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<title>Test/Framework/Runners/ThreadPool.hs</title>
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<pre><a name="line-1"></a><span class='hs-keyword'>module</span> <span class='hs-conid'>Test</span><span class='hs-varop'>.</span><span class='hs-conid'>Framework</span><span class='hs-varop'>.</span><span class='hs-conid'>Runners</span><span class='hs-varop'>.</span><span class='hs-conid'>ThreadPool</span> <span class='hs-layout'>(</span>
<a name="line-2"></a> <span class='hs-varid'>executeOnPool</span>
<a name="line-3"></a> <span class='hs-layout'>)</span> <span class='hs-keyword'>where</span>
<a name="line-4"></a>
<a name="line-5"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Concurrent</span>
<a name="line-6"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Control</span><span class='hs-varop'>.</span><span class='hs-conid'>Monad</span>
<a name="line-7"></a>
<a name="line-8"></a><span class='hs-keyword'>import</span> <span class='hs-keyword'>qualified</span> <span class='hs-conid'>Data</span><span class='hs-varop'>.</span><span class='hs-conid'>IntMap</span> <span class='hs-keyword'>as</span> <span class='hs-conid'>IM</span>
<a name="line-9"></a>
<a name="line-10"></a><span class='hs-keyword'>import</span> <span class='hs-conid'>Foreign</span><span class='hs-varop'>.</span><span class='hs-conid'>StablePtr</span>
<a name="line-11"></a>
<a name="line-12"></a>
<a name="line-13"></a><a name="WorkerEvent"></a><span class='hs-keyword'>data</span> <span class='hs-conid'>WorkerEvent</span> <span class='hs-varid'>token</span> <span class='hs-varid'>a</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>WorkerTermination</span>
<a name="line-14"></a> <span class='hs-keyglyph'>|</span> <span class='hs-conid'>WorkerItem</span> <span class='hs-varid'>token</span> <span class='hs-varid'>a</span>
<a name="line-15"></a>
<a name="line-16"></a><a name="executeOnPool"></a><span class='hs-comment'>-- | Execute IO actions on several threads and return their results in the original</span>
<a name="line-17"></a><span class='hs-comment'>-- order. It is guaranteed that no action from the input list is executed unless all</span>
<a name="line-18"></a><span class='hs-comment'>-- the items that precede it in the list have been executed or are executing at that</span>
<a name="line-19"></a><span class='hs-comment'>-- moment.</span>
<a name="line-20"></a><span class='hs-definition'>executeOnPool</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Int</span> <span class='hs-comment'>-- ^ Number of threads to use</span>
<a name="line-21"></a> <span class='hs-keyglyph'>-></span> <span class='hs-keyglyph'>[</span><span class='hs-conid'>IO</span> <span class='hs-varid'>a</span><span class='hs-keyglyph'>]</span> <span class='hs-comment'>-- ^ Actions to execute: these will be scheduled left to right</span>
<a name="line-22"></a> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-keyglyph'>[</span><span class='hs-varid'>a</span><span class='hs-keyglyph'>]</span> <span class='hs-comment'>-- ^ Ordered results of executing the given IO actions in parallel</span>
<a name="line-23"></a><span class='hs-definition'>executeOnPool</span> <span class='hs-varid'>n</span> <span class='hs-varid'>actions</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-24"></a> <span class='hs-comment'>-- Prepare the channels</span>
<a name="line-25"></a> <span class='hs-varid'>input_chan</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>newChan</span>
<a name="line-26"></a> <span class='hs-varid'>output_chan</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>newChan</span>
<a name="line-27"></a>
<a name="line-28"></a> <span class='hs-comment'>-- Write the actions as items to the channel followed by one termination per thread</span>
<a name="line-29"></a> <span class='hs-comment'>-- that indicates they should terminate. We do this on another thread for</span>
<a name="line-30"></a> <span class='hs-comment'>-- maximum laziness (in case one the actions we are going to run depend on the</span>
<a name="line-31"></a> <span class='hs-comment'>-- output from previous actions..)</span>
