.

pthread_t pthread_self( void ); Yield Thread Execution

pthread_yield() - Causes the current

thread to yield its execution in favor ofanother thread with the same or greaterpriority.

void pthread_yield( void );


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WarningIf you create multiple threads, be careful

that there is no sharing of arguments, orthat sharing is safe:

For example: if you use same data structures for allthreads and modify its fields before each call tocreate pthread_create(). Some threads may not beable to read the arguments desired to them.

solution: use pthread_yield() after pthread_create() Safe way: have a separate arguments for each

threadhttp://navet.ics.hawaii.edu/~casanova/courses/ics432_fall08/slides/ics432_

pthreads.pdf


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Send a Signal to a Thread

pthread_kill() - sends a signal to a thread.

#include

#include

int kill( pid_t target, int sig);

int tkill( pid_t tid, int sig );


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kill() sends the signal sigto the thread specified by

target. targetmust be a process. The sigargumentmust be from the list given in signal.

tkill() sends the signal sigto the thread specified

by tid. tidmust be a thread within the sameprocess as the calling thread. The sigargumentmust be from the list given in signal. tkill() is Linuxspecific. Do not use tkill() if you plan on making

your program portable.


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Terminate a Thread

The thread returns from its start routine.

pthread_exit() - terminates a thread.

void pthread_exit( void *status);

The pthread_exit() function terminates the calling thread.All thread-specific data bindings are released.

If the calling thread is not detached, the thread's ID andthe exit status specified by statusare retained until thethread is waited for.

Otherwise, statusis ignored and the thread's ID can bereclaimed immediately.


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Wait for Thread Termination

pthread_join() - waits for a thread to terminate.

int pthread_join( pthread_t wait_for, void **status);

The pthread_join() function blocks the calling thread untilthe thread specified by wait_forterminates. Thespecified thread must be in the current process and mustnot be detached.

When statusis not NULL, it points to a location that isset to the exit status of the terminated thread whenpthread_join() returns successfully.


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pthread_join()

https://computing.llnl.gov/tutorials/pthreads/#Abstract


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Related Functions thr_sigsetmask() accesses the signal mask of the calling

thread

pthread_key_create(), thr_setspecific(), thr_getspecific() -

maintain thread-specific data

thr_getconcurrency(), thr_setconcurrency() - get and setthread concurrency level

(Concurrency: Many threads could be operating concurrently, on amulti threaded kernel.)

thr_getprio(), thr_setprio() - get and set thread priority


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Programming with

Synchronization use Mutex

For protecting critical areas of code


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Create a mutex

Initializes a static mutex with default attributes.

pthread_mutex_t mutex=PTHREAD_MUTEX_INITIALIZER

The PTHREAD_MUTEX_INITIALIZER macroinitializes the static mutex mutex, setting its

attributes to default values. This macro shouldonly be used for static mutexes, as no errorchecking is performed.


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Lock a mutex

pthread_mutex_lock()

int pthead_mutex_lock( pthread_mutex_t *mp);

Use pthead_mutex_lock() to lock the mutex pointed by mp. When themutex is already locked, the calling thread blocks until the mutexbecomes available (blocked threads wait on a prioritized queue). Whenpthread_mutex_lock() returns, the mutex is locked and the callingthread is the owner.


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pthread_mutex_t mutex1 =

PTHREAD_MUTEX_INITIALIZER;

if( condition holds){

pthread_mutex_lock( &mutex1 );{\\ CRITICAL SECTION}

pthread_mutex_unlock( &mutex1 );}


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Lock with a Nonblocking Mutex

int pthread_mutex_trylock( pthread_mutex_t*mp);

Use pthread_mutex_trylock() to attempt tolock the mutex pointed to by mp. Thisfunction is a non-blocking version ofpthread_mutex_lock(). When the mutex isalready locked, this call returns with anerror. Otherwise, the mutex is locked andthe calling thread is the owner.


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Unlock a Mutex

int pthread_mutex_unlock( pthread_mutex_t*mp);

Use the pthread_mutex_unlock() to unlockthe mutex pointed to by mp.

The mutex must be locked and the callingthread must be the one that last locked themutex (the owner).


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Related Functions

pthead_mutex_init() dynamically

initializes a mutual exclusion lock

pthread_mutex_destroy() - destroysmutex state


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Condition Variables

Use condition variables to atomically blockthreads until a particular condition is true.

Always use condition variables togetherwith a mutex lock.

pthread_mutex_lock();

while( condition_is_false )pthread_cond_wait();

pthread_mutex_unlock();


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Block on a Condition Variable

int pthread_cond_wait( pthread_cond_t *cvp,pthread_mutex_t *mp);

Use pthread_cond_wait() to atomically release the mutex

pointed by mpand to cause the calling thread to block

on the condition variable pointed to by cvp.

