timeout in the first Marshal/Unmarshal when the struct is very deep

[liuq19]

A very deep and large struct is pretouched at first, then, it is marshaled or unmarshaled in TestTimeOutOp.
And all time is recorded.

command:

 go test -v  -count=4 -run TestTimeOutOp

output:

Pretouch time is: 2.023615109s
Pretouch done
=== RUN   TestTimeOutOp
==================
==================
The marshal and unmarshal time is: 3.511962887s
--- PASS: TestTimeOutOp (3.51s)
=== RUN   TestTimeOutOp
==================
==================
The marshal and unmarshal time is: 3.595865ms
--- PASS: TestTimeOutOp (0.00s)
=== RUN   TestTimeOutOp
==================
==================
The marshal and unmarshal time is: 4.327786ms
--- PASS: TestTimeOutOp (0.00s)
=== RUN   TestTimeOutOp
==================
==================
The marshal and unmarshal time is: 19.701935ms
--- PASS: TestTimeOutOp (0.02s)
PASS