<a name="line-32"></a> <span class='hs-keyword'>_</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>forkIO</span> <span class='hs-varop'>$</span> <span class='hs-varid'>writeList2Chan</span> <span class='hs-varid'>input_chan</span> <span class='hs-layout'>(</span><span class='hs-varid'>zipWith</span> <span class='hs-conid'>WorkerItem</span> <span class='hs-keyglyph'>[</span><span class='hs-num'>0</span><span class='hs-keyglyph'>..</span><span class='hs-keyglyph'>]</span> <span class='hs-varid'>actions</span> <span class='hs-varop'>++</span> <span class='hs-varid'>replicate</span> <span class='hs-varid'>n</span> <span class='hs-conid'>WorkerTermination</span><span class='hs-layout'>)</span>
<a name="line-33"></a>
<a name="line-34"></a> <span class='hs-comment'>-- Spawn workers</span>
<a name="line-35"></a> <span class='hs-varid'>forM_</span> <span class='hs-keyglyph'>[</span><span class='hs-num'>1</span><span class='hs-keyglyph'>..</span><span class='hs-varid'>n</span><span class='hs-keyglyph'>]</span> <span class='hs-layout'>(</span><span class='hs-varid'>const</span> <span class='hs-varop'>$</span> <span class='hs-varid'>forkIO</span> <span class='hs-varop'>$</span> <span class='hs-varid'>poolWorker</span> <span class='hs-varid'>input_chan</span> <span class='hs-varid'>output_chan</span><span class='hs-layout'>)</span>
<a name="line-36"></a>
<a name="line-37"></a> <span class='hs-comment'>-- Short version: make sure we do the right thing if a test blocks on dead</span>
<a name="line-38"></a> <span class='hs-comment'>-- MVars or TVars.</span>
<a name="line-39"></a> <span class='hs-comment'>-- Long version: GHC is clever enough to throw an exception (BlockedOnDeadMVar</span>
<a name="line-40"></a> <span class='hs-comment'>-- or BlockedIndefinitely) when a thread is waiting for a MVar or TVar that can't</span>
<a name="line-41"></a> <span class='hs-comment'>-- be written to. However, it doesn't know anything about the handlers for those</span>
<a name="line-42"></a> <span class='hs-comment'>-- exceptions. Therefore, when a worker runs a test that causes this exception,</span>
<a name="line-43"></a> <span class='hs-comment'>-- since the main thread is blocking on the worker, the main thread gets the</span>
<a name="line-44"></a> <span class='hs-comment'>-- exception too despite the fact that the main thread will be runnable as soon</span>
<a name="line-45"></a> <span class='hs-comment'>-- as the worker catches its own exception. The below makes sure the main thread</span>
<a name="line-46"></a> <span class='hs-comment'>-- is always reachable by the GC, which is the mechanism for finding threads</span>
<a name="line-47"></a> <span class='hs-comment'>-- that are unrunnable.</span>
<a name="line-48"></a> <span class='hs-comment'>-- See also the ticket where SimonM (semi-cryptically) explains this:</span>
<a name="line-49"></a> <span class='hs-comment'>-- <a href="http://hackage.haskell.org/trac/ghc/ticket/3291">http://hackage.haskell.org/trac/ghc/ticket/3291</a></span>
<a name="line-50"></a> <span class='hs-comment'>--</span>
<a name="line-51"></a> <span class='hs-comment'>-- NB: this actually leaks stable pointers. We could prevent this by making</span>
<a name="line-52"></a> <span class='hs-comment'>-- takeWhileWorkersExist do |unsafePerformIO newStablePtr| when returning the</span>
<a name="line-53"></a> <span class='hs-comment'>-- lazily-demanded tail of the list, but its a bit of a pain. For now, just</span>
<a name="line-54"></a> <span class='hs-comment'>-- grit our teeth and accept the leak.</span>
<a name="line-55"></a> <span class='hs-sel'>_stablePtr</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>myThreadId</span> <span class='hs-varop'>>>=</span> <span class='hs-varid'>newStablePtr</span>
<a name="line-56"></a>
<a name="line-57"></a> <span class='hs-comment'>-- Return the results generated by the worker threads lazily and in</span>
<a name="line-58"></a> <span class='hs-comment'>-- the same order as we got the inputs</span>
