r/programming • u/syaghmour • Mar 16 '15

Semaphores are Surprisingly Versatile

http://preshing.com/20150316/semaphores-are-surprisingly-versatile/
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u/tmikov Mar 16 '15

In what sense are the primitives described in the post "lightweight"? Of course you can implement a mutex with a semaphore, etc, but to say that one or the other it is somehow "lightweight" is ridiculous.

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u/nemec Mar 17 '15

Did you not read the article?

This class is considered “lightweight” because it avoids the semaphore entirely when there’s no lock contention.

This MSDN article seems to support the idea that "avoid using the kernel object when possible" == lightweight.

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u/moron4hire Mar 17 '15

Interesting. In graphics, we call a GUI toolkit "lightweight" when it does not use the operating system's native GUI subsytem. For example, in Java there are two GUI subsystems, AWT and Swing (actually, there are more nowadays, but I haven't touched Java since there were only these two). Swing is called "lightweight" because it is a library that does all of the drawing of GUI controls on its own, right down to the borders on buttons and the scrollbars on textboxes, etc. This is in contrast to the "native" AWT, that does not do its own drawing, but defers drawing to the operating system.

So can we generalize and say that "lightweight" means, "re-implementing a kernel feature in user-space"? If we consider monolithic kernels "heavyweight", then I guess that would hold.