what is better pthread() or exec()?

I'm going to writing multi-thread/multi-process program. One thread read data from serial port. One thread, send this data to server. And main thread will initialize and monitor these two threads. But I consider to use pthread() or exec() to for my multi-thread/multi-process program. Can any one give me some comment? Should I use pthread() or exec()? What is advantage and disadvantage of pthread() and exec(). Thanks in advance.

URL: