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Lecture8n - COT 4600 Operating Systems Spring 2011 Click to...

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Click to edit Master subtitle style 8/1/11 Lecture 8 COT 4600 Operating Systems Spring 2011 Dan C. Marinescu Office: HEC 304 Office hours: Tu-Th 5:00 – 6:00 PM
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Lecture 8 8/1/11 n Last time: ¨ Networking- the Internet ¨ Naming; n Use by: value/name n Today: n Binding and indirection n Generic naming model ¨ Name mapping algorithms ¨ Comparing names; name discovery n Practical design of naming scheme ¨ Contexts ¨ Name overloading n Next time ¨ UNIX File System Lecture 8 – Tuesday, February 8, 2011 22
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Lecture 8 8/1/11 Naming n The three abstractions manipulate objects identified by name. n How could object A access object B: ¨ Make a copy of object B and include it in A “ use by value n Safe ° there is a single copy of B n How to implement sharing of object B? ¨ Pass to A the means to access B using its name ° use by reference n Not inherently safe ° both A and C may attempt to modify B at the same time. Need some form of concurrency control. 33
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Lecture 8 8/1/11 Binding and indirection n Names allow the system designer to: 1. organize the modules of a system and to define communication patterns among them 2. defer for a later time n to create object B referred to by object A n select the specific object A wishes to use n Indirection “ decoupling objects from their physical realization through names. n Binding ± linking the object to names. Examples: ¨ ° A compiler constructs n a table of variables and their relative address in the data section of the memory map of the process n a list of unsatisfied external references ¨ ° A linker binds the external references to modules from libraries 44
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Lecture 8 8/1/11 Generic naming model n Naming scheme ° strategy for naming. Consists of: ¨ Name space - the set of acceptable names; the alphabet used to select the symbols from and the syntax rules. ¨ Universe of values ° set of objects/values to be named ¨ Name mapping algorithm T resolves the names, establishes a correspondence between a name and an object/value ¨ Context – the environment in which the model operates. n Example: searching for John Smith in the White Pages in Orlando (one context) or in Tampa (another context). n Sometimes there is only one context ° universal name space; e.g., the SSNs. n Default context 55
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Lecture 8 8/1/11 Figure 2.10 from the textbook 66
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Lecture 8 8/1/11 Operations on names in the abstract model n Simple models: value ° RESOLVE (name, context) ¨ The interpreter: n Determines the version of the RESOLVE (which naming scheme is used) n Identifies the context n Locates the object ¨ Example: the processor n Complex models support: ¨ creation of new bindings: status · BIND(name, value, context) ¨ deletion of old bindings: status ° UNBIND(name, value) ¨ enumeration of name space: list ° ENUMERATE(context) ¨ comparing names status: result ° COMPARE(name1,name2) 77
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Lecture 8 8/1/11 Name mapping n Name to value mapping ¨ One-to-One q the name identifies a single object ¨ Many-to-One “ multiple names identify one objects (aliasing) ¨ One-to-Many °
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