SOURCE FILE: star.cpp
/*
------------5-----------------
--------1-------2-------------
----8-------0-------6---------
--------4-------3-------------
------------7-----------------
*/
/* Star Formation Program */
#include <iostream>
#include <sched.h>
#include <time.h>
#include <pthread.h>
#include "sem.h"
#define THREAD_COUNT 9
using namespace std;
extern sim_semaphore create_sim_sem(int) ;
extern void wait_sem (sim_semaphore) ;
extern void signal_sem (sim_semaphore) ;
/* For technical reasons, we use the pthread mutex below,
instead of a semaphore, to lock the screen for output. Don't
change this. */
pthread_mutex_t stdoutLock ;
/* Here declare whatever shared variables you need for
synchronization. Variables declared here will be visible
to (shared by) all the threads in the task. */
/* HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH */
/* HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH */
/* These are global variable to represent threads created
dynamically. */
pthread_t thr[THREAD_COUNT] ;
/* This is included to facilitate adding random delays in the code
-- as a debugging aid. */
extern long random(void);
/* This can be changed to 1, but the resulting diagnostic output
will probably seem excessive. */
int checking = 0 ;
/* A data type - a struct (class) with an int field to represent
a thread ID. */
struct threadIdType
{
int id ;
};
/* ################################################## */
/* init */
/* ################################################## */
void init()
{
/* This code initializes special mutex lock for screen output.
Just leave this alone. */
if ( 0!=pthread_mutex_init(&stdoutLock, NULL) )
{ cout << "MUTEX INITIALIZATION FAILURE!" << endl ;
exit(-1) ;}
/* Here insert the code that you want to intialize
the shared variables that you are using
for synchronization. */
/* HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH */
/* HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH */
/* This initializes a random number generator */
srandom(time((time_t *) 0));
}
/* ################################################## */
/* rand_delay */
/* ################################################## */
void rand_delay(int max)
{
int m_delay, j ;
m_delay = (int) random()%max ;
for (j=0; j<m_delay; j++) sched_yield();
}
/* ################################################## */
/* childMessage */
/* ################################################## */
void childMessage (int ID)
{
pthread_mutex_lock(&stdoutLock) ;
cout << "Child # " << ID
<< " is now in position.\n" ;
pthread_mutex_unlock(&stdoutLock) ;
}
/* ################################################## */
/* child */
/* ################################################## */
void * child(void * idPtr)
{
/* This is just a change of data type for convenience. Now
'me' is the number of the child. Children have numbers from
0 to 8. */
int me = ((threadIdType *) (idPtr))->id, temp ;
/* Delay code inserted here to magnify the chances that child
threads will delay each other. The student
completing the program should think of more ways to insert
random delays that are likely to 'stress test' the program. */
rand_delay(100) ;
/* Here put whatever synchronization code is required prior
to the code where the child process declares that it has
put itself into position. */
/* HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH */
/* HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH */
childMessage(me) ; // The child declares that it is in position
/* Here put whatever synchronization code is required AFTER
the code where the child process declares that it has
put itself into position. */
/* HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH */
/* HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH */
pthread_exit ((void *)0) ;
}
/* ################################################## */
/* mother */
/* ################################################## */
/* The mother spawns child threads and then waits for
them all to finish. The mother's waiting has to be
implemented as part of the overall protocol - using
the sim_semaphore data type. */
void mother()
{
int i;
/* This is a pointer to a struct (class) that contains an int
field - it is a convenient data type to use as the parameter
to the child function. */
threadIdType * idPtr ;
/* Create child threads numbered 1 through 8. */
pthread_mutex_lock(&stdoutLock) ;
cout << "Mother Begins Spawning Threads.\n" << endl ;
pthread_mutex_unlock(&stdoutLock) ;
for (i = 0; i < THREAD_COUNT ; i++)
{
idPtr = new threadIdType ; /* allocate memory for struct */
idPtr->id = i ; /* records current index as the child's ID */
/* The call below is what actually creates the child thread
and passes a pointer to the struct 'idPtr' as the
parameter to the child function. */
if ( 0!=pthread_create(&thr[i], NULL, child, (void *) idPtr) )
{ pthread_mutex_lock(&stdoutLock) ; /* 'error out' code here */
cout << "THREAD CREATION FAILURE!" << endl ;
pthread_mutex_unlock(&stdoutLock) ;
exit(-1) ; }
/* The call to pthread_detach() below marks a child
thread as 'detached' so that the system will not
expect the parent to 'join' (wait for) it. */
if (0!=pthread_detach(thr[i]))
{ pthread_mutex_lock(&stdoutLock) ;/* 'error out' code here */
cout << "THREAD DETACHMENT FAILURE!" << endl ;
pthread_mutex_unlock(&stdoutLock) ;
exit(-1) ;}
}
pthread_mutex_lock(&stdoutLock) ;
cout << "Mother Finishes Spawning Threads.\n" << endl ;
pthread_mutex_unlock(&stdoutLock) ;
/* Some synchronization code is needed here to make the mother
behave correctly - she is not supposed to exit until after
all the children have finished putting themselves into position. */
/* HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH */
/* HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH */
/*
REMOVE THE DELAY CODE BELOW AFTER YOU FINISH
ADDING SYNCHRONIZATION CODE TO THE PROGRAM.
The delay below is an artificial elment of the program.
When the program runs un-synched and without the delay
below, it's likely that the mother will exit before most
or all of the child threads get a chance to do anything
at all. With the delay below in place, in many runs of
the un-synched program, some or all of the children will
have time to write their messages to the screen, which
will allow the student to see how the un-synched
child threads behave.
Once the student has added sufficient synchronization code,
the program should execute correctly in every run, WITHOUT
delay below in the program any more.
It is important for the student to take it out eventually,
to make sure that the program can execute correctly without it. */
rand_delay(1000) ; /* REMOVE THIS DELAY BEFORE FINAL TESTING */
pthread_mutex_lock(&stdoutLock) ;
cout << "\nAll children are now in position.\n" ;
cout << "Mother exiting ... \n\n" ;
pthread_mutex_unlock(&stdoutLock) ;
return ;
}
/* ################################################## */
/* main */
/* ################################################## */
int main()
{
cout << "\nWelcome to The Star Chamber!\n\n" ;
/* This calls the function that performs initializations. */
init();
/* Execute the mother() function */
mother();
return 0 ;
}