[update] change 'usleep()' to 'add Runloop Source '

[birdmichael]

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My issue:

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What I have done:

i think should use an prefer other techniques like RunLoop scheduling.

https://developer.apple.com/library/mac/#documentation/Cocoa/Reference/Foundation/Classes/nsrunloop_Class/Reference/Reference.html

using usleep() will arise a lot of problems related to multithreading
using usleep() is not a good alternative, because it may block the GUI

[ChenYilong]

Reference:

• opencv source code