Add ConsumableQueue helper container.
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source/eventcore/internal/consumablequeue.d
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169
source/eventcore/internal/consumablequeue.d
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module eventcore.internal.consumablequeue;
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/** FIFO queue with support for chunk-wise consumption.
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*/
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class ConsumableQueue(T)
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{
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nothrow:
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private {
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struct Slot {
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T value;
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uint rc;
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}
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Slot[] m_storage;
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size_t m_capacityMask;
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size_t m_first;
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size_t m_consumedCount;
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size_t m_pendingCount;
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}
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@property size_t length() const { return m_pendingCount; }
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/** Inserts a single element into the queue.
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*/
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@safe void put(T element)
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{
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reserve(1);
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auto idx = (m_first + m_consumedCount + m_pendingCount++) & m_capacityMask;
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m_storage[idx] = Slot(element, 0);
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}
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/** Reserves space for inserting at least `count` elements.
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*/
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void reserve(size_t count)
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@safe {
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auto min_capacity = m_consumedCount + m_pendingCount + count;
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if (min_capacity <= m_storage.length)
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return;
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auto new_capacity = m_storage.length ? m_storage.length : 16;
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while (new_capacity < min_capacity) new_capacity *= 2;
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auto new_capacity_mask = new_capacity - 1;
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auto new_storage = new Slot[new_capacity];
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foreach (i; 0 .. m_consumedCount + m_pendingCount)
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new_storage[(m_first + i) & new_capacity_mask] = m_storage[(m_first + i) & m_capacityMask];
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m_storage = new_storage;
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m_capacityMask = new_capacity_mask;
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}
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/** Consumes all elements of the queue and returns a range containing the
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consumed elements.
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Any elements added after the call to `consume` will not show up in the
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returned range.
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*/
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ConsumedRange consume()
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@safe {
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auto first = m_first;
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auto count = m_pendingCount;
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m_first += count;
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m_pendingCount = 0;
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return ConsumedRange(this, first, count);
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}
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static struct ConsumedRange {
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nothrow:
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private {
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ConsumableQueue m_queue;
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size_t m_first;
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size_t m_count;
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}
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this(ConsumableQueue queue, size_t first, size_t count)
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{
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m_queue = queue;
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m_queue.m_storage[first].rc++;
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m_first = first;
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m_count = count;
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}
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this(this)
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{
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m_queue.m_storage[m_first].rc++;
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}
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~this()
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{
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m_queue.consumed(m_first, false);
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}
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@property ConsumedRange save() { return this; }
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@property bool empty() const { return m_count == 0; }
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@property size_t length() const { return m_count; }
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@property ref inout(T) front() inout { return m_queue.m_storage[m_first].value; }
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void popFront()
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{
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m_queue.consumed(m_first, m_count > 1);
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m_first++;
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m_count--;
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}
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ref inout(T) opIndex(size_t idx) inout { return m_queue.m_storage[(m_first + idx) & m_queue.m_capacityMask].value; }
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int opApply(scope int delegate(ref T) @safe nothrow del)
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{
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foreach (i; 0 .. m_count)
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if (auto ret = del(m_queue.m_storage[(m_first + i) & m_queue.m_capacityMask].value))
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return ret;
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return 0;
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}
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}
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private void consumed(size_t first, bool shift_up)
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{
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if (shift_up) {
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if (!--m_storage[first].rc && first == m_first) {
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m_first++;
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m_consumedCount--;
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}
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m_storage[(first+1) & m_capacityMask].rc++;
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} else {
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m_storage[first].rc--;
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if (first == m_first)
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while (!m_storage[m_first].rc) {
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m_first++;
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m_consumedCount--;
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}
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}
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}
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}
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///
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unittest {
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import std.algorithm.comparison : equal;
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auto q = new ConsumableQueue!int;
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q.put(1);
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q.put(2);
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q.put(3);
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auto r1 = q.consume;
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assert(r1.length == 3);
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q.put(4);
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q.put(5);
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auto r2 = q.consume;
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assert(r2.length == 2);
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q.put(6);
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auto r3 = r1.save;
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assert(r3.length == 3);
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assert(r2.equal([4, 5]));
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assert(r1.equal([1, 2, 3]));
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assert(r3.equal([1, 2, 3]));
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assert(q.m_consumedCount == 0);
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assert(q.length == 1);
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assert(q.consume.equal([6]));
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assert(q.length == 0);
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}
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