Question

Define asynchronous I/O and state what issue it addresses.

On a threaded system the issue isn’t as important as in a single threaded program why?

Answer 1

1.

Asynchronous I/O, or non-blocking I/O, is a form of input/output processing that permits other processing to continue before the transmission has finished.

What this means is, if a process wants to do a read() or write(), in a synchronous call, the process would have to wait until the hardware finishes the physical I/O so that it can be informed of the success/failure of the I/O operation.

On asynchronous mode, once the process issues a read/write I/O asynchronously, the system calls is returned immediately once the I/O has been passed down to the hardware or queued in the OS/VM. Thus the execution of the process isn't blocked (hence why it's called non-blocking I/O) since it doesn't need to wait for the result from the system call, it will receive the result later.

• Asynchronous I/O uses system resources more efficiently. Data copies from and to user buffers are asynchronous to the application that initiates the request. This overlapped processing makes efficient use of multiple processors and in many cases improves paging rates because system buffers are freed for reuse when data arrives.
• Asynchronous I/O minimizes process/thread wait time.
• Asynchronous I/O provides immediate service to client requests.
• Asynchronous I/O decreases the sleep and wake-up cost on average.
• Asynchronous I/O handles bursty application efficiently.
• Asynchronous I/O provides better scalability.
• Asynchronous I/O provides the most efficient method of handling large data transfers. The fillBuffer flag on the QsoStartRecv() API informs the operating system to acquire a large amount of data before completing the Asynchronous I/O. Large amounts of data can also be sent with one asynchronous operation.
• Asynchronous I/O minimizes the number of threads that are needed.
• Asynchronous I/O optionally can use timers to specify the maximum time allowed for this operation to complete asynchronously. Servers close a client connection if it has been idle for a set amount of time. The asynchronous timers allow the server to enforce this time limit.

NOTE: As per Chegg policy, I am allowed to answer only 1 long question (including sub-parts) on a single post. Kindly post the remaining questions separately and I will try to answer them. Sorry for the inconvenience caused.