Fixes for EMBB-446.

containers_cpp/include/embb/containers/internal/wait_free_spsc_queue-inl.h

@@ -37,11 +37,19 @@
 namespace embb {
 namespace containers {
 template<typename Type, class Allocator>
-WaitFreeSPSCQueue<Type, Allocator>::WaitFreeSPSCQueue(size_t capacity) :
-capacity(capacity),
-  head_index(0),
-  tail_index(0) {
-  queue_array = allocator.allocate(capacity);
+size_t WaitFreeSPSCQueue<Type, Allocator>::
+AlignCapacityToPowerOfTwo(size_t capacity) {
+  size_t result = 1;
+  while (result < capacity) result <<= 1;
+  return result;
+}
+
+template<typename Type, class Allocator>
+WaitFreeSPSCQueue<Type, Allocator>::WaitFreeSPSCQueue(size_t capacity)
+    : capacity(AlignCapacityToPowerOfTwo(capacity)),
+      head_index(0),
+      tail_index(0) {
+  queue_array = allocator.allocate(this->capacity);
 }
 
 template<typename Type, class Allocator>
@@ -51,7 +59,7 @@ size_t WaitFreeSPSCQueue<Type, Allocator>::GetCapacity() {
 
 template<typename Type, class Allocator>
 bool WaitFreeSPSCQueue<Type, Allocator>::TryEnqueue(Type const & element) {
-  if (head_index - tail_index == capacity)
+  if (tail_index - head_index == capacity)
     return false;
 
   queue_array[tail_index % capacity] = element;

containers_cpp/include/embb/containers/wait_free_spsc_queue.h

@@ -145,11 +145,17 @@ class WaitFreeSPSCQueue {
    */
   embb::base::Atomic<size_t> tail_index;
 
+  /**
+   * Align capacity to the next smallest power of two
+   */
+  static size_t AlignCapacityToPowerOfTwo(size_t capacity);
+
  public:
   /**
-   * Creates a queue with the specified capacity.
+   * Creates a queue with at least the specified capacity.
    *
-   * \memory Allocates \c capacity elements of type \c Type.
+   * \memory Allocates \c 2^k elements of type \c Type, where \k is the
+   * smallest number such that <tt>capacity <= 2^k</tt> holds.
    *
    * \notthreadsafe
    *

containers_cpp/test/queue_test-inl.h

@@ -276,16 +276,43 @@ QueueTestSingleProducerSingleConsumer_ThreadMethod() {
 template<typename Queue_t, bool MultipleProducers, bool MultipleConsumers>
 void QueueTest<Queue_t, MultipleProducers, MultipleConsumers>::
 QueueTestSingleThreadEnqueueDequeue_ThreadMethod() {
+  // Enqueue the expected amount of elements
   for (int i = 0; i != n_queue_size; ++i) {
     bool success = queue->TryEnqueue(element_t(0, i * 133));
     PT_ASSERT(success == true);
   }
+
+  // Some queues may allow enqueueing more elements than their capacity
+  // permits, so try to enqueue additional elements until the queue is full
+  int oversized_count = n_queue_size;
+  while ( queue->TryEnqueue(element_t(0, oversized_count * 133)) ) {
+    ++oversized_count;
+  }
+  // Oversized amount should not be larger than the original capacity
+  PT_ASSERT_LT(oversized_count, 2 * n_queue_size);
+  
+  // Dequeue the expected amount of elements
   for (int i = 0; i != n_queue_size; ++i) {
     element_t dequ(0, -1);
     bool success = queue->TryDequeue(dequ);
     PT_ASSERT(success == true);
     PT_ASSERT(dequ.second == i * 133);
   }
+
+  // Dequeue any elements enqueued above the original capacity
+  for (int i = n_queue_size; i != oversized_count; ++i) {
+    element_t dequ(0, -1);
+    bool success = queue->TryDequeue(dequ);
+    PT_ASSERT(success == true);
+    PT_ASSERT(dequ.second == i * 133);
+  }
+
+  // Ensure the queue is now empty
+  {
+    element_t dequ;
+    bool success = queue->TryDequeue(dequ);
+    PT_ASSERT(success == false);
+  }
 }
 
 template<typename Queue_t, bool MultipleProducers, bool MultipleConsumers>