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External/readerwriterqueue/benchmarks/ext/1024cores/spscqueue.h

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+#include "../../../atomicops.h"
+#include <cstdlib>		// For std::size_t
+
+// From http://www.1024cores.net/home/lock-free-algorithms/queues/unbounded-spsc-queue
+// (and http://software.intel.com/en-us/articles/single-producer-single-consumer-queue)
+
+// load with 'consume' (data-dependent) memory ordering 
+template<typename T> 
+T load_consume(T const* addr) 
+{ 
+    // hardware fence is implicit on x86 
+    T v = *const_cast<T const volatile*>(addr); 
+    moodycamel::compiler_fence(moodycamel::memory_order_seq_cst);
+    return v; 
+} 
+
+// store with 'release' memory ordering 
+template<typename T> 
+void store_release(T* addr, T v) 
+{ 
+    // hardware fence is implicit on x86 
+    moodycamel::compiler_fence(moodycamel::memory_order_seq_cst);
+    *const_cast<T volatile*>(addr) = v; 
+} 
+
+// cache line size on modern x86 processors (in bytes) 
+size_t const cache_line_size = 64; 
+// single-producer/single-consumer queue 
+template<typename T> 
+class spsc_queue 
+{ 
+public: 
+  spsc_queue() 
+  { 
+      node* n = new node; 
+      n->next_ = 0; 
+      tail_ = head_ = first_= tail_copy_ = n; 
+  }
+
+  explicit spsc_queue(size_t prealloc)
+  {
+      node* n = new node;
+      n->next_ = 0;
+      tail_ = head_ = first_ = tail_copy_ = n;
+
+      // [CD] Not (at all) the most efficient way to pre-allocate memory, but it works
+      T dummy = T();
+      for (size_t i = 0; i != prealloc; ++i) {
+          enqueue(dummy);
+      }
+      for (size_t i = 0; i != prealloc; ++i) {
+          try_dequeue(dummy);
+      }
+  }
+
+  ~spsc_queue() 
+  { 
+      node* n = first_; 
+      do 
+      { 
+          node* next = n->next_; 
+          delete n; 
+          n = next; 
+      } 
+      while (n); 
+  } 
+
+  void enqueue(T v) 
+  { 
+      node* n = alloc_node(); 
+      n->next_ = 0; 
+      n->value_ = v; 
+      store_release(&head_->next_, n); 
+      head_ = n; 
+  } 
+
+  // returns 'false' if queue is empty 
+  bool try_dequeue(T& v) 
+  { 
+      if (load_consume(&tail_->next_)) 
+      { 
+          v = tail_->next_->value_; 
+          store_release(&tail_, tail_->next_); 
+          return true; 
+      } 
+      else 
+      { 
+          return false; 
+      } 
+  } 
+
+private: 
+  // internal node structure 
+  struct node 
+  { 
+      node* next_; 
+      T value_; 
+  }; 
+
+  // consumer part 
+  // accessed mainly by consumer, infrequently be producer 
+  node* tail_; // tail of the queue 
+
+  // delimiter between consumer part and producer part, 
+  // so that they situated on different cache lines 
+  char cache_line_pad_ [cache_line_size]; 
+
+  // producer part 
+  // accessed only by producer 
+  node* head_; // head of the queue 
+  node* first_; // last unused node (tail of node cache) 
+  node* tail_copy_; // helper (points somewhere between first_ and tail_) 
+
+  node* alloc_node() 
+  { 
+      // first tries to allocate node from internal node cache, 
+      // if attempt fails, allocates node via ::operator new() 
+
+      if (first_ != tail_copy_) 
+      { 
+          node* n = first_; 
+          first_ = first_->next_; 
+          return n; 
+      } 
+      tail_copy_ = load_consume(&tail_); 
+      if (first_ != tail_copy_) 
+      { 
+          node* n = first_; 
+          first_ = first_->next_; 
+          return n; 
+      } 
+      node* n = new node; 
+      return n; 
+  } 
+
+  spsc_queue(spsc_queue const&); 
+  spsc_queue& operator = (spsc_queue const&); 
+
+};