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</script></head><body><div id="package-header"><ul class="links" id="page-menu"><li><a href="src/Control-Concurrent-SSem.html">Source</a></li><li><a href="index.html">Contents</a></li><li><a href="doc-index.html">Index</a></li></ul><p class="caption">SafeSemaphore-0.9.0: Much safer replacement for QSemN, QSem, and SampleVar</p></div><div id="content"><div id="module-header"><table class="info"><tr><th>Portability</th><td>non-portable (concurrency)</td></tr><tr><th>Stability</th><td>experimental</td></tr><tr><th>Maintainer</th><td>haskell@list.mightyreason.com</td></tr><tr><th>Safe Haskell</th><td>Safe-Infered</td></tr></table><p class="caption">Control.Concurrent.SSem</p></div><div id="description"><p class="caption">Description</p><div class="doc"><p>Very simple quantity semaphore.
</p></div></div><div id="synopsis"><p id="control.syn" class="caption expander" onclick="toggleSection('syn')">Synopsis</p><ul id="section.syn" class="hide" onclick="toggleSection('syn')"><li class="src short"><span class="keyword">data</span> <a href="#t:SSem">SSem</a> </li><li class="src short"><a href="#v:new">new</a> :: <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/Data-Int.html#t:Int">Int</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/System-IO.html#t:IO">IO</a> <a href="Control-Concurrent-SSem.html#t:SSem">SSem</a></li><li class="src short"><a href="#v:withSem">withSem</a> :: <a href="Control-Concurrent-SSem.html#t:SSem">SSem</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/System-IO.html#t:IO">IO</a> a -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/System-IO.html#t:IO">IO</a> a</li><li class="src short"><a href="#v:wait">wait</a> :: <a href="Control-Concurrent-SSem.html#t:SSem">SSem</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/System-IO.html#t:IO">IO</a> <a href="/usr/share/doc/ghc/html/libraries/ghc-prim-0.2.0.0/GHC-Tuple.html#t:-40--41-">()</a></li><li class="src short"><a href="#v:signal">signal</a> :: <a href="Control-Concurrent-SSem.html#t:SSem">SSem</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/System-IO.html#t:IO">IO</a> <a href="/usr/share/doc/ghc/html/libraries/ghc-prim-0.2.0.0/GHC-Tuple.html#t:-40--41-">()</a></li><li class="src short"><a href="#v:tryWait">tryWait</a> :: <a href="Control-Concurrent-SSem.html#t:SSem">SSem</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/System-IO.html#t:IO">IO</a> (<a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/Data-Maybe.html#t:Maybe">Maybe</a> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/Data-Int.html#t:Int">Int</a>)</li><li class="src short"><a href="#v:withSemN">withSemN</a> :: <a href="Control-Concurrent-SSem.html#t:SSem">SSem</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/Data-Int.html#t:Int">Int</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/System-IO.html#t:IO">IO</a> a -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/System-IO.html#t:IO">IO</a> a</li><li class="src short"><a href="#v:waitN">waitN</a> :: <a href="Control-Concurrent-SSem.html#t:SSem">SSem</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/Data-Int.html#t:Int">Int</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/System-IO.html#t:IO">IO</a> <a href="/usr/share/doc/ghc/html/libraries/ghc-prim-0.2.0.0/GHC-Tuple.html#t:-40--41-">()</a></li><li class="src short"><a href="#v:signalN">signalN</a> :: <a href="Control-Concurrent-SSem.html#t:SSem">SSem</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/Data-Int.html#t:Int">Int</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/System-IO.html#t:IO">IO</a> <a href="/usr/share/doc/ghc/html/libraries/ghc-prim-0.2.0.0/GHC-Tuple.html#t:-40--41-">()</a></li><li class="src short"><a href="#v:tryWaitN">tryWaitN</a> :: <a