58 lines
1.9 KiB
TeX
58 lines
1.9 KiB
TeX
\section{\module{mutex} ---
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Mutual exclusion support}
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\declaremodule{standard}{mutex}
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\sectionauthor{Moshe Zadka}{moshez@zadka.site.co.il}
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\modulesynopsis{Lock and queue for mutual exclusion.}
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The \module{mutex} module defines a class that allows mutual-exclusion
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via acquiring and releasing locks. It does not require (or imply)
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threading or multi-tasking, though it could be useful for
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those purposes.
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The \module{mutex} module defines the following class:
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\begin{classdesc}{mutex}{}
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Create a new (unlocked) mutex.
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A mutex has two pieces of state --- a ``locked'' bit and a queue.
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When the mutex is not locked, the queue is empty.
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Otherwise, the queue contains zero or more
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\code{(\var{function}, \var{argument})} pairs
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representing functions (or methods) waiting to acquire the lock.
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When the mutex is unlocked while the queue is not empty,
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the first queue entry is removed and its
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\code{\var{function}(\var{argument})} pair called,
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implying it now has the lock.
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Of course, no multi-threading is implied -- hence the funny interface
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for \method{lock()}, where a function is called once the lock is
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acquired.
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\end{classdesc}
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\subsection{Mutex Objects \label{mutex-objects}}
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\class{mutex} objects have following methods:
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\begin{methoddesc}{test}{}
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Check whether the mutex is locked.
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\end{methoddesc}
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\begin{methoddesc}{testandset}{}
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``Atomic'' test-and-set, grab the lock if it is not set,
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and return \code{True}, otherwise, return \code{False}.
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\end{methoddesc}
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\begin{methoddesc}{lock}{function, argument}
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Execute \code{\var{function}(\var{argument})}, unless the mutex is locked.
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In the case it is locked, place the function and argument on the queue.
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See \method{unlock} for explanation of when
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\code{\var{function}(\var{argument})} is executed in that case.
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\end{methoddesc}
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\begin{methoddesc}{unlock}{}
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Unlock the mutex if queue is empty, otherwise execute the first element
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in the queue.
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\end{methoddesc}
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