CS3871/assignments/sync: Added basic semaphore solution (no concurent readers)

	P(sem)
	  crit
	V(sem)

Removed debugging prints

1 files changed, 19 insertions, 7 deletions

diff --git a/sync/writer.c b/sync/writer.c
index b1ab9ed..d38dd70 100644
--- a/sync/writer.c
+++ b/sync/writer.c
@@ -4,12 +4,15 @@
 #include <stdlib.h>
 #include <sys/ipc.h>
 #include <sys/select.h>
+#include <sys/sem.h>
 #include <sys/shm.h>
 #include <sys/types.h>
 #include <sys/types.h>
 #include <time.h>
 #include <unistd.h>
 
+#define NSEM 3
+
 char *mem;
 
 void quit(signum)
@@ -23,9 +26,9 @@ int main(argc, argv)
 int argc;
 char **argv;
 {
-printf("\tW STARTING\n");
-	int shmid, i, pid, id;
+	int shmid, semid, i, pid, id;
 	char *mem;
+	struct sembuf sb;
 
 	if (argc < 2) {
 		printf("usage: writer [id]\n");
@@ -34,7 +37,6 @@ printf("\tW STARTING\n");
 
 	id = atoi(argv[1]);
 
-printf("\tW%d. started...\n", id);
 
 	if ((shmid = shmget(52, 1<<14, IPC_CREAT | 0666)) == -1){
 		perror("shmget: shmget failed");
@@ -45,20 +47,30 @@ printf("\tW%d. started...\n", id);
 		perror("shmat");
 		exit(1);
 	}
+printf("Wshmid: %x\n", shmid);
+
+	if ((semid = semget(shmid, NSEM, 0)) == -1) {
+		perror("Wsemget: ");
+		exit(1);
+	}
 
 	signal(SIGQUIT, quit);
-printf("\tW%d. SHMID: %d\n", id, shmid);
 	
 	srand(time(NULL));
 
 	while (1) {
-printf("\tW%d. testing...\n", id);
 		rand() % id;
-printf("\tW%d. writing...\n", id);
+		
+		sb.sem_num = 0; sb.sem_op = -1; sb.sem_flg = 0;
+		semop(semid, &sb, 1);
+
 		for (i = 0; i < 1<<14; i++) {
 			mem[i]= 0x30 + id;
 		}
-printf("\tW%d. waiting...\n");
+		
+		sb.sem_op = 1;
+		semop(semid, &sb, 1);
+
 		sleep(rand() % ((id * 2) + 1));
 	}
 }