<a name="line-59"></a> <span class='hs-varid'>fmap</span> <span class='hs-layout'>(</span><span class='hs-varid'>reorderFrom</span> <span class='hs-num'>0</span> <span class='hs-varop'>.</span> <span class='hs-varid'>takeWhileWorkersExist</span> <span class='hs-varid'>n</span><span class='hs-layout'>)</span> <span class='hs-varop'>$</span> <span class='hs-varid'>getChanContents</span> <span class='hs-varid'>output_chan</span>
<a name="line-60"></a>
<a name="line-61"></a><a name="poolWorker"></a><span class='hs-definition'>poolWorker</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Chan</span> <span class='hs-layout'>(</span><span class='hs-conid'>WorkerEvent</span> <span class='hs-varid'>token</span> <span class='hs-layout'>(</span><span class='hs-conid'>IO</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>Chan</span> <span class='hs-layout'>(</span><span class='hs-conid'>WorkerEvent</span> <span class='hs-varid'>token</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>IO</span> <span class='hs-conid'>()</span>
<a name="line-62"></a><span class='hs-definition'>poolWorker</span> <span class='hs-varid'>input_chan</span> <span class='hs-varid'>output_chan</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>do</span>
<a name="line-63"></a> <span class='hs-comment'>-- Read an action and work out whether we should continue or stop</span>
<a name="line-64"></a> <span class='hs-varid'>action_item</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>readChan</span> <span class='hs-varid'>input_chan</span>
<a name="line-65"></a> <span class='hs-keyword'>case</span> <span class='hs-varid'>action_item</span> <span class='hs-keyword'>of</span>
<a name="line-66"></a> <span class='hs-conid'>WorkerTermination</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>writeChan</span> <span class='hs-varid'>output_chan</span> <span class='hs-conid'>WorkerTermination</span> <span class='hs-comment'>-- Must have run out of real actions to execute</span>
<a name="line-67"></a> <span class='hs-conid'>WorkerItem</span> <span class='hs-varid'>token</span> <span class='hs-varid'>action</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyword'>do</span>
<a name="line-68"></a> <span class='hs-comment'>-- Do the action then loop</span>
<a name="line-69"></a> <span class='hs-varid'>result</span> <span class='hs-keyglyph'><-</span> <span class='hs-varid'>action</span>
<a name="line-70"></a> <span class='hs-varid'>writeChan</span> <span class='hs-varid'>output_chan</span> <span class='hs-layout'>(</span><span class='hs-conid'>WorkerItem</span> <span class='hs-varid'>token</span> <span class='hs-varid'>result</span><span class='hs-layout'>)</span>
<a name="line-71"></a> <span class='hs-varid'>poolWorker</span> <span class='hs-varid'>input_chan</span> <span class='hs-varid'>output_chan</span>
<a name="line-72"></a>
<a name="line-73"></a><a name="takeWhileWorkersExist"></a><span class='hs-comment'>-- | Keep grabbing items out of the infinite list of worker outputs until we have</span>
<a name="line-74"></a><span class='hs-comment'>-- recieved word that all of the workers have shut down. This lets us turn a possibly</span>
<a name="line-75"></a><span class='hs-comment'>-- infinite list of outputs into a certainly finite one suitable for use with reorderFrom.</span>
<a name="line-76"></a><span class='hs-definition'>takeWhileWorkersExist</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Int</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyglyph'>[</span><span class='hs-conid'>WorkerEvent</span> <span class='hs-varid'>token</span> <span class='hs-varid'>a</span><span class='hs-keyglyph'>]</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyglyph'>[</span><span class='hs-layout'>(</span><span class='hs-varid'>token</span><span class='hs-layout'>,</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span><span class='hs-keyglyph'>]</span>
<a name="line-77"></a><span class='hs-definition'>takeWhileWorkersExist</span> <span class='hs-varid'>worker_count</span> <span class='hs-varid'>events</span>
<a name="line-78"></a> <span class='hs-keyglyph'>|</span> <span class='hs-varid'>worker_count</span> <span class='hs-varop'><=</span> <span class='hs-num'>0</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>[]</span>