The blocked thread can be awakened by

pthread_cond_signal(), pthread_cond_broadcast(), or

when interrupted by delivery of a signal.


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Unblock a Specific Thread

int pthread_cond_signal( pthread_cond_t *cvp);

Use pthread_cond_signal() to unblock one threadthat is blocked on the condition variable pointed to

by cvp. Call pthread_cond_signal() under theprotection of the same mutex used with thecondition variable being signaled.

When no threads are blocked on the conditionvariable, the pthread_cond_signal() has no effect.


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Related Functions

pthread_cond_init() - initializes acondition variable

pthread_cond_timedwait() - blocks untila specified event

pthread_cond_broadcast() - unblocks all

threads pthread_cond_destroy() - destroys

condition variable state


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ASSIGNMENT 2

Mutual Exclusion

O S


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PROBLEM STATEMENTYour assignment is to create a banking system, withthreads that simulate the Sanders family accessing twoaccounts(checking and savings). The Sanders familyconsists of three people:

Bruce Sanders(the father), a freewheeling biker whois gone for long periods of time on drinking binges butwho also holds the patents on a large number of

devices like hooks, suction cups, and glass. Hespends a lot and makes a lot.

Jennifer Sanders(the mother), a home maker whodoesn't contribute anything but only takes a very smallamount at a time, she also keeps track of the finances

and makes sure there's enough money in the savingsaccount.

Jill Sanders(the daughter), who is away at collegeand therefore constantly drains financial resources.


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INPUT

The text file inputs are available on:http://web.mst.edu/~ercal/284/Asg-2/asg2-

father.txt,

http://web.mst.edu/~ercal/284/Asg-2/asg2-

mother.txthttp://web.mst.edu/~ercal/284/Asg-2/asg2-

daughter.txt

Each file describe the usage pattern of eachuser. Pattern of entry in input file are:

Character Account Amount

( example: d/w/t 0/1 50)
http://web.mst.edu/~ercal/284/Asg-2/asg2-father.txthttp://web.mst.edu/~ercal/284/Asg-2/asg2-father.txthttp://web.mst.edu/~ercal/284/Asg-2/asg2-mother.txthttp://web.mst.edu/~ercal/284/Asg-2/asg2-mother.txthttp://web.mst.edu/~ercal/284/Asg-2/asg2-daughter.txthttp://web.mst.edu/~ercal/284/Asg-2/asg2-daughter.txthttp://web.mst.edu/~ercal/284/Asg-2/asg2-daughter.txthttp://web.mst.edu/~ercal/284/Asg-2/asg2-daughter.txthttp://web.mst.edu/~ercal/284/Asg-2/asg2-daughter.txthttp://web.mst.edu/~ercal/284/Asg-2/asg2-daughter.txthttp://web.mst.edu/~ercal/284/Asg-2/asg2-daughter.txthttp://web.mst.edu/~ercal/284/Asg-2/asg2-mother.txthttp://web.mst.edu/~ercal/284/Asg-2/asg2-mother.txthttp://web.mst.edu/~ercal/284/Asg-2/asg2-mother.txthttp://web.mst.edu/~ercal/284/Asg-2/asg2-mother.txthttp://web.mst.edu/~ercal/284/Asg-2/asg2-mother.txthttp://web.mst.edu/~ercal/284/Asg-2/asg2-father.txthttp://web.mst.edu/~ercal/284/Asg-2/asg2-father.txthttp://web.mst.edu/~ercal/284/Asg-2/asg2-father.txthttp://web.mst.edu/~ercal/284/Asg-2/asg2-father.txthttp://web.mst.edu/~ercal/284/Asg-2/asg2-father.txt


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COMPONENTS OF THE

SOLUTION APPROACH1) TWO DIFFERENT ACCOUNTS CHECKINGAND SAVING (global variables)

2) MAIN FUNCTION

3) DIFFERENT THREADS FOR DIFFERENTUSERS4) START ROUTINE WHICH WILL SIMULATE THE

OPERATIONS TO BE DONE BY EACHTHREAD

5) THREE DIFFERENT OPERATIONS ON EACHACCOUNT (DEPOSIT, WITHDRAWAL,TRANSFER)

6) MUTEX LOCKS ON EACH ACCOUNT


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TWO DIFFERENT ACCOUNTSCHECKING AND SAVING

Denoted by two different notations

Two global variables to be protected

Needs two different mutex locks

Initial balance is zero

Three different operations on eachaccount is allowed


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MAIN FUNCTION

Create three threads usingpthread_create() to simulate father,

mother and daughter Join each thread using pthread_join() to

wait for each threads termination


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Passing Multiple Arguments

Each Thread has its id and file:

To pass the data like threadID, inputfile etc, a structure can be implemented holdingthreadID and corresponding inputfile.

