--- a/CMakeLists.txt	Fri May 22 16:17:28 2015 +0200
+++ b/CMakeLists.txt	Fri May 22 17:40:10 2015 +0200
@@ -70,6 +70,7 @@
 
 set(ORTHANC_CORE_SOURCES
   Core/Cache/MemoryCache.cpp
+  Core/Cache/SharedArchive.cpp
   Core/ChunkedBuffer.cpp
   Core/Compression/BufferCompressor.cpp
   Core/Compression/ZlibCompressor.cpp

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Core/Cache/SharedArchive.cpp	Fri May 22 17:40:10 2015 +0200
@@ -0,0 +1,124 @@
+/**
+ * Orthanc - A Lightweight, RESTful DICOM Store
+ * Copyright (C) 2012-2015 Sebastien Jodogne, Medical Physics
+ * Department, University Hospital of Liege, Belgium
+ *
+ * This program is free software: you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * In addition, as a special exception, the copyright holders of this
+ * program give permission to link the code of its release with the
+ * OpenSSL project's "OpenSSL" library (or with modified versions of it
+ * that use the same license as the "OpenSSL" library), and distribute
+ * the linked executables. You must obey the GNU General Public License
+ * in all respects for all of the code used other than "OpenSSL". If you
+ * modify file(s) with this exception, you may extend this exception to
+ * your version of the file(s), but you are not obligated to do so. If
+ * you do not wish to do so, delete this exception statement from your
+ * version. If you delete this exception statement from all source files
+ * in the program, then also delete it here.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ **/
+
+
+#include "../PrecompiledHeaders.h"
+#include "SharedArchive.h"
+
+
+#include "../Uuid.h"
+
+
+namespace Orthanc
+{
+  void SharedArchive::RemoveInternal(const std::string& id)
+  {
+    Archive::iterator it = archive_.find(id);
+
+    if (it != archive_.end())
+    {
+      delete it->second;
+      archive_.erase(it);
+    }
+  }
+
+
+  SharedArchive::Accessor::Accessor(SharedArchive& that,
+                                    const std::string& id) :
+    lock_(that.mutex_)
+  {
+    Archive::iterator it = that.archive_.find(id);
+
+    if (it == that.archive_.end())
+    {
+      throw OrthancException(ErrorCode_InexistentItem);
+    }
+    else
+    {
+      that.lru_.MakeMostRecent(id);
+      item_ = it->second;
+    }
+  }
+
+
+  SharedArchive::~SharedArchive()
+  {
+    for (Archive::iterator it = archive_.begin();
+         it != archive_.end(); it++)
+    {
+      delete it->second;
+    }
+  }
+
+
+  std::string SharedArchive::Add(IDynamicObject* obj)
+  {
+    boost::mutex::scoped_lock lock(mutex_);
+
+    if (archive_.size() == maxSize_)
+    {
+      // The quota has been reached, remove the oldest element
+      std::string oldest = lru_.RemoveOldest();
+      RemoveInternal(oldest);
+    }
+
+    std::string id = Toolbox::GenerateUuid();
+    RemoveInternal(id);  // Should never be useful because of UUID
+    archive_[id] = obj;
+    lru_.Add(id);
+
+    return id;
+  }
+
+
+  void SharedArchive::Remove(const std::string& id)
+  {
+    boost::mutex::scoped_lock lock(mutex_);
+    RemoveInternal(id);      
+    lru_.Invalidate(id);
+  }
+
+
+  void SharedArchive::List(std::list<std::string>& items)
+  {
+    items.clear();
+
+    boost::mutex::scoped_lock lock(mutex_);
+
+    for (Archive::const_iterator it = archive_.begin();
+         it != archive_.end(); it++)
+    {
+      items.push_back(it->first);
+    }
+  }
+}
+
+

