Processes in C- Farhan

ex1/ex1.c

@@ -2,13 +2,28 @@
 // (e.g., x) and set its value to something (e.g., 100). What value is the variable in the child process?
 // What happens to the variable when both the child and parent change the value of x?
 
+// Answer: At the start the child process has the same value (100).
+// When changed the variable has two values one on the main thread and one on the forked thread.
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
 
 int main(void)
 {
-    // Your code here
+
+    int x = 100;
+
+    if (x == 100){
+        int new_process = fork();
+        if (new_process){
+            printf("CP has same value as MP: %d\n", x);
+            printf("Child process will now change the val: ");
+            x = 10;
+        }
+
+    }
+    printf("From main process the value is left the same: %d\n", x);
 
     return 0;
 }

ex2/ex2.c

@@ -2,13 +2,28 @@
 // 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?
 
+// Answer: Yes they can both access the file descriptor. The file is written to 3 times. 
+
 #include <stdio.h>
 #include <unistd.h>
 #include <stdlib.h>
 
 int main(void)
 {
-    // Your code here 
+    FILE *fp;
+
+    fp = fopen ("text.txt", "r+");
+
+    fprintf(fp, "%s  %d\n", "We are in", getpid());
+
+    int new_process = fork();
+
+    if (new_process)
+    {
+        fprintf(fp, "%s  %d\n", "We are in", getpid());
+    }
+
+    fclose(fp);
 
     return 0;
 }

ex2/text.txt

@@ -0,0 +1,3 @@
+We are in  43508
+We are in  43508
+We are in  43508

ex3/ex3.c

@@ -6,10 +6,20 @@
 #include <stdlib.h>
 #include <unistd.h>
 #include <sys/wait.h>
+#include <strings.h>
 
 int main(void)
 {
-    // Your code here
+    int new_process = fork();
 
+    // Return value of fork()
+    // On success, the PID of the child process is returned in the parent, and 0 is returned in the child. 
+
+    if (new_process){
+        printf("hello from child\n");
+    } else {
+        printf("goodbye from main\n");
+    }
+
     return 0;
 }

ex3/tempCodeRunnerFile.c

@@ -0,0 +1,5 @@
+
+    int new_process = fork();
+    if (new_process){
+        printf("%s from child\n", hello);
+    }

ex4/ex4.c

@@ -10,7 +10,17 @@
 
 int main(void)
 {
-    // Your code here    
+    int new_process = fork();
+
+    // Return value of fork()
+    // On success, the PID of the child process is returned in the parent, and 0 is returned in the child. 
+
+    if (new_process){
+        // printf("hello from child\n");
+        execl("/bin/ls", "ls", NULL);
+    } else {
+        // printf("goodbye from main\n");
+    }   
 
     return 0;
 }

ex5/ex5.c

@@ -16,7 +16,34 @@ char* msg3 = "hello world #3";
 
 int main(void)
 {
-    // Your code here
+    char buf[MSGSIZE];
+    int p[2];               // a two-element array to hold the read and write file descriptors that are used by the pipe   
+
+    // establish our pipe, passing it the p array so that it gets populated by the read and write file descriptors
+    if (pipe(p) < 0) {
+        fprintf(stderr, "pipe failed\n");
+        exit(1);
+    }else {
+        int new_process = fork();
 
+        if (new_process){
+            printf("hello from child\n");
+             write(p[1], msg1, MSGSIZE);
+             write(p[1], msg2, MSGSIZE);
+             write(p[1], msg3, MSGSIZE);
+            printf("goodbye from child\n");
+
+        } else {
+            printf("hello from parent\n");
+            for (int i = 0; i < 3; i++) 
+            {
+            // read 16 bytes of data from the read file descriptor 
+            read(p[0], buf, MSGSIZE);
+            printf("\t%s\n", buf);
+            }
+            printf("goodbye from parent\n");
+        }
+    }
+
     return 0;
 }

ex6/ex6.c

@@ -20,7 +20,15 @@ and `clock_gettime()` should work just fine.
 
 int main()
 {
-    // Your code here
-
+    struct timespec start, end;
+    /* now re-do this and measure CPU time */
+	/* the time spent sleeping will not count (but there is a bit of overhead */
+	clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &start);	/* mark start time */
+	printf( "" );	/* write to stdout */
+	clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &end);		/* mark the end time */
+
+    uint64_t diff = BILLION * (end.tv_sec - start.tv_sec) + end.tv_nsec - start.tv_nsec;
+	printf("elapsed process CPU time = %llu nanoseconds\n", (long long unsigned int) diff);
+
     return 0;
 }