--- a/CMakeLists.txt	Fri Feb 12 15:56:37 2016 +0100
+++ b/CMakeLists.txt	Fri Feb 19 17:01:50 2016 +0100
@@ -121,6 +121,7 @@
   Core/RestApi/RestApiPath.cpp
   Core/RestApi/RestApiOutput.cpp
   Core/RestApi/RestApi.cpp
+  Core/MultiThreading/BagOfTasksProcessor.cpp
   Core/MultiThreading/Mutex.cpp
   Core/MultiThreading/ReaderWriterLock.cpp
   Core/MultiThreading/RunnableWorkersPool.cpp

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Core/MultiThreading/BagOfTasks.h	Fri Feb 19 17:01:50 2016 +0100
@@ -0,0 +1,82 @@
+/**
+ * Orthanc - A Lightweight, RESTful DICOM Store
+ * Copyright (C) 2012-2016 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 "../ICommand.h"
+
+#include <list>
+
+namespace Orthanc
+{
+  class BagOfTasks : public boost::noncopyable
+  {
+  private:
+    typedef std::list<ICommand*>  Tasks;
+
+    Tasks  tasks_;
+
+  public:
+    ~BagOfTasks()
+    {
+      for (Tasks::iterator it = tasks_.begin(); it != tasks_.end(); it++)
+      {
+        delete *it;
+      }
+    }
+
+    ICommand* Pop()
+    {
+      ICommand* task = tasks_.front();
+      tasks_.pop_front();
+      return task;
+    }
+
+    void Push(ICommand* task)   // Takes ownership
+    {
+      if (task != NULL)
+      {
+        tasks_.push_back(task);
+      }
+    }
+
+    size_t GetSize() const
+    {
+      return tasks_.size();
+    }
+
+    bool IsEmpty() const
+    {
+      return tasks_.empty();
+    }
+  };
+}

