Processes by Kevin Brack

.gitignore

@@ -1 +1,3 @@
 .DS_Store
+examples
+a.out

ex1/ex1.c

@@ -8,7 +8,48 @@
 
 int main(void)
 {
-    // Your code here
+    printf("BEFORE FORK (pid: %d) \n", (int)getpid());
+    int x = 10;
+    int *xp = &x;
+
+    int f = fork();
+    if (f < 0)
+    {
+        printf("%s\n", "Fork faliled");
+        exit(1);
+    }
+    else if (f == 0)
+    {
+        // we are in the child branch
+        printf("Greetings from child (pid: %d)\n", f);
+        printf("Childs x: %i\n", x);
+        printf("Childs pointer to x: %p\n", xp);
+        printf("Childs pointer to x value: %i\n", *xp);
+        x = x + 5;
+        printf("%s\n", "Child adding 5 to x");
+        printf("Childs x: %i\n", x);
+        printf("Childs pointer to x: %p\n", xp);
+        printf("Childs pointer to x value: %i\n", *xp);
+        int *npx = &x;
+        printf("Childs NEW pointer to x: %p\n", npx);
+        printf("%s\n", "---END CHILD---\n\n");
+    }
+    else
+    {
+        // we are in the parent branch
+        printf("Greetings from parent (pid: %d)\n", f);
+        printf("Parents x: %i\n", x);
+        printf("Parents pointer to x: %p\n", xp);
+        printf("Parents pointer to x value: %i\n", *xp);
+        x = x + 5;
+        printf("%s\n", "Parent adding 5 to x");
+        printf("Parents x: %i\n", x);
+        printf("Parents pointer to x: %p\n", xp);
+        printf("Parents pointer to x value: %i\n", *xp);
+        int *npx = &x;
+        printf("Childs NEW pointer to x: %p\n", npx);
+        printf("%s\n", "---END PARENT---\n\n");
+    }
 
     return 0;
 }

ex2/ex2.c

@@ -1,5 +1,5 @@
-// Write a program that opens the text.txt file (with the `fopen()` library call) located in this directory 
-// and then calls `fork()` to create a new process. Can both the child and parent access the file descriptor 
+// Write a program that opens the text.txt file (with the `fopen()` library call) located in this directory
+// and then calls `fork()` to create a new process. Can both the child and parent access the file descriptor
 // returned by `fopen()`? What happens when they are written to the file concurrently?
 
 #include <stdio.h>
@@ -8,7 +8,28 @@
 
 int main(void)
 {
-    // Your code here 
-
+    FILE *fp;
+    fp = fopen("text.txt", "r+");
+    int f = fork();
+    if (f < 0)
+    {
+        printf("%s\n", "Fork faliled");
+        exit(1);
+    }
+    else if (f == 0)
+    {
+        // we are in the child branch
+        fprintf(fp, "Greetings from child: %d\n", (int)getpid());
+    }
+    else
+    {
+        // we are in the parent branch
+        fprintf(fp, "Greetings from parent: %d\n", (int)getpid());
+    }
+    fclose(fp);
+
     return 0;
 }
+
+// Answer yes they were both able to write
+// The parent wrote first the the child

ex2/text.txt

@@ -0,0 +1,2 @@
+Greetings from parent: 10998
+Greetings from child: 10999

ex3/ex3.c

@@ -9,7 +9,23 @@
 
 int main(void)
 {
-    // Your code here
+    int f = fork();
+    if (f < 0)
+    {
+        printf("%s\n", "Fork faliled");
+        exit(1);
+    }
+    else if (f == 0)
+    {
+        // we are in the child branch
+        printf("%s\n", "hello");
+    }
+    else
+    {
+        // we are in the parent branch
+        wait(NULL);
+        printf("%s\n", "goodbye");
+    }
 
     return 0;
 }

ex4/ex4.c

@@ -1,6 +1,6 @@
 // Write a program that calls `fork()` and then calls some form of `exec()`
-// to run the program `/bin/ls`. Try a few variants of `exec()`, such as 
-// `execl()`, `execle()`, `execv()`, and others. Why do you think there 
+// to run the program `/bin/ls`. Try a few variants of `exec()`, such as
+// `execl()`, `execle()`, `execv()`, and others. Why do you think there
 // are so many variants of the same basic call?
 
 #include <stdio.h>
@@ -10,7 +10,25 @@
 
 int main(void)
 {
-    // Your code here    
+    int f = fork();
+    if (f < 0)
+    {
+        printf("%s\n", "Fork faliled");
+        exit(1);
+    }
+    else if (f == 0)
+    {
+        // we are in the child branch
+        char *args[] = {"ls", "-a", NULL};
+        // execvp(args[0], args);
+        execvp(args[0], args);
+    }
+    else
+    {
+        // we are in the parent branch
+        int wc = waitpid(f, NULL, 0);
+        printf("%s\n", "Child finished, exiting program");
+    }
 
     return 0;
 }

ex5/ex5.c

@@ -1,7 +1,7 @@
 // Write a program that forks a child and creates a shared pipe
-// between the parent and child processes. Have the child write 
-// the three messages to the parent and have the parent print out 
-// the messages. 
+// between the parent and child processes. Have the child write
+// the three messages to the parent and have the parent print out
+// the messages.
 
 #include <stdio.h>
 #include <unistd.h>
@@ -10,13 +10,46 @@
 
 #define MSGSIZE 16
 
-char* msg1 = "hello world #1";
-char* msg2 = "hello world #2";
-char* msg3 = "hello world #3";
+char *msg1 = "hello world #1";
+char *msg2 = "hello world #2";
+char *msg3 = "hello world #3";
 
 int main(void)
 {
     // Your code here
-
+    char inbuf[MSGSIZE];
+    int p[2];
+    if (pipe(p) < 0)
+    {
+        fprintf(stderr, "pipe failde\n");
+        exit(1);
+    }
+    int f = fork();
+    if (f < 0)
+    {
+        printf("%s\n", "Fork faliled");
+        exit(1);
+    }
+    else if (f == 0)
+    {
+        // we are in the child branch
+        close(p[0]); // close the read branch
+        write(p[1], msg1, MSGSIZE);
+        write(p[1], msg2, MSGSIZE);
+        write(p[1], msg3, MSGSIZE);
+        close(p[1]); // close the write branch
+    }
+    else
+    {
+        // we are in the parent branch
+        close(p[1]); // close the write branch
+        wait(NULL);
+        for (int i = 0; i < 3; i++)
+        {
+            read(p[0], inbuf, MSGSIZE);
+            printf("%s\n", inbuf);
+        }
+        close(p[0]); // close the read branch
+    }
     return 0;
 }

ex6/ex6.c

@@ -12,15 +12,27 @@ and `clock_gettime()` should work just fine.
 */
 
 #include <stdio.h>
-#include <unistd.h>
+#include <stdint.h>
+#include <stdlib.h>
 #include <time.h>
+#include <unistd.h>
 
 #define number_iter 1000000
 #define BILLION 1000000000L
 
+struct timespec start, end;
+
 int main()
 {
-    // Your code here
-
+    clock_gettime(CLOCK_MONOTONIC, &start);
+    for (int i = 0; i < number_iter; i++)
+    {
+        write(fileno(stdout), NULL, 0);
+    }
+    clock_gettime(CLOCK_MONOTONIC, &end);
+    double diff = BILLION * (end.tv_sec - start.tv_sec) + end.tv_nsec - start.tv_nsec;
+    double individual = diff / number_iter;
+    printf("Average time in nanoseconds: %lf\n", individual);
+
     return 0;
 }