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gen_server:reply/2
reply(Client, Reply) –> Result
Types:
Client - see below
Reply = term()
Result = term()
This function can be used by a gen_server to explicitly send a reply to a client that called call/2,3 or multi_call/2,3,4, when the reply cannot be defined in the return value of Module:handle_call/3.
Client must be the From argument provided to the callback function. Reply is an arbitrary term, which will be given back to the client as the return value of call/2,3 or multi_call/2,3,4.
The return value Result is not further defined, and should always be ignored. 
Result :
if exchange the timer:sleep(3000) and timer:sleep(1000) the Result will be "gen_server:reply"
so the from process only receive the fast reply ,but the gen_server will execute both!
Why?
gen_server:reply/2 design as :