href="Control-Concurrent-SSem.html#t:SSem">SSem</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/Data-Int.html#t:Int">Int</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/System-IO.html#t:IO">IO</a> (<a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/Data-Maybe.html#t:Maybe">Maybe</a> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/Data-Int.html#t:Int">Int</a>)</li><li class="src short"><a href="#v:getValue">getValue</a> :: <a href="Control-Concurrent-SSem.html#t:SSem">SSem</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/System-IO.html#t:IO">IO</a> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/Data-Int.html#t:Int">Int</a></li></ul></div><div id="interface"><h1>Documentation</h1><div class="top"><p class="src"><span class="keyword">data</span> <a name="t:SSem" class="def">SSem</a> <a href="src/Control-Concurrent-STM-SSemInternals.html#SSem" class="link">Source</a></p><div class="subs instances"><p id="control.i:SSem" class="caption collapser" onclick="toggleSection('i:SSem')">Instances</p><div id="section.i:SSem" class="show"><table><tr><td class="src"><a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/Data-Eq.html#t:Eq">Eq</a> <a href="Control-Concurrent-SSem.html#t:SSem">SSem</a></td><td class="doc empty"> </td></tr><tr><td class="src"><a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/Data-Typeable-Internal.html#t:Typeable">Typeable</a> <a href="Control-Concurrent-SSem.html#t:SSem">SSem</a></td><td class="doc empty"> </td></tr></table></div></div></div><div class="top"><p class="src"><a name="v:new" class="def">new</a> :: <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/Data-Int.html#t:Int">Int</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/System-IO.html#t:IO">IO</a> <a href="Control-Concurrent-SSem.html#t:SSem">SSem</a><a href="src/Control-Concurrent-SSem.html#new" class="link">Source</a></p><div class="doc"><p>Create a new semaphore with the given argument as the initially available quantity. This
allows new semaphores to start with a negative, zero, or positive quantity.
</p></div></div><div class="top"><p class="src"><a name="v:withSem" class="def">withSem</a> :: <a href="Control-Concurrent-SSem.html#t:SSem">SSem</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/System-IO.html#t:IO">IO</a> a -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/System-IO.html#t:IO">IO</a> a<a href="src/Control-Concurrent-SSem.html#withSem" class="link">Source</a></p><div class="doc"><p>It is recommended that all paired uses of <code><a href="Control-Concurrent-SSem.html#v:wait">wait</a></code> and <code><a href="Control-Concurrent-SSem.html#v:signal">signal</a></code> use the <code>with</code> bracketed form
to ensure exceptions safety.
</p></div></div><div class="top"><p class="src"><a name="v:wait" class="def">wait</a> :: <a href="Control-Concurrent-SSem.html#t:SSem">SSem</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/System-IO.html#t:IO">IO</a> <a href="/usr/share/doc/ghc/html/libraries/ghc-prim-0.2.0.0/GHC-Tuple.html#t:-40--41-">()</a><a href="src/Control-Concurrent-SSem.html#wait" class="link">Source</a></p><div class="doc"><p>Try to take a unit of value from the semaphore. This succeeds when the current quantity is
positive, and then reduces the quantity by one. Otherwise this will block and <code>retry</code> until it
succeeds or is killed. This will never result in a negative quantity. If several threads are
retying then which one succeeds next is undefined -- an unlucky thread might starve.
</p></div></div><div class="top"><p class="src"><a name="v:signal" class="def">signal</a> :: <a href="Control-Concurrent-SSem.html#t:SSem">SSem</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/System-IO.html#t:IO">IO</a> <a href="/usr/share/doc/ghc/html/libraries/ghc-prim-0.2.0.0/GHC-Tuple.html#t:-40--41-">()</a><a href="src/Control-Concurrent-SSem.html#signal" class="link">Source</a></p><div class="doc"><p>Signal that single unit of the semaphore is available. This increases the available quantity
by one.
