reader writer lock + small cleanups

threads-sema/rwlock.c

@@ -0,0 +1,94 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <pthread.h>
+#include <semaphore.h>
+#include <unistd.h>
+
+#include "common.h"
+#include "common_threads.h"
+
+typedef struct _rwlock_t {
+    sem_t writelock;
+    sem_t lock;
+    int readers;
+} rwlock_t;
+
+void rwlock_init(rwlock_t *lock) {
+    lock->readers = 0;
+    Sem_init(&lock->lock, 1); 
+    Sem_init(&lock->writelock, 1); 
+}
+
+void rwlock_acquire_readlock(rwlock_t *lock) {
+    Sem_wait(&lock->lock);
+    lock->readers++;
+    if (lock->readers == 1)
+	Sem_wait(&lock->writelock);
+    Sem_post(&lock->lock);
+}
+
+void rwlock_release_readlock(rwlock_t *lock) {
+    Sem_wait(&lock->lock);
+    lock->readers--;
+    if (lock->readers == 0)
+	Sem_post(&lock->writelock);
+    Sem_post(&lock->lock);
+}
+
+void rwlock_acquire_writelock(rwlock_t *lock) {
+    Sem_wait(&lock->writelock);
+}
+
+void rwlock_release_writelock(rwlock_t *lock) {
+    Sem_post(&lock->writelock);
+}
+
+int read_loops;
+int write_loops;
+int counter = 0;
+
+rwlock_t mutex;
+
+void *reader(void *arg) {
+    int i;
+    int local = 0;
+    for (i = 0; i < read_loops; i++) {
+	rwlock_acquire_readlock(&mutex);
+	local = counter;
+	rwlock_release_readlock(&mutex);
+	printf("read %d\n", local);
+    }
+    printf("read done: %d\n", local);
+    return NULL;
+}
+
+void *writer(void *arg) {
+    int i;
+    for (i = 0; i < write_loops; i++) {
+	rwlock_acquire_writelock(&mutex);
+	counter++;
+	rwlock_release_writelock(&mutex);
+    }
+    printf("write done\n");
+    return NULL;
+}
+
+int main(int argc, char *argv[]) {
+    if (argc != 3) {
+	fprintf(stderr, "usage: rwlock readloops writeloops\n");
+	exit(1);
+    }
+    read_loops = atoi(argv[1]);
+    write_loops = atoi(argv[2]);
+    
+    rwlock_init(&mutex); 
+    pthread_t c1, c2;
+    Pthread_create(&c1, NULL, reader, NULL);
+    Pthread_create(&c2, NULL, writer, NULL);
+    Pthread_join(c1, NULL);
+    Pthread_join(c2, NULL);
+    printf("all done\n");
+    return 0;
+}
+    
+