Initial Commit - Lesson 31 (Commit #1)

Plugins/GameLiftServerSDK/ThirdParty/concurrentqueue/tests/CDSChecker/README.txt

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+These tests require CDSChecker to be checked out into a subdirectory
+named 'model-checker'.
+
+CDSChecker can be obtained from: git://demsky.eecs.uci.edu/model-checker.git
+The version last used for testing was: da671f78d0aa057272bb82f580b36a188b6331bd

Plugins/GameLiftServerSDK/ThirdParty/concurrentqueue/tests/CDSChecker/corealgo.h

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+// ©2013 Cameron Desrochers
+
+// Provides the core enqueue/dequeue algorithm of moodycamel::ConcurrentQueue
+// for testing with CDSChecker (a C++11 memory model checking tool).
+// See http://demsky.eecs.uci.edu/c11modelchecker.html for more info.
+
+#pragma once
+
+#include "model-checker/include/atomic"
+#include "model-checker/include/librace.h"
+#include "model-checker/include/model-assert.h"
+
+#ifndef CHAR_BIT
+#define CHAR_BIT 8
+#endif
+
+typedef unsigned int index_t;
+static std::atomic<index_t> headIndex;
+static std::atomic<index_t> tailIndex;
+static std::atomic<index_t> dequeueOvercommit;
+static std::atomic<index_t> dequeueOptimisticCount;
+
+static const unsigned int BLOCK_SIZE = 256;
+static int block[BLOCK_SIZE];
+
+static void init()
+{
+	headIndex.store(0, std::memory_order_relaxed);
+	tailIndex.store(0, std::memory_order_relaxed);
+	dequeueOvercommit.store(0, std::memory_order_relaxed);
+	dequeueOptimisticCount.store(0, std::memory_order_relaxed);
+}
+
+template<typename T>
+static inline bool circular_less_than(T a, T b)
+{
+	return static_cast<T>(a - b) > static_cast<T>(static_cast<T>(1) << static_cast<T>(sizeof(T) * CHAR_BIT - 1));
+}
+
+static void enqueue(int element)
+{
+	index_t currentTailIndex = tailIndex.load(std::memory_order_relaxed);
+	index_t newTailIndex = 1 + currentTailIndex;
+	
+	store_32(&block[currentTailIndex & (BLOCK_SIZE - 1)], element);
+	
+	tailIndex.store(newTailIndex, std::memory_order_release);
+}
+
+static bool try_dequeue(int& element)
+{
+	auto tail = tailIndex.load(std::memory_order_relaxed);
+	auto overcommit = dequeueOvercommit.load(std::memory_order_relaxed);
+	if (circular_less_than<index_t>(dequeueOptimisticCount.load(std::memory_order_relaxed) - overcommit, tail)) {
+		// Might be something to dequeue, let's give it a try
+		
+		// Note that this if is purely for performance purposes in the common case when the queue is
+		// empty and the values are eventually consistent -- we may enter here spuriously.
+		
+		// Note that whatever the values of overcommit and tail are, they are not going to change (unless we
+		// change them) and must be the same value at this point (inside the if) as when the if condition was
+		// evaluated.
+
+		// We insert an acquire fence here to synchronize-with the release upon incrementing dequeueOvercommit below.
+		// This ensures that whatever the value we got loaded into overcommit, the load of dequeueOptisticCount in
+		// the fetch_add below will result in a value at least as recent as that (and therefore at least as large).
+		// Note that I believe a compiler (signal) fence here would be sufficient due to the nature of fetch_add (all
+		// read-modify-write operations are guaranteed to work on the latest value in the modification order), but
+		// unfortunately that can't be shown to be correct using only the C++11 standard.
+		// See http://stackoverflow.com/questions/18223161/what-are-the-c11-memory-ordering-guarantees-in-this-corner-case
+		std::atomic_thread_fence(std::memory_order_acquire);
+		
+		// Increment optimistic counter, then check if it went over the boundary
+		auto myDequeueCount = dequeueOptimisticCount.fetch_add(1, std::memory_order_relaxed);
+		
+		// Note that since dequeueOvercommit must be <= dequeueOptimisticCount (because dequeueOvercommit is only ever
+		// incremented after dequeueOptimisticCount -- this is enforced in the `else` block below), and since we now
+		// have a version of dequeueOptimisticCount that is at least as recent as overcommit (due to the release upon
+		// incrementing dequeueOvercommit and the acquire above that synchronizes with it), overcommit <= myDequeueCount.
+		MODEL_ASSERT(overcommit <= myDequeueCount);
+		
+		// Note that we reload tail here in case it changed; it will be the same value as before or greater, since
+		// this load is sequenced after (happens after) the earlier load above. This is supported by read-read
+		// coherance (as defined in the standard), explained here: http://en.cppreference.com/w/cpp/atomic/memory_order
+		auto newTail = tailIndex.load(std::memory_order_acquire);
+		MODEL_ASSERT(newTail >= tail);
+		tail = newTail;
+		if (circular_less_than<index_t>(myDequeueCount - overcommit, tail)) {
+			// Guaranteed to be at least one element to dequeue!
+			
+			// Get the index. Note that since there's guaranteed to be at least one element, this
+			// will never exceed the true value of tail (but may exceed the value we read above).
+			auto index = headIndex.fetch_add(1, std::memory_order_acq_rel);
+			
+			// Dequeue
+			element = load_32(&block[index & (BLOCK_SIZE - 1)]);
+			
+			return true;
+		}
+		else {
+			// Wasn't anything to dequeue after all; make the effective dequeue count eventually consistent
+			dequeueOvercommit.fetch_add(1, std::memory_order_release);		// Release so that the fetch_add on dequeueOptimisticCount is guaranteed to happen before this write
+		}
+	}
+
+	return false;
+}
+
+static int size_approx()
+{
+	auto tail = tailIndex.load(std::memory_order_relaxed);
+	auto head = headIndex.load(std::memory_order_relaxed);
+	return circular_less_than(head, tail) ? static_cast<int>(tail - head) : 0;
+}

