Day One

ex1/ex1.c

@@ -9,6 +9,25 @@
 int main(void)
 {
     // Your code here
+    int x = 100;
+    int child = fork();
+    if (child < 0)
+    {
+      fprintf(stderr, "Nope fork failed.\n");
+      exit(1);
+    }
+    else if (child == 0)
+    {
+      printf("child start: %i \n", x);
+      x = 50;
+      printf("child end: %i \n", x);
+    }
+    else
+    {
+      printf("parent start: %i \n", x);
+      x = 60;
+      printf("parent end: %i \n", x);
+    }
 
     return 0;
 }

ex2/ex2.c

@@ -1,14 +1,42 @@
-// 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>
 #include <unistd.h>
 #include <stdlib.h>
+#include <string.h>
 
 int main(void)
 {
-    // Your code here 
-
+    // Your code here
+    FILE *txt = fopen("./text.txt", "w");
+    int child = fork();
+
+     if (child < 0)
+     {
+       fprintf(stderr, "Nope. fork failed");
+       exit(1);
+     }
+     else if (child == 0)
+     {
+       char *str1 = "The truth is out there\n";
+       fwrite(str1, sizeof(char), strlen(str1), txt);
+       // txt = fopen("text.txt", "a");
+       // fprintf(txt, "The truth is out there\n" );
+       // fclose(txt);
+       printf("child\n");
+     }
+     else
+     {
+       // txt = fopen("text.txt", "a");
+       // fprintf(txt, "Shut up Mulder\n");
+       // fclose(txt);
+       char *str2 = "Shut up Mulder\n";
+       fwrite(str2, sizeof(char), strlen(str2), txt);
+       printf("parent\n");
+     }
+     fclose(txt);
+
     return 0;
 }

ex2/text.txt

@@ -0,0 +1,2 @@
+Shut up Mulder
+The truth is out there

ex3/ex3.c

@@ -10,6 +10,21 @@
 int main(void)
 {
     // Your code here
+    int child = fork();
+    if (child < 0)
+    {
+      printf("Nope. Fork failed\n");
+      exit(1);
+    }
+    else if (child == 0)
+    {
+      printf("Knock knock\n");
+    }
+    else
+    {
+      waitpid(child, NULL, 0);
+      printf(" Who's there?\n");
+    }
 
     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 +10,23 @@
 
 int main(void)
 {
-    // Your code here    
-
+    // Your code here
+    int rc = fork();
+    if (rc < 0)
+    {
+      printf("Nope. Fork failed\n");
+      exit(1);
+    }
+    else if (rc == 0)
+    {
+      printf("hey that worked! (pid: %d)\n", getpid());
+      int run_it = execl("/bin/ls", "ls", "-1", NULL);
+      printf("run_it %d \n", run_it);
+    }
+    else
+    {
+      waitpid(rc, NULL, 0);;
+      printf("parent\n");
+    }
     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>
@@ -17,6 +17,41 @@ char* msg3 = "hello world #3";
 int main(void)
 {
     // Your code here
-
+    char buf[MSGSIZE];
+    int p[2];
+    if (pipe(p) < 0)
+    {
+      fprintf(stderr, "Nope. Pipe failed\n");
+      exit(1);
+    }
+    int rc = fork();
+
+    if (rc < 0)
+    {
+      printf("Nope. Fork failed\n");
+      exit(2);
+    }
+    else if (rc == 0)
+    {
+      printf("child writing\n");
+
+      write(p[1], msg1, MSGSIZE);
+      write(p[1], msg2, MSGSIZE);
+      write(p[1], msg3, MSGSIZE);
+
+      printf("child done\n");
+    }
+    else
+    {
+      waitpid(rc, NULL, 0);;
+      close(p[1]);
+      printf("parent\n");
+
+      while (read(p[0], buf, MSGSIZE) > 0)
+      {
+        printf("%s\n", buf);
+      }
+      printf("parent done\n");
+    }
     return 0;
 }

ex6/ex6.c

@@ -1,14 +1,14 @@
 /*
 Write a program that will find the average time it takes for your computer
-to make a system call an empty write to stdout. Your program should use the 
-`clock_gettime` procedure to time how long a single system call takes. It'll 
-do this for one million iterations, and then find the average of all of those 
+to make a system call an empty write to stdout. Your program should use the
+`clock_gettime` procedure to time how long a single system call takes. It'll
+do this for one million iterations, and then find the average of all of those
 iterations in nanoseconds.
 For some helpful documentation and examples of using time-related system calls,
 visit this site: https://www.cs.rutgers.edu/~pxk/416/notes/c-tutorials/gettime.html
-While the linked site does say that `clock_gettime()` does not work on OSX, this 
-turns out to only be the case for OSX versions < 10.12. Anything later than that 
-and `clock_gettime()` should work just fine. 
+While the linked site does say that `clock_gettime()` does not work on OSX, this
+turns out to only be the case for OSX versions < 10.12. Anything later than that
+and `clock_gettime()` should work just fine.
 */
 
 #include <stdio.h>
@@ -21,6 +21,24 @@ and `clock_gettime()` should work just fine.
 int main()
 {
     // Your code here
-
+
+    long sum = 0;
+    long time;
+    double avg;
+    struct timespec start, end;
+
+    for (int i = 0; i < number_iter; i++)
+    {
+      clock_gettime(CLOCK_MONOTONIC, &start);
+      write(fileno(stdout), NULL, 0);
+      clock_gettime(CLOCK_MONOTONIC, &end);
+
+      time = BILLION * (end.tv_sec - start.tv_sec) + (end.tv_nsec - start.tv_nsec);
+      sum += time;
+    }
+
+    avg = sum / (float) number_iter;
+    printf("Average is %f ns \n", avg);
+
     return 0;
 }