Comparative analysis of asynchronous I/O in multithreaded UNIX

I/O operations in UNIX are inherently synchronous. The need for asynchronous I/O comes first from multithreaded applications where thrads cannot block for I/O, and second from the fact that asynchronous I/O has much less overhead than synchronous I/O. There are two main approaches to accomplishing asynchronous I/O in UNIX. We compare the two approaches in design and implementation, and report the results of extensive experiments to measure the performance differences.