stuff

Examples/ipc/ipcmsg1.c

@@ -0,0 +1,71 @@
+/*
+ * ipcmsg1.c - Using a message queue to send data from 
+ *             a parent process to a child process
+ *             NOTE: message queues are persistent
+ */
+
+#include <sys/types.h> // needed for pid_t
+#include <sys/wait.h>  // needed for wait system call
+#include <unistd.h>    // needed for fork system call
+#include <stdlib.h>    // needed for exit
+#include <stdio.h>     // needed for printf, perror
+#include <mqueue.h>    // needed for mq system calls
+#include <string.h>    // needed for strcpy
+
+/* Struct for the queue message */
+typedef struct message {
+    int message_id;
+    char string[10];
+} message;
+
+int main()
+{
+    // Create attributes for new queue
+    struct mq_attr queue_attr;
+    queue_attr.mq_flags = 0;    // Ignored by kernel
+    queue_attr.mq_maxmsg = 10;  // Max messages the queue supports
+    queue_attr.mq_msgsize = sizeof(message);
+    queue_attr.mq_curmsgs = 0;  // Not used
+
+    // Create and open a queue
+    mqd_t mqdes = mq_open("/CS3841QUEUE", O_RDWR | O_CREAT, S_IRUSR | S_IWUSR, &queue_attr);
+    if(mqdes == -1) {
+        printf("COULD NOT OPEN QUEUE\n");
+        exit(EXIT_FAILURE);
+    }
+
+    pid_t pid = fork(); // fork into 2 processes
+
+    if(pid < 0) // error
+    {
+        perror("fork");
+        exit(EXIT_FAILURE);
+    }
+    else if(pid == 0) // child
+    {
+        // Child receives message from parent
+        message from_parent;
+        mq_receive(mqdes, (char*)&from_parent, sizeof(message), NULL);
+        printf("Child got %d: %s from parent\n", from_parent.message_id, from_parent.string);
+
+        // Close the queue
+        mq_close(mqdes);
+
+        return 0; // Return success
+    }
+    else // parent
+    {
+        // Parent sends message to child
+        message to_child;
+        to_child.message_id = 10;
+        strcpy(to_child.string, "HELLO");
+        mq_send(mqdes, (char*)&to_child, sizeof(message), 0);
+
+        // Wait for child
+        wait(0);
+
+        // Close the queue
+        mq_close(mqdes);
+    }
+    return 0; // Return success
+}