</p></div></div><div class="top"><p class="src"><a name="v:tryWait" class="def">tryWait</a> :: <a href="Control-Concurrent-SSem.html#t:SSem">SSem</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/System-IO.html#t:IO">IO</a> (<a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/Data-Maybe.html#t:Maybe">Maybe</a> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/Data-Int.html#t:Int">Int</a>)<a href="src/Control-Concurrent-SSem.html#tryWait" class="link">Source</a></p><div class="doc"><p>Non-waiting version of wait. `tryWait s` is defined as `tryWaitN s 1`
</p></div></div><div class="top"><p class="src"><a name="v:withSemN" class="def">withSemN</a> :: <a href="Control-Concurrent-SSem.html#t:SSem">SSem</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/Data-Int.html#t:Int">Int</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/System-IO.html#t:IO">IO</a> a -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/System-IO.html#t:IO">IO</a> a<a href="src/Control-Concurrent-SSem.html#withSemN" class="link">Source</a></p><div class="doc"><p>It is recommended that all paired uses of <code><a href="Control-Concurrent-SSem.html#v:waitN">waitN</a></code> and <code><a href="Control-Concurrent-SSem.html#v:signalN">signalN</a></code> use the <code>withN</code>
bracketed form to ensure exceptions safety.
</p></div></div><div class="top"><p class="src"><a name="v:waitN" class="def">waitN</a> :: <a href="Control-Concurrent-SSem.html#t:SSem">SSem</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/Data-Int.html#t:Int">Int</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/System-IO.html#t:IO">IO</a> <a href="/usr/share/doc/ghc/html/libraries/ghc-prim-0.2.0.0/GHC-Tuple.html#t:-40--41-">()</a><a href="src/Control-Concurrent-SSem.html#waitN" class="link">Source</a></p><div class="doc"><p>Try to take the given value from the semaphore. This succeeds when the quantity is greater or
equal to the given value, and then subtracts the given value from the quantity. Otherwise this
will block and <code>retry</code> until it succeeds or is killed. This will never result in a negative
quantity. If several threads are retrying then which one succeeds next is undefined -- an
unlucky thread might starve.
</p></div></div><div class="top"><p class="src"><a name="v:signalN" class="def">signalN</a> :: <a href="Control-Concurrent-SSem.html#t:SSem">SSem</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/Data-Int.html#t:Int">Int</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/System-IO.html#t:IO">IO</a> <a href="/usr/share/doc/ghc/html/libraries/ghc-prim-0.2.0.0/GHC-Tuple.html#t:-40--41-">()</a><a href="src/Control-Concurrent-SSem.html#signalN" class="link">Source</a></p><div class="doc"><p>Signal that many units of the semaphore are available. This changes the available quantity by
adding the passed size.
</p></div></div><div class="top"><p class="src"><a name="v:tryWaitN" class="def">tryWaitN</a> :: <a href="Control-Concurrent-SSem.html#t:SSem">SSem</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/Data-Int.html#t:Int">Int</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/System-IO.html#t:IO">IO</a> (<a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/Data-Maybe.html#t:Maybe">Maybe</a> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/Data-Int.html#t:Int">Int</a>)<a href="src/Control-Concurrent-SSem.html#tryWaitN" class="link">Source</a></p><div class="doc"><p>Non-waiting version of waitN. It either takes the quantity from the semaphore like
waitN and returns `Just value taken` or finds insufficient quantity to take and returns
Nothing
</p></div></div><div class="top"><p class="src"><a name="v:getValue" class="def">getValue</a> :: <a href="Control-Concurrent-SSem.html#t:SSem">SSem</a> -> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/System-IO.html#t:IO">IO</a> <a href="/usr/share/doc/ghc/html/libraries/base-4.5.0.0/Data-Int.html#t:Int">Int</a><a href="src/Control-Concurrent-SSem.html#getValue" class="link">Source</a></p><div class="doc"><p>This returns the current quantity in the semaphore. This is diffucult to use due to race conditions.
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