WPILib Reorganization

This is a major restructuring of the WPILib repository to simply build
procedures and remove the remnants of Maven from everything except the
eclipse plugins. Gradle files have been largely simplified or rewritten,
taking advantage of splitting up parts of the build into separate build
files for ease of reading.

The eclipse plugins are now in a separate project, as is ntcore. All
dependencies are resolved via Maven dependencies, with the
Jenkins-maintained WPILib repo. Project structures have also been
simplified: we no longer have separate subprojects inside wpilibc and
wpilibj. Where possible, these changes hav been done with git renames,
to make sure we still have full history for all repositories. Other
unrelated subprojects have also been broken out: OutlineViewer is now a
separate project.

Change-Id: Ib4e2a6e1a2f66427a14f16612b0e0d69ed661878

wpilibc/simulation/src/Notifier.cpp

@@ -0,0 +1,263 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) FIRST 2008. All Rights Reserved.							  */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in $(WIND_BASE)/WPILib.  */
+/*----------------------------------------------------------------------------*/
+
+#include "Notifier.h"
+#include "Timer.h"
+#include "Utility.h"
+#include "WPIErrors.h"
+
+Notifier *Notifier::timerQueueHead = nullptr;
+priority_recursive_mutex Notifier::queueMutex;
+int Notifier::refcount = 0;
+std::thread Notifier::m_task;
+std::atomic<bool> Notifier::m_stopped(false);
+
+/**
+ * Create a Notifier for timer event notification.
+ * @param handler The handler is called at the notification time which is set
+ * using StartSingle or StartPeriodic.
+ */
+Notifier::Notifier(TimerEventHandler handler, void *param)
+{
+	if (handler == nullptr)
+		wpi_setWPIErrorWithContext(NullParameter, "handler must not be nullptr");
+	m_handler = handler;
+	m_param = param;
+	m_periodic = false;
+	m_expirationTime = 0;
+	m_period = 0;
+	m_nextEvent = nullptr;
+	m_queued = false;
+	{
+		std::lock_guard<priority_recursive_mutex> sync(queueMutex);
+		// do the first time intialization of static variables
+		if (refcount == 0)
+		{
+			m_task = std::thread(Run);
+		}
+		refcount++;
+	}
+}
+
+/**
+ * Free the resources for a timer event.
+ * All resources will be freed and the timer event will be removed from the
+ * queue if necessary.
+ */
+Notifier::~Notifier()
+{
+	{
+		std::lock_guard<priority_recursive_mutex> sync(queueMutex);
+		DeleteFromQueue();
+
+		// Delete the static variables when the last one is going away
+		if (!(--refcount))
+		{
+      m_stopped = true;
+			m_task.join();
+		}
+	}
+
+	// Acquire the semaphore; this makes certain that the handler is
+	// not being executed by the interrupt manager.
+	std::lock_guard<priority_mutex> lock(m_handlerMutex);
+}
+
+/**
+ * Update the alarm hardware to reflect the current first element in the queue.
+ * Compute the time the next alarm should occur based on the current time and the
+ * period for the first element in the timer queue.
+ * WARNING: this method does not do synchronization! It must be called from somewhere
+ * that is taking care of synchronizing access to the queue.
+ */
+void Notifier::UpdateAlarm()
+{
+}
+
+/**
+ * ProcessQueue is called whenever there is a timer interrupt.
+ * We need to wake up and process the current top item in the timer queue as long
+ * as its scheduled time is after the current time. Then the item is removed or
+ * rescheduled (repetitive events) in the queue.
+ */
+void Notifier::ProcessQueue(uint32_t mask, void *params)
+{
+	Notifier *current;
+	while (true)				// keep processing past events until no more
+	{
+		{
+			std::lock_guard<priority_recursive_mutex> sync(queueMutex);
+			double currentTime = GetClock();
+			current = timerQueueHead;
+			if (current == nullptr || current->m_expirationTime > currentTime)
+			{
+				break;		// no more timer events to process
+			}
+			// need to process this entry
+			timerQueueHead = current->m_nextEvent;
+			if (current->m_periodic)
+			{
+				// if periodic, requeue the event
+				// compute when to put into queue
+				current->InsertInQueue(true);
+			}
+			else
+			{
+				// not periodic; removed from queue
+				current->m_queued = false;
+			}
+			// Take handler mutex while holding queue semaphore to make sure
+			//  the handler will execute to completion in case we are being deleted.
