| 1 | \chapter{\uC} \label{uC}
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| 2 |
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| 3 | \section{Introduction}
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| 4 | \uC \cite{Reference10} extends the \CC programming language with new
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| 5 | mechanisms to
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| 6 | facilitate control flow, and adds new objects to enable lightweight concurrency
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| 7 | on uniprocessor and parallel execution on multiprocessor computers. Concurrency has tasks
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| 8 | that can context switch, which is a control transfer from one execution state to
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| 9 | another that is different from a function call. Tasks are selected to run on a
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| 10 | processor from a ready queue of available tasks, and tasks may need to wait for an occurrence of an event.
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| 11 |
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| 12 | \section{Tasks}
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| 13 | A \textcolor{ForestGreen}{task} behaves like a class object, but it maintains its own
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| 14 | thread and execution state, which is the state information required to allow
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| 15 | independent execution. A task provides mutual exclusion by default for calls to its
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| 16 | public members. Public members allow communication among tasks.
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| 17 |
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| 18 | \section{\uC Runtime Structure}
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| 19 | \uC introduces two new runtime entities for controlling concurrent execution:
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| 20 | \begin{itemize}
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| 21 | \item Cluster
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| 22 | \item Virtual processor
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| 23 | \end{itemize}
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| 24 |
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| 25 | \subsection{Cluster}
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| 26 | A cluster is a group of tasks and virtual processors (discussed next) that
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| 27 | execute tasks. The objective of a cluster is to control the amount of possible
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| 28 | parallelism among tasks, which is only feasible if there are multiple
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| 29 | hardware processors (cores).
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| 30 |
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| 31 | At the start of a \uC program, two clusters are created. One is the system
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| 32 | cluster and the other is the user cluster. The system cluster has a processor
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| 33 | that only performs management work such as error detection and correction from
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| 34 | user clusters, if an execution in a user cluster results in errors, and cleans
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| 35 | up at shutdown. The user cluster manages and executes user tasks on its
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| 36 | processors. The benefits of clusters are maximizing utilization of processors
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| 37 | and minimizing runtime through a scheduler that is appropriate for a particular
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| 38 | workload. Tasks and virtual processors may be migrated among clusters.
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| 39 |
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| 40 | \subsection{Virtual Processor}
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| 41 | A virtual processor is a software emulation of a processor that executes
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| 42 | threads. Kernel threads are used to implement a virtual processor, which are
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| 43 | scheduled for execution on a hardware processor by the underlying operating
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| 44 | system. The operating system distributes kernel threads across a number of
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| 45 | processors assuming that the program runs on a multiprocessor architecture. The
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| 46 | usage of kernel threads enables parallel execution in \uC.
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