writeOutput.c

// take list message and write to screen

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <pthread.h>
#include <unistd.h>

#include "list.h"
#include "queueOperations.h"
#include "writeOutput.h"

// Max size of the message, using theoretical max length for a UDP packet of 65507 - 1 byte for null terminator
#define MAXBUFLEN 65506

static pthread_t writerThread;
static pthread_mutex_t writeAvailableCondMutex = PTHREAD_MUTEX_INITIALIZER;
static pthread_cond_t writeAvailableCond = PTHREAD_COND_INITIALIZER;
static List* list;
static char* message;

static void* writeLoop(void* useless){

    while(1)
    {
        // Waits the write funtion, will be signalled by receiveUDP
        pthread_mutex_lock(&writeAvailableCondMutex);
        {
            pthread_cond_wait(&writeAvailableCond, &writeAvailableCondMutex);
        }
        pthread_mutex_unlock(&writeAvailableCondMutex);
        
        int iteration = 0;

        do
        {
            iteration ++;

            // Taking message from list
            message = dequeueMessage(list);

            if(message==NULL)
            {
                fprintf(stderr, "writer: dequeue error, queue empty.\n");
                break;
            }

            int writeVar = write(1,message, strlen(message)); // will put the message from first list onto screen
            if(writeVar == -1){
                perror("Error in write() : Unable to write to screen");
                exit(-1);
            }

            // Checking for exit code
            if(!strcmp(message, "!\n") && iteration == 1)
            {
                free(message);
                message = NULL;
                return NULL;
            }

            // Freeing message (message is dynamically allocated from receiver)
            free(message);
            message = NULL;
        } while (countMessages(list)!=0);
    }
    return NULL;
    
}

void writerSignaller()
{
    //Signals the writer, will be called by receiveUDP
    pthread_mutex_lock(&writeAvailableCondMutex);
    {
        pthread_cond_signal(&writeAvailableCond);
    }
    pthread_mutex_unlock(&writeAvailableCondMutex);
}


void writerInit(List* l){

    list = l;

    int writingThread =  pthread_create(&writerThread, NULL, writeLoop, NULL);
    if(writingThread != 0){
        perror("write thread failed");
        exit(-1);
    }

}

void writerCancel()
{
    pthread_cancel(writerThread);
}

void writerShutdown()
{
    // De-allocating dynamically allocated message if shutdown is called while message is not yet freed
    // Note: if we HAVE already freed the pointer, then we've set the message pointer to NULL
    // and it is okay to free a NULL pointer (it does nothing)
    free(message);
    message = NULL;

    pthread_join(writerThread, NULL);
}