Question

What is blocking in simple language in operating system?

Answer 1

n simple words blocking IO is something like "you waiting for your girl to join you on a date, you wait for her indefinitely", non-blocking IO is like "you have asked someone to join you on a date, but you are not sure if she turns up so early, so you decide to do other works pending, or sometimes you get bored and may try asking another girl for a date".

Above definition is just lame and actual meaning is as follows,

Blocking and Non-Blocking IO are two different possible ways of servicing any IO operation. It is easy to understand the concept if you try to understand it from literal meaning, let me break it down :

Blocking IO : From the name, we know that something is being blocked for IO operation. So, next we shall know what is being blocked, why is it getting blocked ?  

IO operation are completed at hardware at base level, blocking here means the normal operation of your system is set to wait state until your IO operation is completed. In other words you cannot do anything unless whatever operations requested are being serviced.

This is the technique used in all synchronous devices or real-time systems, in cases where you expect your IO to complete for further processing. This comes with disadvantage of over waiting for operations to complete and system getting stalled, but IO operations are guaranteed to be safe and data is not obsolete or data is consistent.

Non-blocking IO : Here the IO operations are performed independent of other system operations. Your system won’t let you to go into wait state, rather it can perform other operations which are independent of required IO.

Response from IO devices are furnished to the system once the operation completes, however system wouldn't stall in that time. Once you get the response, it can trigger some function to be completed. Any new requests sent to the same IO device will be queued and responses are also returned one after other. This is mostly achieved through parallel programming / creating multiple threads for each IO.