Program Multithreaded Reader Writers Using Semaphores in C

Instructions

Objective

If you're seeking assistance with a C assignment, I can provide guidance on tackling the task. One such assignment involves writing a C program for implementing a multithreaded reader-writer solution using semaphores and the test-and-set mechanism. This program would aim to manage concurrent access to shared resources while maintaining data integrity. By carefully coordinating reader and writer threads through semaphores and utilizing the test-and-set operation to handle critical sections, the program can ensure proper synchronization.

Requirements and Specifications

multithreaded reader writers using semaphores and test and set using C++

Screenshots of output

multithreaded reader writers using semaphores and test and set using C++ 1

multithreaded reader writers using semaphores and test and set using C++ 2

Source Code

SEAMAPHORES

#include 
#include 
#include 
int currentproc;
// program counters
int r_pc[3] = {0, 0, 0};
int w_pc[3] = {0, 0};
// semaphores
typedef struct sem
{
 int val;
 int waiting[5];
 int nwaiting;
}semaphore;
semaphore mutex = {1, {0}, 0}; // reader shared mutex
semaphore rsem = {2, {0}, 0}; // semaphore for readers
semaphore wsem = {1, {0}, 0}; // semaphore for writers
// counters
int AR = 0; // active readers
int critical_readers = 0;
int critical_writers = 0;
// panic flag
int panic = 0;
int wait(semaphore *sem)
{
 if (sem->val == 0)
 {
 for (int i = 0; i < sem->nwaiting; i++)
 if (sem->waiting[i] == currentproc)
 return 0;
 sem->waiting[sem->nwaiting++] = currentproc;
 return 0;
 }
 else
 {
 sem->val--;
 return 1;
 }
 }
void signal(semaphore *sem)
 {
 if (sem->nwaiting > 0)
 {
 switch (sem->waiting[0])
 {
 case 0: r_pc[0]++; break;
 case 1: r_pc[1]++; break;
 case 2: r_pc[2]++; break;
 case 3: w_pc[0]++; break;
 case 4: w_pc[1]++; break;
 }
 sem->nwaiting--;
 for (int i = 0; i < sem->nwaiting; i++)
 sem->waiting[i] = sem->waiting[i + 1];
 }
 else
 {
 sem->val++;
 }
 }
// Reader
void r(int n)
 {
 switch(r_pc[n]) // select instruction position
 {
 case 0: // try to enter critical section start for readers
 if (wait(&mutex)) // wait for mutex
 r_pc[n]++; // advance to next instruction;
 break;
 case 1:
 AR++; // one more reader
 r_pc[n]++; // advance to instruction
 break;
 case 2:
 if (AR == 1) // if first reader
 {
 r_pc[n]++; // advance to next instruction;
 }
 else
 r_pc[n] += 2; // advance to instruction
 break;
 case 3:
 if (wait(&wsem)) // wait if writer active
 r_pc[n]++;
 break;
 case 4: // free mutex
 signal(&mutex); // unlock mutex
 r_pc[n]++; // advance to next instruction;
 break;
 case 5:
 if (wait(&rsem)) // wait if readers active
 r_pc[n]++;
 break;
 case 6:
 critical_readers++;
 r_pc[n]++; // advance to next instruction;
 break;
 case 7:
 if (critical_readers > 2 || critical_writers > 0) // if conditions are not met
 panic = 1; // panic
 printf("Reader %d in critical section [readers=%d, writers=%d]\n", n, critical_readers, critical_writers);
 r_pc[n]++; // advance to next instruction;
 break;
 case 8:
 critical_readers--;
 r_pc[n]++; // advance to next instruction;
 break;
 case 9: // free reader
 signal(&rsem); // unlock reader
 printf("Reader process %d out of critical section...\n", n);
 r_pc[n]++; // advance to next instruction;
 break;
 case 10: // leave critical section
 if (wait(&mutex)) // wait for mutex
 r_pc[n]++; // advance to next instruction;
 break;
 case 11:
 AR--; // one less active reader
 r_pc[n]++; // advance to instruction
 break;
 case 12:
 if (AR == 0)
 {
 r_pc[n]++; // advance to next instruction;
 }
 else
 r_pc[n] += 2; // advance to instruction 14
 break;
 case 13:
 signal(&wsem); // ok to write
 r_pc[n]++; // advance to next instruction;
 break;
 case 14: // free mutex
 signal(&mutex); // unlock mutex
 r_pc[n]++; // advance to next instruction;
 break;
 case 15:
 r_pc[n] = 0; // cycle
 break;
 }
 }
// Writer
void w(int n)
 {
 switch(w_pc[n]) // select instruction position
 {
 case 0: // try to enter critical section start for writers
 if (wait(&wsem)) // wait for semaphore
 w_pc[n]++; // advance to next instruction;
 break;
 case 1:
 critical_writers++;
 w_pc[n]++; // advance to next instruction;
 break;
 case 2:
 if (critical_readers > 0 || critical_writers > 1) // if conditions are not met
 panic = 1; // panic
 printf("Writer %d in critical section [readers=%d, writers=%d]\n", n, critical_readers, critical_writers);
 w_pc[n]++; // advance to next instruction;
 break;
 case 3:
 critical_writers--;
 w_pc[n]++; // advance to next instruction;
 break;
 case 4:
 signal(&wsem); // ok to write
 printf("Writer process %d out of critical section...\n", n);
 w_pc[n]++; // advance to next instruction;
 break;
 case 5:
 w_pc[n] = 0; // cycle
 break;
 }
 }
int main()
 {
 srand(time(NULL)); // initialize random generator seed to current time
 for (int i = 0; i < 10000; i++)
 {
 int cointoss = rand() % 5;
 currentproc = cointoss;
 switch (cointoss)
 {
 case 0: r(0); break;
 case 1: r(1); break;
 case 2: r(2); break;
 case 3: w(0); break;
 case 4: w(1); break;
 }
 if (panic)
 {
 printf("Invalid number of writers or readers in critical section!!\n");
 printf("Terminating program...\n");
 break;
 }
 }
 }

