[WIP] Batch pushes and pops

README.md

@@ -166,9 +166,13 @@ push()                          pop()
 ### Queue API
 The queue class templates provide the following member functions:
 * `try_push` - Appends an element to the end of the queue. Returns `false` when the queue is full.
+* `try_push` (batch) - Appends an iterator range to the end of the queue. Returns the iterator one past the last element that got pushed, which could be different from the last iterator when the queue becomes full.
 * `try_pop` - Removes an element from the front of the queue. Returns `false` when the queue is empty.
+* `try_pop` (batch) - Removes elements from the front of the queue and places them into an iterator. Returns the number of elements popped, which may be different from the number of requested elements if the queue becomes empty.
 * `push` (optimist) - Appends an element to the end of the queue. Busy waits when the queue is full. Faster than `try_push` when the queue is not full. Optional FIFO producer queuing and total order.
+* `push` (optimist, batch) - Appends an iterator range to the end of the queue. Busy waits when the queue is full. Returns the iterator past the last pushed element. Faster than `try_push` when the queue is not full. Optional FIFO producer queuing and total order.
 * `pop` (optimist) - Removes an element from the front of the queue. Busy waits when the queue is empty. Faster than `try_pop` when the queue is not empty. Optional FIFO consumer queuing and total order.
+* `pop` (optimist, batch) - Removes elements from the front of the queue and places them into an iterator. Returns the iterator past the last popped element. Busy waits when the queue is empty. Faster than `try_pop` when the queue is not empty. Optional FIFO consumer queuing and total order.
 * `was_size` - Returns the number of unconsumed elements during the call. The state may have changed by the time the return value is examined.
 * `was_empty` - Returns `true` if the container was empty during the call. The state may have changed by the time the return value is examined.
 * `was_full` - Returns `true` if the container was full during the call. The state may have changed by the time the return value is examined.

include/atomic_queue/atomic_queue.h

@@ -10,6 +10,7 @@
 #include <cassert>
 #include <cstddef>
 #include <cstdint>
+#include <iterator>
 #include <memory>
 #include <utility>
 
@@ -389,6 +390,33 @@ class AtomicQueueCommon {
         return true;
     }
 
+    template<class InputIt>
+    ATOMIC_QUEUE_INLINE InputIt try_push(InputIt first, InputIt const last) noexcept {
+        int n = static_cast<int>(std::distance(first, last));
+        auto head = head_.load(X);
+        if(Derived::spsc_) {
+            int const slots = static_cast<int>(tail_.load(X) + downcast().size_ - head);
+            n = std::min(n, slots);
+            if(n <= 0)
+                return first;
+            head_.store(head + static_cast<unsigned>(n), X);
+        }
+        else {
+            int const length = n;
+            do {
+                int const slots = static_cast<int>(tail_.load(X) + downcast().size_ - head);
+                n = std::min(length, slots);
+                if(n <= 0)
+                    return first;
+            } while(ATOMIC_QUEUE_UNLIKELY(!head_.compare_exchange_weak(head, head + static_cast<unsigned>(n), X, X))); // This loop is not FIFO.
+        }
+
+        do {
+            downcast().do_push(*first++, head++);
+        } while(--n);
+        return first;
+    }
+
     template<class T>
     ATOMIC_QUEUE_INLINE bool try_pop(T& element) noexcept {
         auto tail = tail_.load(X);
@@ -408,6 +436,33 @@ class AtomicQueueCommon {
         return true;
     }
 
+    template<class OutputIt>
+    ATOMIC_QUEUE_INLINE int try_pop(OutputIt& first, int n) noexcept {
+        auto tail = tail_.load(X);
+        if(Derived::spsc_) {
+            int const num_elements = static_cast<int>(head_.load(X) - tail);
+            n = std::min(n, num_elements);
+            if(n <= 0)
+                return 0;
+            tail_.store(tail + static_cast<unsigned>(n), X);
+        }
+        else {
+            int const desired_pops = n;
+            do {
+                int const num_elements = static_cast<int>(head_.load(X) - tail);
+                n = std::min(desired_pops, num_elements);
+                if(n <= 0)
+                    return 0;
+            } while(ATOMIC_QUEUE_UNLIKELY(!tail_.compare_exchange_weak(tail, tail + static_cast<unsigned>(n), X, X))); // This loop is not FIFO.
+        }
+
+        int i = n;
+        do {
+            *first++ = downcast().do_pop(tail++);
+        } while(--i);
+        return n;
+    }
+
     template<class T>
     ATOMIC_QUEUE_INLINE void push(T&& element) noexcept {
         unsigned head;
@@ -422,6 +477,24 @@ class AtomicQueueCommon {
         downcast().do_push(std::forward<T>(element), head);
     }
 
+    template<class InputIt>
+    ATOMIC_QUEUE_INLINE InputIt push(InputIt first, InputIt const last) noexcept {
+        unsigned n = static_cast<unsigned>(std::distance(first, last));
+        unsigned head;
+        if(Derived::spsc_) {
+            head = head_.load(X);
+            head_.store(head + n, X);
+        }
+        else {
+            constexpr auto memory_order = Derived::total_order_ ? std::memory_order_seq_cst : std::memory_order_relaxed;
+            head = head_.fetch_add(n, memory_order); // FIFO and total order on Intel regardless, as of 2019.
+        }
+        while(n--) {
+            downcast().do_push(*first++, head++);
+        }
+        return first;
+    }
+
     ATOMIC_QUEUE_INLINE auto pop() noexcept {
         unsigned tail;
         if(Derived::spsc_) {
@@ -435,6 +508,23 @@ class AtomicQueueCommon {
         return downcast().do_pop(tail);
     }
 
