From edba43927925cf3ae5c3ec890a040d2220f8bf71 Mon Sep 17 00:00:00 2001
From: Roker <roker@pep-project.org>
Date: Thu, 18 Oct 2018 16:30:16 +0200
Subject: [PATCH] added try_pop_front() and try_pop_back(). normal pop_*() now
 blocks instead of Undefined Behavior.

---
 locked_queue.hh | 107 ++++++++++++++++++++++++++++++++++++++++--------
 1 file changed, 90 insertions(+), 17 deletions(-)

diff --git a/locked_queue.hh b/locked_queue.hh
index af93958..6f7af2b 100644
--- a/locked_queue.hh
+++ b/locked_queue.hh
@@ -4,60 +4,133 @@
 #pragma once
 
 #include <list>
+#include <condition_variable>
 #include <mutex>
 
 namespace utility
 {
-    using namespace std;
-
-    template<class T> class locked_queue
+    template<class T, void(*Deleter)(T)>
+    class locked_queue
     {
-        mutex _mtx;
-        list<T> _q;
+        typedef std::recursive_mutex     Mutex;
+        typedef std::unique_lock<Mutex>  Lock;
+        
+        Mutex  _mtx;
+        std::condition_variable_any  _cv;
+        std::list<T> _q;
 
     public:
+        ~locked_queue()
+        {
+            clear();
+        }
+
+        void clear()
+        {
+            Lock L(_mtx);
+            for(auto& element : _q)
+            {
+                Deleter(element);
+            }
+            _q.clear();
+        }
+
+        // undefined behavior when queue empty
         T& back()
         {
-            lock_guard<mutex> lg(_mtx);
+            Lock lg(_mtx);
             return _q.back();
         }
+
+        // undefined behavior when queue empty
         T& front()
         {
-            lock_guard<mutex> lg(_mtx);
+            Lock lg(_mtx);
             return _q.front();
         }
+
+        // returns a copy of the last element.
+        // blocks when queue is empty
         T pop_back()
         {
-            lock_guard<mutex> lg(_mtx);
-            T r = _q.back();
+            Lock L(_mtx);
+            _cv.wait(L, [&]{ return !_q.empty(); } );
+            T ret{std::move(_q.back())};
             _q.pop_back();
             return r;
         }
+
+        // returns a copy of the first element.
+        // blocks when queue is empty
         T pop_front()
         {
-            lock_guard<mutex> lg(_mtx);
-            T r = _q.front();
+            Lock L(_mtx);
+            _cv.wait(L, [&]{ return !_q.empty(); } );
+            T ret{std::move(_q.front())};
             _q.pop_front();
             return r;
         }
+
+
+        // returns true and set a copy of the last element and pop it from queue if there is any
+        // returns false and leaves 'out' untouched if queue is empty even after 'end_time'
+        bool try_pop_back(T& out, std::chrono::steady_clock::time_point end_time)
+        {
+            Lock L(_mtx);
+            if(! _cv.wait_until(L, end_time, [this]{ return !_q.empty(); } ) )
+            {
+                return false;
+            }
+            
+            out = std::move(_q.back());
+            _q.pop_back();
+            return true;
+        }
+
+ 
+        // returns true and set a copy of the first element and pop it from queue if there is any
+        // returns false and leaves 'out' untouched if queue is empty even after 'end_time'
+        bool try_pop_front(T& out, std::chrono::steady_clock::time_point end_time)
+        {
+            Lock L(_mtx);
+            if(! _cv.wait_until(L, end_time, [this]{ return !_q.empty(); } ) )
+            {
+                return false;
+            }
+            
+            out = std::move(_q.front());
+            _q.pop_front();
+            return true;
+        }
+
         void push_back(const T& data)
         {
-            lock_guard<mutex> lg(_mtx);
-            _q.push_back(data);
+            {
+                Lock L(_mtx);
+                _q.push_back(data);
+            }
+            _cv.notify_one();
         }
+
+
         void push_front(const T& data)
         {
-            lock_guard<mutex> lg(_mtx);
-            _q.push_front(data);
+            {
+                Lock L(_mtx);
+                _q.push_front(data);
+            }
+            _cv.notify_one();
         }
+
         size_t size()
         {
-            lock_guard<mutex> lg(_mtx);
+            Lock lg(_mtx);
             return _q.size();
         }
+
         bool empty()
         {
-            lock_guard<mutex> lg(_mtx);
+            Lock lg(_mtx);
             return _q.empty();
         }
     };