<a name="line-79"></a> <span class='hs-keyglyph'>|</span> <span class='hs-varid'>otherwise</span> <span class='hs-keyglyph'>=</span> <span class='hs-keyword'>case</span> <span class='hs-varid'>events</span> <span class='hs-keyword'>of</span>
<a name="line-80"></a> <span class='hs-layout'>(</span><span class='hs-conid'>WorkerTermination</span><span class='hs-conop'>:</span><span class='hs-varid'>events'</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-varid'>takeWhileWorkersExist</span> <span class='hs-layout'>(</span><span class='hs-varid'>worker_count</span> <span class='hs-comment'>-</span> <span class='hs-num'>1</span><span class='hs-layout'>)</span> <span class='hs-varid'>events'</span>
<a name="line-81"></a> <span class='hs-layout'>(</span><span class='hs-conid'>WorkerItem</span> <span class='hs-varid'>token</span> <span class='hs-varid'>x</span><span class='hs-conop'>:</span><span class='hs-varid'>events'</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'>-></span> <span class='hs-layout'>(</span><span class='hs-varid'>token</span><span class='hs-layout'>,</span> <span class='hs-varid'>x</span><span class='hs-layout'>)</span> <span class='hs-conop'>:</span> <span class='hs-varid'>takeWhileWorkersExist</span> <span class='hs-varid'>worker_count</span> <span class='hs-varid'>events'</span>
<a name="line-82"></a> <span class='hs-conid'>[]</span> <span class='hs-keyglyph'>-></span> <span class='hs-conid'>[]</span>
<a name="line-83"></a>
<a name="line-84"></a><a name="reorderFrom"></a><span class='hs-comment'>-- | This function carefully shuffles the input list so it in the total order</span>
<a name="line-85"></a><span class='hs-comment'>-- defined by the integers paired with the elements. If the list is @xs@ and</span>
<a name="line-86"></a><span class='hs-comment'>-- the supplied initial integer is @n@, it must be the case that:</span>
<a name="line-87"></a><span class='hs-comment'>--</span>
<a name="line-88"></a><span class='hs-comment'>-- > sort (map fst xs) == [n..n + (length xs - 1)]</span>
<a name="line-89"></a><span class='hs-comment'>--</span>
<a name="line-90"></a><span class='hs-comment'>-- This function returns items in the lazy result list as soon as it is sure</span>
<a name="line-91"></a><span class='hs-comment'>-- it has the right item for that position.</span>
<a name="line-92"></a><span class='hs-definition'>reorderFrom</span> <span class='hs-keyglyph'>::</span> <span class='hs-conid'>Int</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyglyph'>[</span><span class='hs-layout'>(</span><span class='hs-conid'>Int</span><span class='hs-layout'>,</span> <span class='hs-varid'>a</span><span class='hs-layout'>)</span><span class='hs-keyglyph'>]</span> <span class='hs-keyglyph'>-></span> <span class='hs-keyglyph'>[</span><span class='hs-varid'>a</span><span class='hs-keyglyph'>]</span>
<a name="line-93"></a><span class='hs-definition'>reorderFrom</span> <span class='hs-varid'>from</span> <span class='hs-varid'>initial_things</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>go</span> <span class='hs-varid'>from</span> <span class='hs-varid'>initial_things</span> <span class='hs-conid'>IM</span><span class='hs-varop'>.</span><span class='hs-varid'>empty</span> <span class='hs-conid'>False</span>
<a name="line-94"></a> <span class='hs-keyword'>where</span> <span class='hs-varid'>go</span> <span class='hs-varid'>next</span> <span class='hs-conid'>[]</span> <span class='hs-varid'>buf</span> <span class='hs-keyword'>_</span>
<a name="line-95"></a> <span class='hs-keyglyph'>|</span> <span class='hs-conid'>IM</span><span class='hs-varop'>.</span><span class='hs-varid'>null</span> <span class='hs-varid'>buf</span> <span class='hs-keyglyph'>=</span> <span class='hs-conid'>[]</span> <span class='hs-comment'>-- If the buffer and input list is empty, we're done</span>