TEST AND SET

#include 
#include 
#include 
// program counters
int r_pc[3] = {0, 0, 0};
int w_pc[3] = {0, 0};
// locks
int lock = 0; // reader shared lock
int rlock = 0; // lock for readers
int wlock = 0; // lock for writers
// counters
int AR = 0; // active readers
int critical_readers = 0;
int critical_writers = 0;
// panic flag
int panic = 0;
int testandset(int *lock)
{
 if (*lock == 1)
 return 1; // failure
 else
 {
 *lock = 1;
 return 0; // success
 }
 }
// Reader
void r(int n)
 {
 switch(r_pc[n]) // select instruction position
 {
 case 0: // try to enter critical section start for readers
 if (!testandset(&lock)) // wait for lock
 r_pc[n]++; // advance to next instruction;
 break;
 case 1:
 AR++; // one more reader
 r_pc[n]++; // advance to instruction
 break;
 case 2:
 if (AR == 1) // if first reader
 {
 r_pc[n]++; // advance to next instruction;
 }
 else
 r_pc[n] += 2; // advance to instruction
 break;
 case 3:
 if (!testandset(&wlock)) // wait if writer active
 r_pc[n]++;
 break;
 case 4: // free readers lock
 lock = 0; // unlock
 r_pc[n]++; // advance to next instruction;
 break;
 case 5:
 if (AR <= 2) // wait if readers active
 r_pc[n]++;
 break;
 case 6:
 critical_readers++;
 r_pc[n]++; // advance to next instruction;
 break;
 case 7:
 if (critical_readers > 2 || critical_writers > 0) // if conditions are not met
 panic = 1; // panic
 printf("Reader %d in critical section [readers=%d, writers=%d]\n", n, critical_readers, critical_writers);
 r_pc[n]++; // advance to next instruction;
 break;
 case 8:
 critical_readers--;
 r_pc[n]++; // advance to next instruction;
 break;
 case 9: // free reader
 printf("Reader process %d out of critical section...\n", n);
 r_pc[n]++; // advance to next instruction;
 break;
 case 10: // leave critical section
 if (!testandset(&lock)) // wait for mutex
 r_pc[n]++; // advance to next instruction;
 break;
 case 11:
 AR--; // one less active reader
 r_pc[n]++; // advance to instruction
 break;
 case 12:
 if (AR == 0)
 {
 r_pc[n]++; // advance to next instruction;
 }
 else
 r_pc[n] += 2; // advance to instruction
 break;
 case 13:
 wlock = 0; // ok to write
 r_pc[n]++; // advance to next instruction;
 break;
 case 14: // free lock
 lock = 0; // unlock
 r_pc[n]++; // advance to next instruction;
 break;
 case 15:
 r_pc[n] = 0; // cycle
 break;
 }
 }
// Writer
void w(int n)
 {
 switch(w_pc[n]) // select instruction position
 {
 case 0: // try to enter critical section start for writers
 if (!testandset(&wlock)) // wait for semaphore
 w_pc[n]++; // advance to next instruction;
 break;
 case 1:
 critical_writers++;
 w_pc[n]++; // advance to next instruction;
 break;
 case 2:
 if (critical_readers > 0 || critical_writers > 1) // if conditions are not met
 panic = 1; // panic
 printf("Writer %d in critical section [readers=%d, writers=%d]\n", n, critical_readers, critical_writers);
 w_pc[n]++; // advance to next instruction;
 break;
 case 3:
 critical_writers--;
 w_pc[n]++; // advance to next instruction;
 break;
 case 4:
 wlock = 0; // ok to write
 printf("Writer process %d out of critical section...\n", n);
 w_pc[n]++; // advance to next instruction;
 break;
 case 5:
 w_pc[n] = 0; // cycle
 break;
 }
 }
int main()
 {
 srand(time(NULL)); // initialize random generator seed to current time
 for (int i = 0; i < 10000; i++)
 {
 int cointoss = rand() % 5;
 switch (cointoss)
 {
 case 0: r(0); break;
 case 1: r(1); break;
 case 2: r(2); break;
 case 3: w(0); break;
 case 4: w(1); break;
 }
 if (panic)
 {
 printf("Invalid number of writers or readers in critical section!!\n");
 printf("Terminating program...\n");
 break;
 }
 }
 }

Multithreaded Reader Writers Using Semaphores and Test and Set in C Language Assignment Solution.

Instructions

Requirements and Specifications