Plugins/GameLiftServerSDK/ThirdParty/concurrentqueue/tests/CDSChecker/enqueue_dequeue_many.cpp

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+// ©2013 Cameron Desrochers.
+// Distributed under the simplified BSD license (see the LICENSE file that
+// should have come with this file).
+
+#include "model-checker/include/threads.h"
+#include "corealgo.h"
+
+void consumer(void* param)
+{
+	int id = *(int*)param;
+	int& dequeueCount = *(int*)param;
+	dequeueCount = 0;
+	
+	int last = 0;
+	
+	int element;
+	bool success = try_dequeue(element);
+	if (success) {
+		MODEL_ASSERT(element > last);
+		last = element;
+		++dequeueCount;
+	}
+	success = try_dequeue(element);
+	if (success) {
+		MODEL_ASSERT(element > last);
+		last = element;
+		++dequeueCount;
+	}
+}
+
+void producer(void* param)
+{
+	for (int i = 1; i <= 8; ++i)
+		enqueue(i);
+
+	consumer(param);
+}
+
+int user_main(int, char**)
+{
+	init();
+	
+	// Start out as thread IDs, but are re-used by the threads
+	// to indicate the number of elements each one dequeued
+	int w = 1, x = 2, y = 3, z = 4;
+	
+	thrd_t a, b, c, d;
+	
+	thrd_create(&a, &producer, &w);
+	thrd_create(&b, &consumer, &x);
+	thrd_create(&c, &consumer, &y);
+	thrd_create(&d, &consumer, &z);
+	
+	thrd_join(a);
+	thrd_join(b);
+	thrd_join(c);
+	thrd_join(d);
+	
+	MODEL_ASSERT(w + x + y + z + size_approx() == 8);
+	
+	return 0;
+}

Plugins/GameLiftServerSDK/ThirdParty/concurrentqueue/tests/CDSChecker/enqueue_dequeue_one.cpp

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+// ©2013 Cameron Desrochers.
+// Distributed under the simplified BSD license (see the LICENSE file that
+// should have come with this file).
+
+#include "model-checker/include/threads.h"
+#include "corealgo.h"
+
+void producer_thread(void*)
+{
+	enqueue(1234);
+}
+
+void consumer_thread(void*)
+{
+	int element;
+	bool result = try_dequeue(element);
+	MODEL_ASSERT(!result || element == 1234);
+	
+	if (result) {
+		MODEL_ASSERT(!try_dequeue(element));
+	}
+}
+
+int user_main(int, char**)
+{
+	init();
+	
+	thrd_t p, c;
+	
+	thrd_create(&p, &producer_thread, nullptr);
+	thrd_create(&c, &consumer_thread, nullptr);
+	
+	thrd_join(p);
+	thrd_join(c);
+	
+	return 0;
+}

Plugins/GameLiftServerSDK/ThirdParty/concurrentqueue/tests/CDSChecker/makefile

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+default: enqueue_dequeue_one.o enqueue_dequeue_many.o
+
+enqueue_dequeue_one.o: CDSChecker makefile enqueue_dequeue_many.cpp enqueue_dequeue_one.cpp corealgo.h
+	g++ -std=c++11 -DNDEBUG -O3 enqueue_dequeue_one.cpp -o enqueue_dequeue_one.o -Lmodel-checker -lmodel
+
+enqueue_dequeue_many.o: CDSChecker makefile enqueue_dequeue_many.cpp corealgo.h
+	g++ -std=c++11 -DNDEBUG -O3 enqueue_dequeue_many.cpp -o enqueue_dequeue_many.o -Lmodel-checker -lmodel
+
+CDSChecker:
+	$(MAKE) -C model-checker
+
+run: enqueue_dequeue_one.o enqueue_dequeue_many.o
+	cd model-checker && ./run.sh ../enqueue_dequeue_one.o > ../enqueue_dequeue_one.log
+	cd model-checker && ./run.sh ../enqueue_dequeue_many.o > ../enqueue_dequeue_many.log