Initial commit.

programming-assignment.c

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+#include <pthread.h>
+#include <stdio.h>
+#include <errno.h>
+#include <unistd.h>
+#include <stdlib.h>
+#include <string.h>
+#include <signal.h>
+
+/**************************************************************************
+ * Authors: Gary Fleming, Amber McCloughan
+ * Class: CIS452 - Operating Systems Concepts
+ * Professor: Dr. Greg Wolffe
+ * Date: 2/14/2019
+ * 
+ * Program that starts out with a dispatcher thread. This thread
+ * waits on user input. When it receives a filename string from 
+ * the user, it spawns a worker thread that goes out to 
+ * "retrieve" the filename from the "file server". On an exit,
+ * the program prints statistics about files serviced.
+ *
+ * To end the program, do a Ctrl + C.
+***************************************************************************/
+
+// Input limit.
+#define CHAR_LIMIT 1024
+
+// See function implementations for information.
+void *file_request(void *arg);
+void sigHandler(int);
+
+// File counter.
+int counter;
+
+// File access time counter.
+int timeCounter;
+
+// Mutex.
+pthread_mutex_t lock;
+
+// Input buffer.
+char *input;
+
+/**
+ * The main function for driving the program.
+ */
+int main()
+{
+    // Seeding randomness.
+    srand(time(NULL));
+
+    /*
+	 * Initializing the mutex.
+	 * I figured out how to do this using the following article:
+	 * https://www.geeksforgeeks.org/mutex-lock-for-linux-thread-synchronization/
+	 */
+    pthread_mutex_init(&lock, NULL);
+
+    // Thread ID holder.
+    pthread_t thread1;
+
+    // Status variable for checking if pthread_create failed.
+    int status;
+
+    // Initializing file counter.
+    counter = 0;
+
+    // Allocating memory for input buffer.
+    input = malloc(CHAR_LIMIT * sizeof(char));
+
+    // Binding signal handler for keyboard interrupt.
+    signal(SIGINT, sigHandler);
+
+    // The dispatching loop.
+    while (1)
+    {
+        // User input for filename.
+        fprintf(stderr, "Enter file name: ");
+        input = fgets(input, CHAR_LIMIT, stdin);
+
+        // Removing newline character from input.
+        strtok(input, "\n");
+
+        // Spawning a thread to deal with the "file" requested.
+        if ((status = pthread_create(&thread1, NULL, file_request, strdup(input))) != 0)
+        {
+            fprintf(stderr, "Thread creation error %d: %s.\n", status, strerror(status));
+            exit(1);
+        }
+    }
+
+    return 0;
+}
+
+/**
+ * Function executed by worked threads. Randomly decides
+ * whether the "file" can be accessed from the disk cache
+ * (80% chance) or if it has to be fetched from the hard 
+ * drive (20% chance). If the "file" is accessed from cache,
+ * the thread sleeps for a second. If the "file" is accessed
+ * from the hard drive, the thread sleeps for 7-10 seconds.
+ * A mutex is used to ensure mutual exclusion for writes.
+ *
+ * @param arg, the name of the "file" to be handled by the 
+ * worker thread.
+ */
+void *file_request(void *arg)
+{
+    // Probability roll for HDD or cache.
+    int val = (rand() % 5) + 1;
+
+    // Variable used for sleep time.
+    int val2;
+
+    // File accessed from disk.
+    if (val == 5)
+    {
+        // 7-10 seconds.
+        val2 = (rand() % 4) + 7;
+    }
+    // File accessed from cache.
+    else
+    {
+        // 1 second.
+        val2 = 1;
+    }
+
+    // Sleep for seconds decided on above.
+    sleep(val2);
+
+    // Serving the file.
+    fprintf(stderr, "\nServing file \"%s\" after %i seconds.\n", (char *)arg, val2);
+
+    // Writing to global variables. Mutex lock!
+    pthread_mutex_lock(&lock);
+    counter++;
+    timeCounter += val2;
+    pthread_mutex_unlock(&lock);
+
+    // Freeing allocated memory.
+    free(arg);
+
+    // Goodbye (no need to return anything).
+    return NULL;
+}
+
+/**
+ * Handler for signals. Bound for the one signal handled 
+ * in this application: SIGINT (program interrupt signal ^C). 
+ *
+ * @param sigNum, the identifying number of the signal
+ * 	sent and now being handled. According to the 
+ * 	man page for signal, SIGINT = 2.
+ */
+void sigHandler(int sigNum)
+{
+    if (sigNum == SIGINT)
+    {
+        // Exit message.
+        printf(" received. That's it, I'm shutting you down...\n");
+        printf("Files serviced: %i.\n", counter);
+        printf("Avg. file access time: %lf seconds.\n", (double)timeCounter / (double)counter);
+
+        // Destroying mutex.
+        pthread_mutex_destroy(&lock);
+
+        // Freeing user input pointer.
+        free(input);
+
+        // Exiting program.
+        exit(0);
+    }
+}