USB to Serial: LoopBack Read-Write Programs

Question

I am using BAFO bf-810 USB to Serial adapter with pl2303 drivers on Mac OS X. I am a beginner in the field and so have got the high level APIs from here which is a cross-platform API.

I have two programs, one to write and one to read. This API does not have a inbuilt samples in the code. So I had to look at other's APIs to get a picture of what had to be done (like, comOpen, comWrite etc.). With the limited knowledge, I wrote the following little programs using the linked APIs.

sendSerial.c

#include <stdio.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include "rs232.h"

extern int errno;

int main(){
    comEnumerate();

    if(!comOpen(1, 9600)) printf("Cannot open the port\n");

    while (1){
        char data[1024] = "Hello World";
        int ret = comWrite(1, data, 512);
        printf("%d\n", ret);
        if(ret>0){
            printf("Bytes transferred!\n");
        } else{
            printf("%s\n", strerror(errno));
        }
        sleep(1);
    }

    return 0;
}

.

recSerial.c

#include <unistd.h>
#include <stdio.h>
#include <errno.h>
#include "rs232.h"

extern int errno;

int main(){
    comEnumerate();
    if(!comOpen(1, 9600)) printf("Cannot open the port\n");

    char read[1024] = "EMPTY";

    printf("\nNow reading data at %s...\n",comGetPortName(1));

    while (1){
        printf(".\n");
        if(comRead(1, read, 4)){
            printf("Data: %s\n**\n", read);
        }
        sleep(1);
    }


    return 0;
}

The source has a single C program and might help on what I might be missing.

Question

When sending data, the write returns the Resource temporarily unavailable error after the third iteration. Why is this happening consistently? When I restart the sender program when the receiver is running, the error starts off with the first iteration itself.

In any case, I am not able to read any data on the read side of the program. I understand that the RS232 is an async protocol, but I've read somewhere that the system has a buffer of around 4 Mb before the data gets overwritten. So the second question is, do I have to manually handle the clock synchronisation?

P.S.: For the loopback test, I have connected, Send-Recieve, RTS-CTS and DTR-DSR on the DB9 connector.