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Core/Cache/SharedArchive.h	Fri May 22 17:40:10 2015 +0200
@@ -0,0 +1,87 @@
+/**
+ * Orthanc - A Lightweight, RESTful DICOM Store
+ * Copyright (C) 2012-2015 Sebastien Jodogne, Medical Physics
+ * Department, University Hospital of Liege, Belgium
+ *
+ * This program is free software: you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation, either version 3 of the
+ * License, or (at your option) any later version.
+ *
+ * In addition, as a special exception, the copyright holders of this
+ * program give permission to link the code of its release with the
+ * OpenSSL project's "OpenSSL" library (or with modified versions of it
+ * that use the same license as the "OpenSSL" library), and distribute
+ * the linked executables. You must obey the GNU General Public License
+ * in all respects for all of the code used other than "OpenSSL". If you
+ * modify file(s) with this exception, you may extend this exception to
+ * your version of the file(s), but you are not obligated to do so. If
+ * you do not wish to do so, delete this exception statement from your
+ * version. If you delete this exception statement from all source files
+ * in the program, then also delete it here.
+ * 
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ **/
+
+
+#pragma once
+
+#include "LeastRecentlyUsedIndex.h"
+#include "../IDynamicObject.h"
+
+#include <map>
+#include <boost/thread.hpp>
+
+namespace Orthanc
+{
+  class SharedArchive : public boost::noncopyable
+  {
+  private:
+    typedef std::map<std::string, IDynamicObject*>  Archive;
+
+    size_t         maxSize_;
+    boost::mutex   mutex_;
+    Archive        archive_;
+    Orthanc::LeastRecentlyUsedIndex<std::string> lru_;
+
+    void RemoveInternal(const std::string& id);
+
+  public:
+    class Accessor : public boost::noncopyable
+    {
+    private:
+      boost::mutex::scoped_lock  lock_;
+      IDynamicObject*            item_;
+
+    public:
+      Accessor(SharedArchive& that,
+               const std::string& id);
+
+      IDynamicObject& GetItem() const
+      {
+        return *item_;
+      }      
+    };
+
+
+    SharedArchive(size_t maxSize) : maxSize_(maxSize)
+    {
+    }
+
+    ~SharedArchive();
+
+    std::string Add(IDynamicObject* obj);  // Takes the ownership
+
+    void Remove(const std::string& id);
+
+    void List(std::list<std::string>& items);
+  };
+}
+
+

--- a/UnitTestsSources/MemoryCacheTests.cpp	Fri May 22 16:17:28 2015 +0200
+++ b/UnitTestsSources/MemoryCacheTests.cpp	Fri May 22 17:40:10 2015 +0200
@@ -39,6 +39,7 @@
 #include <boost/lexical_cast.hpp>
 #include "../Core/IDynamicObject.h"
 #include "../Core/Cache/MemoryCache.h"
+#include "../Core/Cache/SharedArchive.h"
 
 
 TEST(LRU, Basic)
@@ -228,3 +229,66 @@
 
   ASSERT_EQ("45 42 43 47 44 42 ", provider.log_);
 }
+
+
+
+
+
+
+
+namespace
+{
+  class S : public Orthanc::IDynamicObject
+  {
+  private:
+    std::string value_;
+
+  public:
+    S(const std::string& value) : value_(value)
+    {
+    }
+
+    const std::string& GetValue() const
+    {
+      return value_;
+    }
+
+    static const std::string& Access(const Orthanc::IDynamicObject& obj)
+    {
+      return dynamic_cast<const S&>(obj).GetValue();
+    }
+  };
+}
+
+
+TEST(LRU, SharedArchive)
+{
+  std::string first, second;
+  Orthanc::SharedArchive a(3);
+  first = a.Add(new S("First item"));
+  second = a.Add(new S("Second item"));
+
+  for (int i = 1; i < 100; i++)
+  {
+    a.Add(new S("Item " + boost::lexical_cast<std::string>(i)));
+    // Continuously protect the two first items
+    try { Orthanc::SharedArchive::Accessor(a, first);  } catch (Orthanc::OrthancException&) {}
+    try { Orthanc::SharedArchive::Accessor(a, second); } catch (Orthanc::OrthancException&) {}
+  }
+
+  std::list<std::string> i;
+  a.List(i);
+
+  size_t count = 0;
+  for (std::list<std::string>::const_iterator
+         it = i.begin(); it != i.end(); it++)
+  {
+    if (*it == first ||
+        *it == second)
+    {
+      count++;
+    }
+  }
+
+  ASSERT_EQ(2, count);
+}