+			current->m_handlerMutex.lock();
+		}
+
+		current->m_handler(current->m_param);	// call the event handler
+		current->m_handlerMutex.unlock();
+	}
+	// reschedule the first item in the queue
+	std::lock_guard<priority_recursive_mutex> sync(queueMutex);
+	UpdateAlarm();
+}
+
+/**
+ * Insert this Notifier into the timer queue in right place.
+ * WARNING: this method does not do synchronization! It must be called from somewhere
+ * that is taking care of synchronizing access to the queue.
+ * @param reschedule If false, the scheduled alarm is based on the curent time and UpdateAlarm
+ * method is called which will enable the alarm if necessary.
+ * If true, update the time by adding the period (no drift) when rescheduled periodic from ProcessQueue.
+ * This ensures that the public methods only update the queue after finishing inserting.
+ */
+void Notifier::InsertInQueue(bool reschedule)
+{
+	if (reschedule)
+	{
+		m_expirationTime += m_period;
+	}
+	else
+	{
+		m_expirationTime = GetClock() + m_period;
+	}
+	if (timerQueueHead == nullptr || timerQueueHead->m_expirationTime >= this->m_expirationTime)
+	{
+		// the queue is empty or greater than the new entry
+		// the new entry becomes the first element
+		this->m_nextEvent = timerQueueHead;
+		timerQueueHead = this;
+		if (!reschedule)
+		{
+			// since the first element changed, update alarm, unless we already plan to
+			UpdateAlarm();
+		}
+	}
+	else
+	{
+		for (Notifier **npp = &(timerQueueHead->m_nextEvent); ; npp = &(*npp)->m_nextEvent)
+		{
+			Notifier *n = *npp;
+			if (n == nullptr || n->m_expirationTime > this->m_expirationTime)
+			{
+				*npp = this;
+				this->m_nextEvent = n;
+				break;
+			}
+		}
+	}
+	m_queued = true;
+}
+
+/**
+ * Delete this Notifier from the timer queue.
+ * WARNING: this method does not do synchronization! It must be called from somewhere
+ * that is taking care of synchronizing access to the queue.
+ * Remove this Notifier from the timer queue and adjust the next interrupt time to reflect
+ * the current top of the queue.
+ */
+void Notifier::DeleteFromQueue()
+{
+	if (m_queued)
+	{
+		m_queued = false;
+		wpi_assert(timerQueueHead != nullptr);
+		if (timerQueueHead == this)
+		{
+			// remove the first item in the list - update the alarm
+			timerQueueHead = this->m_nextEvent;
+			UpdateAlarm();
+		}
+		else
+		{
+			for (Notifier *n = timerQueueHead; n != nullptr; n = n->m_nextEvent)
+			{
+				if (n->m_nextEvent == this)
+				{
+					// this element is the next element from *n from the queue
+					n->m_nextEvent = this->m_nextEvent;	// point around this one
+				}
+			}
+		}
+	}
+}
+
+/**
+ * Register for single event notification.
+ * A timer event is queued for a single event after the specified delay.
+ * @param delay Seconds to wait before the handler is called.
+ */
+void Notifier::StartSingle(double delay)
+{
+	std::lock_guard<priority_recursive_mutex> sync(queueMutex);
+	m_periodic = false;
+	m_period = delay;
+	DeleteFromQueue();
+	InsertInQueue(false);
+}
+
+/**
+ * Register for periodic event notification.
+ * A timer event is queued for periodic event notification. Each time the interrupt
+ * occurs, the event will be immediately requeued for the same time interval.
+ * @param period Period in seconds to call the handler starting one period after the call to this method.
+ */
+void Notifier::StartPeriodic(double period)
+{
+	std::lock_guard<priority_recursive_mutex> sync(queueMutex);
+	m_periodic = true;
+	m_period = period;
+	DeleteFromQueue();
+	InsertInQueue(false);
+}
+
+/**
+ * Stop timer events from occuring.
+ * Stop any repeating timer events from occuring. This will also remove any single
+ * notification events from the queue.
+ * If a timer-based call to the registered handler is in progress, this function will
+ * block until the handler call is complete.
+ */
+void Notifier::Stop()
+{
+	{
+		std::lock_guard<priority_recursive_mutex> sync(queueMutex);
+		DeleteFromQueue();
+	}
+	// Wait for a currently executing handler to complete before returning from Stop()
+	std::lock_guard<priority_mutex> sync(m_handlerMutex);
+}
+
+void Notifier::Run() {
+    while (!m_stopped) {
+        Notifier::ProcessQueue(0, nullptr);
+        if (timerQueueHead != nullptr)
+        {
+            Wait(timerQueueHead->m_expirationTime - GetClock());
+        }
+        else
+        {
+            Wait(0.05);
+        }
+    }
+}