My son does not allow me to read any NEW book or magazine and always becomes cranky till I stop reading and hand over that book to him.
Initially I thought it might be temporary thing but now, it has become a ritual.
How do I deal with it?
My immediate impression is that it's a power struggle. He wants your attention. He wants you to play with him. He sees your reading material as the thing that is keeping you from interacting with him.
Unless your new material is suitable for children (and you don't mind it being torn etc.) then don't give him your things. Instead, put them away and play with him.
I don't have much time for myself at home while the kids are awake either. I accept this as a phase in their lives - and in my life. Forget about computer time, books, magazines - until after bedtime. That's time for yourself.
Once he grows older, he will learn to respect your time needs too. But 4 is too early for that. Accept it.
I try to think of the challenging time until then as an investment... effort now pays off later. It's probably not wise to draw too strong parallels between children and investments (long-term break even?) but it helps to realize that small children grow up and I should enjoy their childhood as much as I can!
Between two and five or so, kids are really testing out their impact on the world around them. They still also need a lot of time with you. They spend a lot of time asserting their own opinions and desires over the people around them and test the limits of what they can effect. Without all the verbal skills you have, especially related to emotions, they often turn to other means to get what they want. This is all done at only a sub or semi concious level, it is not as though they are thinking, "how can I manipulate mom and dad this time?" but they are learning new skills related to cause and effect and what effect they can have and testing those skills. This manifests itself in different ways and generally by the time they are four or five things are calmer than at two and three, but your child is reaching new levels of sophistication in his/her exertion of control.
Additionally, kids often just want what you have because you have it (you are pretty cool after-all) so when you combine this fact, with the fact that they are testing how much influence they can have, you have kids that get "moody" until they get what they want. I have taught both preschool (two to four years old) and Middleschool (adolscent years) and always laughed when people asked how I could switch from one to the other so easily - its the same thing! Older kids just have a bigger vocabulary of "bad words" and "moody tactics" (well, and the ability to deceive).
I suggest a three-fold approach: