Message Queue

Message Queue/receiver.c

@@ -0,0 +1,68 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/select.h>
+#include <unistd.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <mqueue.h>
+#include <errno.h>
+
+#define MAX_MESSAGES 10
+#define MAX_MSG_SIZE 256
+#define MSG_BUFFER_SIZE (MAX_MSG_SIZE + 10)
+#define QUEUE_PERMISSION 0660
+
+int
+main(int argc, char** argv) {
+
+	fd_set readfds;
+	char buffer[MSG_BUFFER_SIZE];
+	int msgq_fd = 0;
+
+	if (argc <= 1) {
+		printf("provide a receipient msgQ name : format </msgq-name>\n");
+		return 0;
+	}
+
+	/* To set msgQ attributes */
+	struct mq_attr attr;
+	attr.mq_flags = 0;
+	attr.mq_maxmsg = MAX_MESSAGES;
+	attr.mq_msgsize = MAX_MSG_SIZE;
+	attr.mq_curmsgs = 0;
+
+	if ((msgq_fd = mq_open(argv[1], O_RDONLY | O_CREAT , QUEUE_PERMISSION, &attr)) == -1) {
+		printf("Client : mq_open failed, errno = %d", errno);
+		exit(1);
+	}
+
+	while (1) {
+
+		/* Empty the fd_set data structure. */
+		FD_ZERO(&readfds);
+
+		/* Insert MsgQ fd to fd_set. */
+		FD_SET( msgq_fd, &readfds);
+		printf("Receiver blocked on select()....\n");
+
+		/* Use select system call to detect the data enqueue for message queue. */
+		select(msgq_fd + 1, &readfds, NULL, NULL, NULL);
+
+		if (FD_ISSET(msgq_fd, &readfds)) {
+			printf("Msg recvd msgQ %s\n", argv[1]);
+
+			memset(buffer, 0, MSG_BUFFER_SIZE);
+
+			/* Read the data from message queue. */
+			if (mq_receive(msgq_fd, buffer, MSG_BUFFER_SIZE, NULL) == -1) {
+				printf("mq_receive error, errno = %d\n", errno);
+				exit(1);
+			}
+			printf("Msg received from Queue = %s\n", buffer);
+		}
+	}
+
+	return 0;
+}