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

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

Screenshots of output

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; } } }