14. Advanced I/O
14.1. Introduction
This chapter covers numerous topics and functions that we lump under the term advanced I/O: nonblocking I/O, record locking, I/O multiplexing (the select and poll functions), asynchronous I/O, the readv and writev functions, and memory-mapped I/O (mmap). We need to cover these topics before describing interprocess communication in Chapter 15, Chapter 17, and many of the examples in later chapters.
14.2. Nonblocking I/O
In Section 10.5, we said that system calls are divided into two categories: the “slow” ones and all the others. The slow system calls are those that can block forever. They include
• Reads that can block the caller forever if data isn’t present with certain file types (pipes, terminal devices, ...
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