Move common utility classes to wpiutil library. (#79)

This is a breaking change to dependencies that use the static ntcore
library.  Unless the wpiutil library is also linked, linker errors will
result.  This does not affect the shared ntcore library.

wpiutil/include/support/ConcurrentQueue.h

@@ -0,0 +1,83 @@
+//
+// Copyright (c) 2013 Juan Palacios juan.palacios.puyana@gmail.com
+// Subject to the BSD 2-Clause License
+// - see < http://opensource.org/licenses/BSD-2-Clause>
+//
+
+#ifndef WPIUTIL_SUPPORT_CONCURRENT_QUEUE_H_
+#define WPIUTIL_SUPPORT_CONCURRENT_QUEUE_H_
+
+#include <queue>
+#include <thread>
+#include <mutex>
+#include <condition_variable>
+
+namespace wpi {
+
+template <typename T>
+class ConcurrentQueue {
+ public:
+  bool empty() const {
+    std::unique_lock<std::mutex> mlock(mutex_);
+    return queue_.empty();
+  }
+
+  typename std::queue<T>::size_type size() const {
+    std::unique_lock<std::mutex> mlock(mutex_);
+    return queue_.size();
+  }
+
+  T pop() {
+    std::unique_lock<std::mutex> mlock(mutex_);
+    while (queue_.empty()) {
+      cond_.wait(mlock);
+    }
+    auto item = std::move(queue_.front());
+    queue_.pop();
+    return item;
+  }
+
+  void pop(T& item) {
+    std::unique_lock<std::mutex> mlock(mutex_);
+    while (queue_.empty()) {
+      cond_.wait(mlock);
+    }
+    item = queue_.front();
+    queue_.pop();
+  }
+
+  void push(const T& item) {
+    std::unique_lock<std::mutex> mlock(mutex_);
+    queue_.push(item);
+    mlock.unlock();
+    cond_.notify_one();
+  }
+
+  void push(T&& item) {
+    std::unique_lock<std::mutex> mlock(mutex_);
+    queue_.push(std::forward<T>(item));
+    mlock.unlock();
+    cond_.notify_one();
+  }
+
+  template <typename... Args>
+  void emplace(Args&&... args) {
+    std::unique_lock<std::mutex> mlock(mutex_);
+    queue_.emplace(std::forward<Args>(args)...);
+    mlock.unlock();
+    cond_.notify_one();
+  }
+
+  ConcurrentQueue() = default;
+  ConcurrentQueue(const ConcurrentQueue&) = delete;
+  ConcurrentQueue& operator=(const ConcurrentQueue&) = delete;
+
+ private:
+  std::queue<T> queue_;
+  mutable std::mutex mutex_;
+  std::condition_variable cond_;
+};
+
+}  // namespace wpi
+
+#endif  // WPIUTIL_SUPPORT_CONCURRENT_QUEUE_H_