Initial commit of libspinscale library

include/spinscale/qutexAcquisitionHistoryTracker.h

@@ -0,0 +1,164 @@
+#ifndef QUTEX_ACQUISITION_HISTORY_TRACKER_H
+#define QUTEX_ACQUISITION_HISTORY_TRACKER_H
+
+#include <unordered_map>
+#include <memory>
+#include <forward_list>
+#include <functional>
+#include "spinLock.h"
+
+
+namespace sscl {
+
+// Forward declarations
+class Qutex;
+class AsynchronousContinuationChainLink;
+class DependencyGraph;
+
+/**
+ * @brief QutexAcquisitionHistoryTracker - Tracks acquisition history for
+ *        gridlock detection
+ *
+ * This class maintains a central acquisition history to track all lockvokers
+ * suspected of being gridlocked. It stores information about what locks each
+ * timed-out lockvoker wants and what locks they hold in their continuation
+ * history.
+ */
+class QutexAcquisitionHistoryTracker
+{
+public:
+	/**
+	 * @brief Type definition for the acquisition history entry
+	 *
+	 * pair.first: The firstFailedQutex that this lockvoker WANTS but can't
+	 * acquire
+	 * pair.second: A unique_ptr to a list of all acquired Qutexes in this
+	 * lockvoker's continuation history
+	 */
+	typedef std::pair<
+		std::reference_wrapper<Qutex>,
+		std::unique_ptr<std::forward_list<std::reference_wrapper<Qutex>>>
+	> AcquisitionHistoryEntry;
+
+	/**
+	 * @brief Type definition for the acquisition history map
+	 *
+	 * Key: std::shared_ptr<AsynchronousContinuationChainLink>
+	 *		(the continuation that contains the timed-out lockvoker)
+	 * Value: AcquisitionHistoryEntry
+	 *		(its wanted lock (aka: firstFailedQutex/pair.first) + held locks)
+	 */
+	typedef std::unordered_map<
+		std::shared_ptr<AsynchronousContinuationChainLink>,
+		AcquisitionHistoryEntry
+	> AcquisitionHistoryMap;
+
+public:
+	static QutexAcquisitionHistoryTracker& getInstance()
+	{
+		static QutexAcquisitionHistoryTracker instance;
+		return instance;
+	}
+
+	/**
+	 * @brief Add a continuation to the acquisition history if it doesn't
+	 *	already exist
+	 * @param continuation Shared pointer to the
+	 *	AsynchronousContinuationChainLink
+	 * @param wantedLock The lock that this continuation wants but can't
+	 *	acquire
+	 * @param heldLocks Unique pointer to list of locks held in this
+	 *	continuation's history (will be moved)
+	 */
+	void addIfNotExists(
+		std::shared_ptr<AsynchronousContinuationChainLink> &continuation,
+		Qutex& wantedLock,
+		std::unique_ptr<std::forward_list<std::reference_wrapper<Qutex>>>
+			heldLocks
+		)
+	{
+		acquisitionHistoryLock.acquire();
+
+		auto it = acquisitionHistory.find(continuation);
+		// If a continuation already exists, don't add it again
+		if (it != acquisitionHistory.end())
+		{
+			acquisitionHistoryLock.release();
+			return;
+		}
+
+		acquisitionHistory.emplace(continuation, std::make_pair(
+			std::ref(wantedLock), std::move(heldLocks)));
+
+		acquisitionHistoryLock.release();
+	}
+
+	/**
+	 * @brief Remove a continuation from the acquisition history
+	 *
+	 * @param continuation Shared pointer to the
+	 *        AsynchronousContinuationChainLink to remove
+	 * @return true if the continuation was found and removed, false if not found
+	 */
+	bool remove(
+		std::shared_ptr<AsynchronousContinuationChainLink> &continuation
+		)
+	{
+		acquisitionHistoryLock.acquire();
+
+		auto it = acquisitionHistory.find(continuation);
+		if (it != acquisitionHistory.end())
+		{
+			acquisitionHistory.erase(it);
+
+			acquisitionHistoryLock.release();
+			return true;
+		}
+
+		acquisitionHistoryLock.release();
+		return false;
+	}
+
+	bool heuristicallyTraceContinuationHistoryForGridlockOn(
+		Qutex &firstFailedQutex,
+		std::shared_ptr<AsynchronousContinuationChainLink>&
+			currentContinuation);
+	bool completelyTraceContinuationHistoryForGridlockOn(
+		Qutex &firstFailedQutex);
+
+	/**
+	 * @brief Generates a dependency graph among known continuations, based on
+	 * the currently known acquisition history. There may well be a cyclical
+	 * dependency which hasn't been reported to the history tracker yet.
+	 * @param dontAcquireLock If true, skips acquiring the internal spinlock
+	 * (assumes caller already holds it)
+	 */
+	[[nodiscard]] std::unique_ptr<DependencyGraph> generateGraph(
+		bool dontAcquireLock = false);
+
+	// Disable copy constructor and assignment operator
+	QutexAcquisitionHistoryTracker(
+		const QutexAcquisitionHistoryTracker&) = delete;
+	QutexAcquisitionHistoryTracker& operator=(
+		const QutexAcquisitionHistoryTracker&) = delete;
+
+private:
+	QutexAcquisitionHistoryTracker() = default;
+	~QutexAcquisitionHistoryTracker() = default;
+
+private:
+	/**	EXPLANATION:
+	 * We use a SpinLock here instead of a Qutex because this acquisition
+	 * history tracker is invoked within the LockerAndInvoker.
+	 * Since LockerAndInvoker is too tightly coupled with Qutex workings, using
+	 * a Qutex here would create a circular dependency or deadlock situation.
+	 * Therefore, it's best to use a SpinLock on the history class to avoid
+	 * these coupling issues.
+	 */
+	SpinLock acquisitionHistoryLock;
+	AcquisitionHistoryMap acquisitionHistory;
+};
+
+} // namespace sscl
+
+#endif // QUTEX_ACQUISITION_HISTORY_TRACKER_H