99 lines
2.7 KiB
C++
99 lines
2.7 KiB
C++
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#ifndef STAR_OBSERVER_STREAM_HPP
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#define STAR_OBSERVER_STREAM_HPP
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#include "StarList.hpp"
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namespace Star {
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// Holds a stream of values which separate observers can query and track
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// occurrences in the stream without pulling them from the stream. Each
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// addition to the stream is given an abstract step value, and queries to the
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// stream can reference a given step value in order to track events since the
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// last query.
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template <typename T>
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class ObserverStream {
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public:
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ObserverStream(uint64_t historyLimit = 0);
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// If a history limit is set, then any entries with step values older than
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// the given limit will be discarded automatically. A historyLimit of 0
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// means that no values will be forgotten. The step value increases by one
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// with each entry added, or can be increased artificially by a call to
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// tickStep.
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uint64_t historyLimit() const;
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void setHistoryLimit(uint64_t historyLimit = 0);
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// Add a value to the end of the stream and increment the step value by 1.
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void add(T value);
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// Artificially tick the step by the given delta, which can be used to clear
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// older values.
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void tick(uint64_t delta = 1);
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// Query values in the stream since the given step value. Will return the
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// values in the stream, and a new since value to pass to query on the next
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// call.
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pair<List<T>, uint64_t> query(uint64_t since = 0) const;
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// Resets the step value to 0 and clears all values.
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void reset();
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private:
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uint64_t m_historyLimit;
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uint64_t m_nextStep;
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Deque<pair<uint64_t, T>> m_values;
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};
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template <typename T>
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ObserverStream<T>::ObserverStream(uint64_t historyLimit)
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: m_historyLimit(historyLimit), m_nextStep(0) {}
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template <typename T>
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uint64_t ObserverStream<T>::historyLimit() const {
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return m_historyLimit;
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}
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template <typename T>
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void ObserverStream<T>::setHistoryLimit(uint64_t historyLimit) {
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m_historyLimit = historyLimit;
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tick(0);
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}
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template <typename T>
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void ObserverStream<T>::add(T value) {
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m_values.append({m_nextStep, move(value)});
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tick(1);
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}
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template <typename T>
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void ObserverStream<T>::tick(uint64_t delta) {
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m_nextStep += delta;
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uint64_t removeBefore = m_nextStep - min(m_nextStep, m_historyLimit);
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while (!m_values.empty() && m_values.first().first < removeBefore)
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m_values.removeFirst();
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}
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template <typename T>
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pair<List<T>, uint64_t> ObserverStream<T>::query(uint64_t since) const {
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List<T> res;
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auto i = std::lower_bound(m_values.begin(),
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m_values.end(),
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since,
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[](pair<uint64_t, T> const& p, uint64_t step) { return p.first < step; });
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while (i != m_values.end()) {
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res.append(i->second);
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++i;
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}
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return {res, m_nextStep};
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}
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template <typename T>
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void ObserverStream<T>::reset() {
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m_nextStep = 0;
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m_values.clear();
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}
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}
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#endif
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