FOR EXAMPLE-struct Eg{

mem1 (inputfile)mem2 number

};

Main()

{Eg THREADi;THREADi.inputfile = arg[i];THREADi.number = I;}

http://web.mst.edu/~ercal/284/ThreadExamples/passingthingstothreads.txt
http://web.mst.edu/~ercal/284/ThreadExamples/passingthingstothreads.txthttp://web.mst.edu/~ercal/284/ThreadExamples/passingthingstothreads.txt


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DIFFERENT THREADS FOR

DIFFERENT USERS pthread_create( &threadid, NULL, startroutine, (void

*)&THREADi)) )

startrountine function should read each file andperform actions encoded in the file

Use an error checking to see whether the thread iscreated or not.

[USE RETURN VALUE OF pthread_create()]

Join each thread using pthread_join() in main.


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START ROUTINE WHICH WILL SIMULATE THEOPERATIONS TO BE DONE BY EACH THREAD

Each THREADi is passed as parameter of start_routine().void *start_routine(void *userthread) // userthread : particular thread argument

or structure for each thread

Open (ifstream) input file

Read entire file into a string stream

Parse values from the string stream to variables while(!=EOF)

DO

{

operation first value of the entry (d/w/t)

account

second value of entry (checking/saving)amount third value of entry

CALL THE CORRESPONDING FUNCTION PASSING THE opeartion,account AND amount)

}

usleep(random amount of time) //put thread to execute in interleaved way


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MUTEX LOCKS ON EACHACCOUNT

For withdraw and deposit functions, theaccount being operated needs to be

locked by a mutex lock. For transfer function (between these two

accounts only), both the accounts need to

be locked by mutex locks.Pay attention toDeadlock: if one lock has been obtained ina thread other than transfer, then a

deadlock happens.

EXAMPLE


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EXAMPLE

DEPOSIT FUNCTION: ONLY ONE LOCK FOR CHECKING OR SAVING

if(account is CHECKING){

pthread_mutex_lock( &mutex_checking );\\ CRITICAL SECTIONINCREASE BALANCE IN ACCOUNT AND PRINT STATEMENT

pthread_mutex_unlock( &mutex_checking );

}else{

pthread_mutex_lock( &mutex_saving );\\ CRITICAL SECTIONINCREASE BALANCE IN ACCOUNT AND PRINT STATEMENT

pthread_mutex_unlock( &mutex_saving );}


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TRANSFER FUNCTION: TWO LOCKS FOR CHECKING AND SAVINGPAY ATTENTION TO THE ORDER OF LOCK AND UNLOCK OF TWO

ACCOUNTS

if(account is CHECKING){

pthread_mutex_lock( &mutex_checking );pthread_mutex_lock( &mutex_saving );

\\ CRITICAL SECTIONTRANSFER BALANCE BETWEEN CHECKING ACCOUNT AND

SAVING ACCOUNT AND PRINT STATEMENT

pthread_mutex_unlock( &mutex_saving );pthread_mutex_unlock( &mutex_checking );

}


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Withdraw / Overdraw logic

if(w from checking and wamount > checkingbalance)get money from savings to cover it (initiate atransfer)

if(w or t from saving and wamount > savingsbalanceand savingsbalance is +) allow balance to gonegative.

if(w or t from saving and savingsbalance is -) denyaction, print warning

if(t from checking and wamount > checkingbalanceand checkingbalance > 0) allow balance to gonegative, print warning.

if(t from checking and checkingbalance


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Useful Information

When the user deposits, withdraws, or transfers, weshould see a message to that effect. (e.g., "Brucedeposited x dollars. New balance total: y")

Compile command:

g++ assignment2.cppo assignment2lpthread

Run command:

assignment2 filename1 filename2 filename3

SAMPLE RUN


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SAMPLE RUN

Command: script mySession.txt, after running, exit

[cchv5f@dell12 assignment2]$./assignment2 father daughter motherJennifer:You do not have 37 dollars in checking to transfer.

Bruce:14 dollars deposited in savings. New Balance: 14Jill:Withdrawal of 30 failed. You only have 14 dollars available in savings.Jennifer:14 dollars has been transferred from savings to checking.Jennifer:You do not have 49 dollars in savings to transfer.Bruce:14 dollars deposited in checking. New balance: 28Bruce:32 dollars deposited in checking. New balance: 60Jill:Withdrawal of 13 successful. 47 dollars remain in your checking

account.User 2:33 dollars has been transferred from checking tosavings.

Jill:Withdrawal of 5 successful. 28 dollars remain in your savings account.

Jennifer:10 dollars has been transferred from checking to savings.


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Questions?

THANK YOU

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Asg2 Thread Supp