Andre Myrick - Processes & System Calls

ex1/ex1.c

@@ -2,13 +2,29 @@
 // (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?
 
+// In the program below, the parent process decrements and the child process increments. Because they are two separate processes running the 
+// code independently, x = 99 for the parent and x = 101 for the child.
+
 #include <stdio.h>
 #include <stdlib.h>
 #include <unistd.h>
 
 int main(void)
 {
-    // Your code here
+    int x = 100;
+    int pid = fork();
+    if (pid < 0) {
+        fprintf(stderr, "fork failed\n");
+        exit(1);
+    }
+
+    if (pid == 0) {
+        x++;
+    }
+    else {
+        x--;
+    }
+    printf("%d, %s, %d\n", pid, "hello", x);
 
     return 0;
 }

ex2/ex2.c

@@ -2,12 +2,31 @@
 // 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?
 
+// Both the child and the parent can access the file descriptor, if both processes attempt to write to the file then 
+// both attempts will be saved.
+
 #include <stdio.h>
 #include <unistd.h>
 #include <stdlib.h>
 
 int main(void)
 {
+    FILE *fp;
+
+    fp = fopen("text.txt", "r+");
+
+    int pid = fork();
+
+    if (pid == 0) {
+        fprintf(fp, "%s %s %s %s", "The", "child", "wrote", "this.");
+
+        fclose(fp);
+    }
+    else {
+        fprintf(fp, "%s %s %s %s", "The", "parent", "wrote", "this.");
+
+        fclose(fp);
+    }
     // Your code here 
 
     return 0;

ex2/text.txt

@@ -0,0 +1 @@
+The parent wrote this.The child wrote this.

ex3/ex3.c

@@ -9,7 +9,14 @@
 
 int main(void)
 {
-    // Your code here
+    int pid = fork();
+    waitpid(pid, NULL, 0); 
+    if (pid == 0) {
+        printf("%s\n", "hello");
+    }
+    else {
+        printf("%s\n", "goodbye");
+    }
 
     return 0;
 }

ex4/ex4.c

@@ -10,7 +10,9 @@
 
 int main(void)
 {
-    // Your code here    
+    char *args[]={"/bin/ls", NULL}; 
+    fork();
+    execv(args[0], args);    
 
     return 0;
 }

ex5/ex5.c

@@ -16,7 +16,30 @@ char* msg3 = "hello world #3";
 
 int main(void)
 {
-    // Your code here
-
+    char inbuf[MSGSIZE];
+    int p[2];               
+    if (pipe(p) < 0) {
+        fprintf(stderr, "pipe failed\n");
+        exit(1);
+    }
+    int pid = fork();
+
+    if (pid < 0) {
+        fprintf(stderr, "fork failed\n");
+        exit(1);
+    }
+
+    if (pid == 0) {
+        write(p[1], msg1, MSGSIZE);
+        write(p[1], msg2, MSGSIZE);
+        write(p[1], msg3, MSGSIZE);
+    }
+    else {
+        for (int i = 0; i < 3; i++) {
+        // read 16 bytes of data from the read file descriptor 
+            read(p[0], inbuf, MSGSIZE);
+            printf("%s\n", inbuf);
+        }
+    }
     return 0;
 }

ex6/ex6.c

@@ -12,6 +12,7 @@ and `clock_gettime()` should work just fine.
 */
 
 #include <stdio.h>
+#include <stdint.h>
 #include <unistd.h>
 #include <time.h>
 
@@ -20,7 +21,19 @@ and `clock_gettime()` should work just fine.
 
 int main()
 {
-    // Your code here
+    uint64_t diff;
+	struct timespec start, end;
+	int i;
+
+	clock_gettime(CLOCK_MONOTONIC, &start);
+	for (int i = 0; i < number_iter; i++)
+    {
+        write(fileno(stdout), NULL, 0);
+    }
+	clock_gettime(CLOCK_MONOTONIC, &end);
+
+	diff = BILLION * (end.tv_sec - start.tv_sec) + end.tv_nsec - start.tv_nsec;
+	printf("elapsed time = %llu nanoseconds\n", (long long unsigned int) diff);
 
     return 0;
 }

stretch/src/balance.txt

@@ -0,0 +1 @@
+8

stretch/src/bankers.c

@@ -86,12 +86,7 @@ void read_balance(int fd, int *balance)
  */
 int get_random_amount(void)
 {
-	// vvvvvvvvvvvvvvvvvv
-	// !!!! IMPLEMENT ME:
-
-	// Return a random number between 0 and 999 inclusive using rand()
-
-	// ^^^^^^^^^^^^^^^^^^
+	return rand() % 1000;
 }
 
 /**
@@ -116,16 +111,27 @@ int main(int argc, char **argv)
 	// message to stderr, and exit with status 1:
 	//
 	// "usage: bankers numprocesses\n"
+	if (argc < 2)
+	{
+		fprintf(stderr, "usage: bankers numprocessess\n");
+		exit(1);
+	}
 
 	// Store the number of processes in this variable:
 	// How many processes to fork at once
-	int num_processes = IMPLEMENT ME
+	int num_processes = strtol(argv[1], NULL, 10);
 
 	// Make sure the number of processes the user specified is more than
 	// 0 and print an error to stderr if not, then exit with status 2:
 	//
 	// "bankers: num processes must be greater than 0\n"
 
+	if (num_processes < 1)
+	{
+		fprintf(stderr, "bankers: num processes must be greater than 0\n");
+		exit(2);
+	}
+
 	// ^^^^^^^^^^^^^^^^^^
 
 	// Start with $10K in the bank. Easy peasy.
@@ -145,15 +151,36 @@ int main(int argc, char **argv)
 			int amount = get_random_amount();
 
 			int balance;
-
 			// vvvvvvvvvvvvvvvvvvvvvvvvv
 			// !!!! IMPLEMENT ME
-
+			fd = open_balance_file(BALANCE_FILE);
+			int lock = flock(fd, LOCK_EX);
+			if (lock < 0) 
+			{
+        		fprintf(stderr, "lock failed\n");
+        		exit(1);
+    		}
 			// Open the balance file (feel free to call the helper
 			// functions, above).
-
+
+			read_balance(fd, &balance);
 			// Read the current balance
-
+			if (balance > amount)
+			{
+				int new_balance = balance - amount;
+				write_balance(fd, new_balance);
+				printf("Withdrew $%d, new balance $%d\n", amount, new_balance);
+			} 
+			else
+			{
+				printf("Only have $%d, can't withdraw $%d\n", balance, amount);
+			}
+			int unlock = flock(fd, LOCK_UN);
+			if (unlock < 0) {
+        		fprintf(stderr, "unlock failed\n");
+        		exit(1);
+    		}
+
 			// Try to withdraw money
 			//
 			// Sample messages to print:
@@ -163,7 +190,7 @@ int main(int argc, char **argv)
 
 			// Close the balance file
 			//^^^^^^^^^^^^^^^^^^^^^^^^^^
-
+			close_balance_file(fd);
 			// Child process exits
 			exit(0);
 		}