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proj-4.c
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proj-4.c
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#include "sem.h"
#define READER 5
#define WRITER 2
TCB_t *runQ = 0;
SEM_t *mutex = 0, *rsem = 0, *wsem = 0;
int rwc = 0, rc = 0, wwc = 0, wc = 0, shared_int = 0;
int readercount=0;
void reader();
void reader_entry();
void reader_exit();
void writer();
void writer_entry();
void writer_exit();
void main(char** args) {
TCB_t* threads[READER + WRITER];
puts("initializing semaphores and threads");
srand(time(NULL));
mutex = malloc(sizeof(SEM_t));
rsem = malloc(sizeof(SEM_t));
wsem = malloc(sizeof(SEM_t));
InitSem(mutex, 1);
InitSem(rsem, 0);
InitSem(wsem, 0);
InitQueue(&runQ);
int i = 0, j = 0, h = 0;
while (i < READER + WRITER) {
int r = rand() % 2;
if (j < READER && r == 0) {
puts("Adding reader");
start_thread(threads[i], reader);
i++; j++;
}
if (h < WRITER && r == 1) {
puts("Adding writer");
start_thread(threads[i], writer);
i++; h++;
}
}
puts("runQ content:");
printQueue(runQ);
puts("\nstarting threads\n");
run();
}
void reader() {
readercount ++;
while (1 > 0) {
//printf("Reader[%p]: Start\n", runQ);
reader_entry();
//printf("Reader[%p]: Entered\n", runQ);
P(mutex);
printf("Reader %d reading from writer : %d\n",readercount,runQ, shared_int);
sleep(1);
V(mutex);
//printf("Reader[%p]: Exiting\n", runQ);
reader_exit();
//printf("Reader[%p]: Exit\n", runQ);
}
}
void reader_entry() {
P(mutex);
if (wwc > 0 || wc > 0) {
rwc++;
V(mutex);
//printf("Reader[%p]: Adding to wait queue\n", runQ);
//printf("\t(wwc:%d, wc:%d, rwc:%d, rc:%d)\n", wwc, wc, rwc, rc);
P(rsem);
rwc--;
//printf("Reader[%p]: Returned from wait queue\n", runQ);
//printf("\t(wwc:%d, wc:%d, rwc:%d, rc:%d)\n", wwc, wc, rwc, rc);
}
rc++;
if (rwc > 0) {
//printf("Reader[%p]: Releasing a reader\n", runQ);
//printf("\t(wwc:%d, wc:%d, rwc:%d, rc:%d)\n", wwc, wc, rwc, rc);
V(rsem);
} else {
V(mutex);
}
}
void reader_exit() {
P(mutex);
rc--;
if (rc == 0 && wwc > 0) {
//printf("Reader[%p]: Releasing a writer\n", runQ);
//printf("\t(wwc:%d, wc:%d, rwc:%d, rc:%d)\n", wwc, wc, rwc, rc);
V(wsem);
} else {
V(mutex);
}
}
void writer() {
while (1 > 0) {
int wrc =0;
//printf("Writer[%p]: Start\n", runQ);
writer_entry();
//printf("Writer[%p]: Entered\n", runQ);
P(mutex);
shared_int = 2;
printf("Writer %d: %d\n", wrc++, shared_int);
sleep(1);
V(mutex);
//printf("Writer[%p]: Exiting\n", runQ);
if (wrc>2){
wrc=0;}
writer_exit();
//printf("Writer[%p]: Exit\n", runQ);
}
}
void writer_entry() {
P(mutex);
if (rc > 0 || wc > 0) {
wwc++;
V(mutex);
P(wsem);
wwc--;
}
wc++;
V(mutex);
}
void writer_exit() {
P(mutex);
wc--;
if (rwc > 0) {
//printf("Writer[%p]: Releasing a reader\n", runQ);
//printf("\t(wwc:%d, wc:%d, rwc:%d, rc:%d)\n", wwc, wc, rwc, rc);
V(rsem);
}
else if (wwc > 0) {
//printf("Writer[%p]: Releasing a writer\n", runQ);
//printf("\t(wwc:%d, wc:%d, rwc:%d, rc:%d)\n", wwc, wc, rwc, rc);
V(wsem);
}
}