(In practice the A/B variable is a single bit, called the `IO Done'īit in Unix kernels, where this has been a standard idea for 'B' -> 'A' ( Becky provides final status of said service ).'A' -> 'B' ( Alice has placed a service request in the bucket ).Relationship, two simple state transitions suffice: Which requires no special locking primitive.įor example when the object being locked is a request/response bucketĪnd the two processes (Alice and Becky) have a fixed server-client However, did not provide such a primitive.Ī simpler method is available in many cases With multiprocessor hardware, the code fragment does not sufficeĪnd a (reliable) `memory compare and swap' (or when the command software otherwise forces serialization)ĭisab_intupt() /* should be `oldm = setint(DISABLE) */Įnabl_intupt() /* should be `(void)setint(oldm) ' */ When the underlying processing is done by a uniprocessor If Alice and Becky both attempt to acquire the same lock 'B' -> 0 ( process Becky releases its exclusive lock ).0 -> 'B' ( process Becky acquires the exclusive lock ).'A' -> 0 ( process Alice releases its exclusive lock ).0 -> 'A' ( process Alice acquires the exclusive lock ).Example 3.1: Locking semaphoresĪ typical `exclusive access' method might comprise S i m p l i c i t y m e a n s r e j e c t i n g u n n e e d e d r e q u i r e m e n t s. Not always easy to create or even define. Exercise: Knights on a 5x5 boardĪs promised we've given more definitions of simplicity. Example: Bloom filter 3.5 Simplicity doesn't imply laziness. Example: Hash tables 3.4 Simplicity is the inner beauty of elegance. Example: ISO 7-layer network model 3.3 Simplicity is not a substitute for study.
KERBAL SPACE PROGRAM ONLINE MOD HOW TO
Example: Exclusionary semaphores without locking 3.2 Simplicity is how to cope with complexity. Allen Introduction to Expert Programming (in C)įor this lesson, we discuss five further modes of simplicity,ģ.1 Simplicity means rejecting unneeded requirements. Introduction to Expert Programming (in C) Lesson 3Ĭopyright © 2003 by James D.
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