Multithreaded C Program on the Raspberry PI

Currently, I am having a hard time to discover what the problem with my multithreading C program on the RPi is. I have written an application relying on two pthreads, one of them reading data from a gps device and writing it to a text file and the second one is doing exactly the same but with a temperature sensor. On my laptop (Intel® Core™ i3-380M, 2.53GHz) I am have the program nicely working and writing to my files up to the frequencies at which both of the devices send information (10 Hz and 500 Hz respectively).

The real problem emerges when I compile and execute my C program to run on the RPi; The performance of my program running on RPi considerably decreases, having my GPS log file written with a frequency of 3 Hz and the temperature log file at a frequency of 17 Hz (17 measurements written per second)..

I do not really know why I am getting those performance problems with my code running on the PI. Is it because of the RPi has only a 700 MHz ARM Processor and it can not process such a Multithreaded application? Or is it because my two threads routines are perturbing the nice work normally carried out by the PI? Thanks a lot in advance Guys….!!!

Here my code. I am posting just one thread function because I tested the performance with just one thread and it is still writing at a very low frequency (~4 Hz). At first, the main function:

int main(int argc, char *argv[]) {
    int s1_hand = 0;
    pthread_t routines[2];
    printf("Creating Thread -> Main Thread Busy!\n");

    s1_hand = pthread_create(&(routines[1]), NULL, thread_2, (void *)&(routines[1]));

    if (s1_hand != 0){
        printf("Not possible to create threads:[%s]\n", strerror(s1_hand));
        exit(EXIT_FAILURE);
    }
    pthread_join(routines[1], NULL);

    void* result;
    if ((pthread_join(routines[1], &result)) == -1) {
        perror("Cannot join thread 2");
        exit(EXIT_FAILURE);
    }
    pthread_exit(NULL);

    return 0;
}

Now, thread number 2 function:

void *thread_2(void *parameters) {
    printf("Thread 2 starting...\n");
    int fd, chars, parsing, c_1, parse, p_parse = 1;
    double array[3];
    fd =  open("dev/ttyUSB0", O_RDONLY | O_NOCTTY | O_SYNC);
    if (fd < 0){
        perror("Unable to open the fd!");
        exit (EXIT_FAILURE);
    }
    FILE *stream_a, *stream_b;
    stream_a = fdopen(fd, "r");
    stream_b = fopen (FILE_I, "w+");
    if (stream_a == NULL || stream_b == NULL){
        perror("IMPOSSIBLE TO CREATE STREAMS");
        exit(EXIT_FAILURE);
    }
    c_1 = fgetc(stream_a);
    parse = findit(p_parse, c_1, array);
    printf("First Parse Done -> (%i)\n", parse);
    while ((chars = fgetc(stream_a)) != EOF){
        parsing = findit(0, (uint8_t)chars, array);
        if (parsing == 1){
            printf("MESSAGE FOUND AND SAVED -> (%i)\n", parsing);
            fprintf(stream_b,"%.6f %.3f %.3f %.3f\n", time_stamp(), array[0], array[1], array[2]);
        }
    }
    fflush(stream_b);

    fclose(stream_b);
    fclose(stream_a);

    close(fd);

    pthread_exit(NULL);

    return 0;
} 

Note that on my thread 2 function I am using findit(), function which returns 0 or 1 in case of having found and parsed a message from the gps, writing the parsed info in my array (0 no found, 1 found and parsed). The function time_stamp() just call the clock_gettime(CLOCK_MONOTONIC, &time_stamp) function in order to have a time reference on each written event. Hope with this information you guys can help me. Thank you!