<a name="line-96"></a> <span class='hs-keyglyph'>|</span> <span class='hs-varid'>otherwise</span> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>go</span> <span class='hs-varid'>next</span> <span class='hs-layout'>(</span><span class='hs-conid'>IM</span><span class='hs-varop'>.</span><span class='hs-varid'>toList</span> <span class='hs-varid'>buf</span><span class='hs-layout'>)</span> <span class='hs-conid'>IM</span><span class='hs-varop'>.</span><span class='hs-varid'>empty</span> <span class='hs-conid'>False</span> <span class='hs-comment'>-- Make sure we check the buffer even if the list is done</span>
<a name="line-97"></a> <span class='hs-varid'>go</span> <span class='hs-varid'>next</span> <span class='hs-varid'>all_things</span><span class='hs-keyglyph'>@</span><span class='hs-layout'>(</span><span class='hs-layout'>(</span><span class='hs-varid'>token</span><span class='hs-layout'>,</span> <span class='hs-varid'>x</span><span class='hs-layout'>)</span><span class='hs-conop'>:</span><span class='hs-varid'>things</span><span class='hs-layout'>)</span> <span class='hs-varid'>buf</span> <span class='hs-varid'>buf_useful</span>
<a name="line-98"></a> <span class='hs-keyglyph'>|</span> <span class='hs-varid'>token</span> <span class='hs-varop'>==</span> <span class='hs-varid'>next</span> <span class='hs-comment'>-- If the list token matches the one we were expecting we can just take the item</span>
<a name="line-99"></a> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>x</span> <span class='hs-conop'>:</span> <span class='hs-varid'>go</span> <span class='hs-layout'>(</span><span class='hs-varid'>next</span> <span class='hs-varop'>+</span> <span class='hs-num'>1</span><span class='hs-layout'>)</span> <span class='hs-varid'>things</span> <span class='hs-varid'>buf</span> <span class='hs-conid'>True</span> <span class='hs-comment'>-- Always worth checking the buffer now because the expected item has changed</span>
<a name="line-100"></a> <span class='hs-keyglyph'>|</span> <span class='hs-varid'>buf_useful</span> <span class='hs-comment'>-- If it's worth checking the buffer, it's possible the token we need is in it</span>
<a name="line-101"></a> <span class='hs-layout'>,</span> <span class='hs-layout'>(</span><span class='hs-conid'>Just</span> <span class='hs-varid'>x'</span><span class='hs-layout'>,</span> <span class='hs-varid'>buf'</span><span class='hs-layout'>)</span> <span class='hs-keyglyph'><-</span> <span class='hs-conid'>IM</span><span class='hs-varop'>.</span><span class='hs-varid'>updateLookupWithKey</span> <span class='hs-layout'>(</span><span class='hs-varid'>const</span> <span class='hs-varop'>$</span> <span class='hs-varid'>const</span> <span class='hs-conid'>Nothing</span><span class='hs-layout'>)</span> <span class='hs-varid'>next</span> <span class='hs-varid'>buf</span> <span class='hs-comment'>-- Delete the found item from the map (if we find it) to save space</span>
<a name="line-102"></a> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>x'</span> <span class='hs-conop'>:</span> <span class='hs-varid'>go</span> <span class='hs-layout'>(</span><span class='hs-varid'>next</span> <span class='hs-varop'>+</span> <span class='hs-num'>1</span><span class='hs-layout'>)</span> <span class='hs-varid'>all_things</span> <span class='hs-varid'>buf'</span> <span class='hs-conid'>True</span> <span class='hs-comment'>-- Always worth checking the buffer now because the expected item has changed</span>
<a name="line-103"></a> <span class='hs-keyglyph'>|</span> <span class='hs-varid'>otherwise</span> <span class='hs-comment'>-- Token didn't match, buffer unhelpful: it must be in the tail of the list</span>
<a name="line-104"></a> <span class='hs-keyglyph'>=</span> <span class='hs-varid'>go</span> <span class='hs-varid'>next</span> <span class='hs-varid'>things</span> <span class='hs-layout'>(</span><span class='hs-conid'>IM</span><span class='hs-varop'>.</span><span class='hs-varid'>insert</span> <span class='hs-varid'>token</span> <span class='hs-varid'>x</span> <span class='hs-varid'>buf</span><span class='hs-layout'>)</span> <span class='hs-conid'>False</span> <span class='hs-comment'>-- Since we've already checked the buffer, stop bothering to do so until something changes -}</span>
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