Chapter 12 -- Fibers

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Chapter 12

Microsoft added fibers to Windows to make it easy to port existing UNIX server applications to Windows. UNIX server applications are single-threaded (by the Windows definition) but can serve multiple clients. In other words, the developers of UNIX applications have created their own threading architecture library, which they use to simulate pure threads. This threading package creates multiple stacks, saves certain CPU registers, and switches among them to service the client requests.

Obviously, to get the best performance, these UNIX applications must be redesigned; the simulated threading library should be replaced with the pure threads offered by Windows. However, this redesign can take several months or longer to complete, so companies are first porting their existing UNIX code to Windows so they can ship something to the Windows market.

Problems can arise when you port UNIX code to Windows. In particular, the way in which Windows manages a thread stack is much more complex than simply allocating memory. Windows stacks start out with relatively little physical storage and grow as necessary. This process is described in the section titled "A Thread'sStack" in Chapter 16. Porting is also complicated by the structured exception handling mechanism (described in Chapters 23, 24, and 25).

To help companies port their code more quickly and correctly to Windows, Microsoft added fibers to the operating system. In this chapter, we'll examine the concept of a fiber, the functions that manipulate fibers, and how to take advantage of fibers. Keep in mind, of course, that you should avoid fibers in favor of more properly designed applications that use Windows native threads.