+    template<class OutputIt>
+    ATOMIC_QUEUE_INLINE OutputIt pop(OutputIt first, unsigned n) noexcept {
+        unsigned tail;
+        if(Derived::spsc_) {
+            tail = tail_.load(X);
+            tail_.store(tail + n, X);
+        }
+        else {
+            constexpr auto memory_order = Derived::total_order_ ? std::memory_order_seq_cst : std::memory_order_relaxed;
+            tail = tail_.fetch_add(n, memory_order); // FIFO and total order on Intel regardless, as of 2019.
+        }
+        while(n--) {
+            *first++ = downcast().do_pop(tail++);
+        }
+        return first;
+    }
+
     ATOMIC_QUEUE_INLINE bool was_empty() const noexcept {
         return !was_size();
     }

src/benchmarks.h

@@ -73,12 +73,28 @@ struct RetryDecorator : Queue {
             spin_loop_pause();
     }
 
+    template<class InputIt>
+    ATOMIC_QUEUE_INLINE InputIt push(InputIt first, InputIt const last) noexcept {
+        while(last != (first = this->try_push(first, last))) {
+            spin_loop_pause();
+        }
+        return first;
+    }
+
     ATOMIC_QUEUE_INLINE T pop() noexcept {
         T element;
         while(!this->try_pop(element))
             spin_loop_pause();
         return element;
     }
+
+    template<class OutputIt>
+    ATOMIC_QUEUE_INLINE OutputIt pop(OutputIt first, int n) noexcept {
+        while(n -= this->try_pop(first, n)) {
+            spin_loop_pause();
+        }
+        return first;
+    }
 };
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

src/tests.cc

@@ -14,6 +14,7 @@
 #include <cstdint>
 #include <thread>
 #include <string>
+#include <vector>
 
 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
 
@@ -25,6 +26,8 @@ enum { N_STRESS_MSG = 1000000 };
 enum { STOP_MSG = -1 };
 enum { CAPACITY = 4096 };
 
+constexpr auto BATCH_SIZES = {1, 4, 7, 12};
+
 using stress_queues = boost::mpl::list<
     AtomicQueue<unsigned, CAPACITY>,
     AtomicQueue2<unsigned, CAPACITY>,
@@ -96,6 +99,83 @@ BOOST_AUTO_TEST_CASE_TEMPLATE(stress, Queue, stress_queues) {
     BOOST_CHECK_EQUAL(result_diff, 0);
 }
 
+// Check that all (batch) push'es are ever (batch) pop'ed once with multiple producer and multiple consumers.
+BOOST_AUTO_TEST_CASE_TEMPLATE(stress_batch, Queue, stress_queues) {
+    enum {
+        PRODUCERS = Queue::is_spsc() ? 1 : 3,
+        CONSUMERS = Queue::is_spsc() ? 1 : 3
+    };
+    using T = typename Queue::value_type;
+
+    for (int const BATCH_SIZE : BATCH_SIZES) {
+        Queue q;
+        Barrier barrier;
+
+        std::thread producers[PRODUCERS];
+        for(unsigned i = 0; i < PRODUCERS; ++i)
+            producers[i] = std::thread([&q, &barrier, BATCH_SIZE]() {
+                barrier.wait();
+                for(T n = N_STRESS_MSG; n;) {
+                    // Inserting elements into local buffer before
+                    std::vector<T> buffer(BATCH_SIZE);
+                    typename std::vector<T>::iterator it = buffer.begin();
+                    while (it != buffer.end() && n) {
+                        *it++ = n--;
+                    }
+                    // Pushing them to the queue
+                    q.push(buffer.begin(), it);
+                }
+            });
+
+        uint64_t results[CONSUMERS];
+        std::thread consumers[CONSUMERS];
+        for(unsigned i = 0; i < CONSUMERS; ++i)
+            consumers[i] = std::thread([&q, &barrier, &r = results[i], BATCH_SIZE]() {
+                barrier.wait();
+                uint64_t result = 0;
+
+                // Allocating local buffer
+                std::vector<T> buffer(BATCH_SIZE);
+                {
+                    bool continue_pops = true;
+                    while (continue_pops) {
+                        // Popping into local buffer before
+                        typename std::vector<T>::iterator out_it = q.pop(buffer.begin(), BATCH_SIZE);
+                        // Accumulating the output
+                        for (typename std::vector<T>::iterator it = buffer.begin(); it != out_it; ++it) {
+                            if (*it != static_cast<T>(STOP_MSG)) {
+                                result += *it;
+                            }
+                            else {
+                                continue_pops = false;
+                            }
+                        }
+                    }
+                }
+                r = result;
+            });
+
+        barrier.release(PRODUCERS + CONSUMERS);
+        for(auto& t : producers)
+            t.join();
+        // At least (CONSUMERS - 1) * BATCH_SIZE + 1 stop messages are required due to batch pop's
+        for(int i = CONSUMERS * BATCH_SIZE; i--;)
+            q.push(STOP_MSG);
+        for(auto& t : consumers)
+            t.join();
+
+        constexpr uint64_t expected_result = (N_STRESS_MSG + 1) / 2. * N_STRESS_MSG * PRODUCERS;
+        constexpr uint64_t consumer_result_min = expected_result / CONSUMERS / 10;
+        uint64_t result = 0;
+        for(auto& r : results) {
+            BOOST_WARN_GT(r, consumer_result_min); // Make sure a consumer didn't starve. False positives are possible here.
+            result += r;
+        }
+        int64_t result_diff = result - expected_result;
+        BOOST_CHECK_EQUAL(result_diff, 0);
+    }
+}
+
 ////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
 
 namespace {