Revision of rws.c

psbhatnagar revised this gist 1 week ago. Go to revision

1 file changed, 79 insertions

rws.c(file created)

		@@ -0,0 +1,79 @@
1	+	#include <pthread.h>
2	+	#include <semaphore.h>
3	+	#include <stdio.h>
4	+
5	+	/*
6	+	This program provides a possible solution for the first readers-writers problem
7	+	using a mutex and a semaphore.
8	+
9	+	10 readers and 5 writers are used to demonstrate the solution. Feel free to
10	+	change these values.
11	+	*/
12	+
13	+	sem_t wrt;
14	+	pthread_mutex_t mutex;
15	+	int cnt = 1;
16	+	int numreader = 0;
17	+
18	+	void writer(void wno)
19	+	{
20	+	sem_wait(&wrt);
21	+	cnt = cnt * 2;
22	+	printf("Writer %d modified cnt to %d\n", ((int )wno), cnt);
23	+	sem_post(&wrt);
24	+	return NULL;
25	+	}
26	+
27	+	void reader(void rno)
28	+	{
29	+	// Reader acquires the lock before modifying numreader
30	+	pthread_mutex_lock(&mutex);
31	+	numreader++;
32	+	if (numreader == 1) {
33	+	sem_wait(&wrt); // If this is the first reader, it blocks the writer
34	+	}
35	+	pthread_mutex_unlock(&mutex);
36	+
37	+	// Reading section
38	+	printf("Reader %d: read cnt as %d\n", ((int )rno), cnt);
39	+
40	+	// Reader acquires the lock before modifying numreader
41	+	pthread_mutex_lock(&mutex);
42	+	numreader--;
43	+	if (numreader == 0) {
44	+	sem_post(&wrt); // If this is the last reader, it wakes up the writer
45	+	}
46	+	pthread_mutex_unlock(&mutex);
47	+
48	+	return NULL;
49	+	}
50	+
51	+	int main()
52	+	{
53	+	pthread_t read_t[10], write_t[5];
54	+	pthread_mutex_init(&mutex, NULL);
55	+	sem_init(&wrt, 0, 1);
56	+
57	+	int a[10] = {1,2,3,4,5,6,7,8,9,10}; // Just used for numbering readers/writers
58	+
59	+	for (int i = 0; i < 10; i++) {
60	+	pthread_create(&read_t[i], NULL, reader, (void *)&a[i]);
61	+	}
62	+
63	+	for (int i = 0; i < 5; i++) {
64	+	pthread_create(&write_t[i], NULL, writer, (void *)&a[i]);
65	+	}
66	+
67	+	for (int i = 0; i < 10; i++) {
68	+	pthread_join(read_t[i], NULL);
69	+	}
70	+
71	+	for (int i = 0; i < 5; i++) {
72	+	pthread_join(write_t[i], NULL);
73	+	}
74	+
75	+	pthread_mutex_destroy(&mutex);
76	+	sem_destroy(&wrt);
77	+
78	+	return 0;
79	+	}

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