X-Git-Url: http://plrg.eecs.uci.edu/git/?a=blobdiff_plain;f=folly%2FProducerConsumerQueue.h;h=053c0e264b649075b2d148af5dc199b83ad95b22;hb=46b709bc7780303b5fefd4bbbaf67b9f268d4865;hp=de0e3cc0a39892cde2903ad60f560de33b8809d5;hpb=c51f93205176b9bb3792a1c8bedcf5228ce669ac;p=folly.git

diff --git a/folly/ProducerConsumerQueue.h b/folly/ProducerConsumerQueue.h
index de0e3cc0..053c0e26 100644
--- a/folly/ProducerConsumerQueue.h
+++ b/folly/ProducerConsumerQueue.h
@@ -1,5 +1,5 @@
 /*
- * Copyright 2012 Facebook, Inc.
+ * Copyright 2017 Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,16 +17,15 @@
 // @author Bo Hu (bhu@fb.com)
 // @author Jordan DeLong (delong.j@fb.com)
 
-#ifndef PRODUCER_CONSUMER_QUEUE_H_
-#define PRODUCER_CONSUMER_QUEUE_H_
+#pragma once
 
 #include <atomic>
 #include <cassert>
 #include <cstdlib>
+#include <memory>
 #include <stdexcept>
 #include <type_traits>
 #include <utility>
-#include <boost/noncopyable.hpp>
 
 namespace folly {
 
@@ -35,10 +34,17 @@ namespace folly {
  * without locks.
  */
 template<class T>
-struct ProducerConsumerQueue : private boost::noncopyable {
+struct ProducerConsumerQueue {
   typedef T value_type;
 
-  // size must be >= 2
+  ProducerConsumerQueue(const ProducerConsumerQueue&) = delete;
+  ProducerConsumerQueue& operator = (const ProducerConsumerQueue&) = delete;
+
+  // size must be >= 2.
+  //
+  // Also, note that the number of usable slots in the queue at any
+  // given time is actually (size-1), so if you start with an empty queue,
+  // isFull() will return true after size-1 insertions.
   explicit ProducerConsumerQueue(uint32_t size)
     : size_(size)
     , records_(static_cast<T*>(std::malloc(sizeof(T) * size)))
@@ -55,9 +61,9 @@ struct ProducerConsumerQueue : private boost::noncopyable {
     // We need to destruct anything that may still exist in our queue.
     // (No real synchronization needed at destructor time: only one
     // thread can be doing this.)
-    if (!std::has_trivial_destructor<T>::value) {
-      int read = readIndex_;
-      int end = writeIndex_;
+    if (!std::is_trivially_destructible<T>::value) {
+      size_t read = readIndex_;
+      size_t end = writeIndex_;
       while (read != end) {
         records_[read].~T();
         if (++read == size_) {
@@ -129,30 +135,42 @@ struct ProducerConsumerQueue : private boost::noncopyable {
   }
 
   bool isEmpty() const {
-   return readIndex_.load(std::memory_order_consume) !=
-         writeIndex_.load(std::memory_order_consume);
+    return readIndex_.load(std::memory_order_acquire) ==
+        writeIndex_.load(std::memory_order_acquire);
   }
 
   bool isFull() const {
-    auto nextRecord = writeIndex_.load(std::memory_order_consume) + 1;
+    auto nextRecord = writeIndex_.load(std::memory_order_acquire) + 1;
     if (nextRecord == size_) {
       nextRecord = 0;
     }
-    if (nextRecord != readIndex_.load(std::memory_order_consume)) {
+    if (nextRecord != readIndex_.load(std::memory_order_acquire)) {
       return false;
     }
     // queue is full
     return true;
   }
 
+  // * If called by consumer, then true size may be more (because producer may
+  //   be adding items concurrently).
+  // * If called by producer, then true size may be less (because consumer may
+  //   be removing items concurrently).
+  // * It is undefined to call this from any other thread.
+  size_t sizeGuess() const {
+    int ret = writeIndex_.load(std::memory_order_acquire) -
+        readIndex_.load(std::memory_order_acquire);
+    if (ret < 0) {
+      ret += size_;
+    }
+    return ret;
+  }
+
 private:
   const uint32_t size_;
   T* const records_;
 
-  std::atomic<int> readIndex_;
-  std::atomic<int> writeIndex_;
+  std::atomic<unsigned int> readIndex_;
+  std::atomic<unsigned int> writeIndex_;
 };
 
 }
-
-#endif