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Core/MultiThreading/BagOfTasksProcessor.cpp	Fri Feb 19 17:01:50 2016 +0100
@@ -0,0 +1,254 @@
+/**
+ * Orthanc - A Lightweight, RESTful DICOM Store
+ * Copyright (C) 2012-2016 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 "BagOfTasksProcessor.h"
+
+#include "../OrthancException.h"
+
+
+namespace Orthanc
+{
+  class BagOfTasksProcessor::Task : public IDynamicObject
+  {
+  private:
+    uint64_t                 bag_;
+    std::auto_ptr<ICommand>  command_;
+
+  public:
+    Task(uint64_t  bag,
+         ICommand* command) :
+      bag_(bag),
+      command_(command)
+    {
+    }
+
+    bool Execute()
+    {
+      try
+      {
+        return command_->Execute();
+      }
+      catch (OrthancException&)
+      {
+        return false;
+      }
+      catch (std::runtime_error&)
+      {
+        return false;
+      }
+    }
+
+    uint64_t GetBag()
+    {
+      return bag_;
+    }
+  };
+
+
+  void BagOfTasksProcessor::Worker(BagOfTasksProcessor* that)
+  {
+    while (that->continue_)
+    {
+      std::auto_ptr<IDynamicObject> obj(that->queue_.Dequeue(100));
+      if (obj.get() != NULL)
+      {
+        Task& task = *dynamic_cast<Task*>(obj.get());
+
+        {
+          boost::mutex::scoped_lock lock(that->mutex_);
+
+          Bags::iterator bag = that->bags_.find(task.GetBag());
+          assert(bag != that->bags_.end());
+          assert(bag->second.done_ < bag->second.size_);
+
+          if (bag->second.status_ != BagStatus_Running)
+          {
+            // This bag of task has failed or is tagged as canceled, do nothing
+            bag->second.done_ += 1;
+            continue;
+          }
+        }
+
+        bool success = task.Execute();
+
+        {
+          boost::mutex::scoped_lock lock(that->mutex_);
+
+          Bags::iterator bag = that->bags_.find(task.GetBag());
+          assert(bag != that->bags_.end());
+
+          if (!success)
+          {
+            bag->second.status_ = BagStatus_Failed;
+          }
+
+          assert(bag->second.done_ < bag->second.size_);
+          bag->second.done_ += 1;
+
+          if (bag->second.done_ == bag->second.size_)
+          {
+            that->exitStatus_[task.GetBag()] = (bag->second.status_ == BagStatus_Running);
+            that->bagFinished_.notify_all();
+          }
+        }
+      }
+    }
+  }
+
+
+  void BagOfTasksProcessor::Cancel(int64_t bag)
+  {
+    boost::mutex::scoped_lock  lock(mutex_);
+
+    Bags::iterator it = bags_.find(bag);
+    if (it != bags_.end())
+    {
+      it->second.status_ = BagStatus_Canceled;
+    }
+  }
+
+
+  bool BagOfTasksProcessor::Join(int64_t bag)
+  {
+    boost::mutex::scoped_lock  lock(mutex_);
+
+    while (continue_)
+    {
+      ExitStatus::iterator it = exitStatus_.find(bag);
+      if (it == exitStatus_.end())  // The bag is still running
+      {
+        bagFinished_.wait(lock);
+      }
+      else
+      {
+        bool status = it->second;
+        exitStatus_.erase(it);
+        return status;
+      }
+    }
+
+    return false;   // The processor is stopping
+  }
+
+
+  float BagOfTasksProcessor::GetProgress(int64_t bag)
+  {
+    boost::mutex::scoped_lock  lock(mutex_);
+
+    Bags::const_iterator it = bags_.find(bag);
+    if (it == bags_.end())
+    {
+      // The bag of tasks has finished
+      return 1.0f;
+    }
+    else
+    {
+      return (static_cast<float>(it->second.done_) / 
+              static_cast<float>(it->second.size_));
+    }
+  }
+
+
+  bool BagOfTasksProcessor::Handle::Join()
+  {
+    if (hasJoined_)
+    {
+      return status_;
+    }
+    else
+    {
+      status_ = that_.Join(bag_);
+      hasJoined_ = true;
+      return status_;
+    }
+  }
+
+
+  BagOfTasksProcessor::BagOfTasksProcessor(size_t countThreads) : 
+    countBags_(0),
+    continue_(true)
+  {
+    if (countThreads <= 0)
+    {
+      throw OrthancException(ErrorCode_ParameterOutOfRange);
+    }
+
+    threads_.resize(countThreads);
+
+    for (size_t i = 0; i < threads_.size(); i++)
+    {
+      threads_[i] = new boost::thread(Worker, this);
+    }
+  }
+
+
+  BagOfTasksProcessor::~BagOfTasksProcessor()
+  {
+    continue_ = false;
+
+    bagFinished_.notify_all();   // Wakes up all the pending "Join()"
+
+    for (size_t i = 0; i < threads_.size(); i++)
+    {
+      if (threads_[i])
+      {
+        if (threads_[i]->joinable())
+        {
+          threads_[i]->join();
+        }
+
+        delete threads_[i];
+        threads_[i] = NULL;
+      }
+    }
+  }
+
+
+  BagOfTasksProcessor::Handle* BagOfTasksProcessor::Submit(BagOfTasks& tasks)
+  {
+    boost::mutex::scoped_lock lock(mutex_);
+
+    uint64_t id = countBags_;
+    countBags_ += 1;
+
+    Bag bag(tasks.GetSize());
+    bags_[id] = bag;
+
+    while (!tasks.IsEmpty())
+    {
+      queue_.Enqueue(new Task(id, tasks.Pop()));
+    }
+
+    return new Handle(*this, id);
+  }
+}

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/Core/MultiThreading/BagOfTasksProcessor.h	Fri Feb 19 17:01:50 2016 +0100
@@ -0,0 +1,145 @@
+/**
+ * Orthanc - A Lightweight, RESTful DICOM Store
+ * Copyright (C) 2012-2016 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 "BagOfTasks.h"
+#include "SharedMessageQueue.h"
+
+#include <stdint.h>
+#include <map>
+
+namespace Orthanc
+{
+  class BagOfTasksProcessor : public boost::noncopyable
+  {
+  private:
+    enum BagStatus
+    {
+      BagStatus_Running,
+      BagStatus_Canceled,
+      BagStatus_Failed
+    };
+
+
+    struct Bag
+    {
+      size_t    size_;
+      size_t    done_;
+      BagStatus status_;
+
+      Bag() :
+        size_(0),
+        done_(0),
+        status_(BagStatus_Failed)
+      {
+      }
+
+      Bag(size_t size) : 
+      size_(size),
+      done_(0),
+      status_(BagStatus_Running)
+      {
+      }
+    };
+
+    class Task;
+
+
+    typedef std::map<uint64_t, Bag>   Bags;
+    typedef std::map<uint64_t, bool>  ExitStatus;
+
+    SharedMessageQueue  queue_;
+
+    boost::mutex  mutex_;
+    uint64_t  countBags_;
+    Bags bags_;
+    std::vector<boost::thread*>   threads_;
+    ExitStatus  exitStatus_;
+    bool continue_;
+
+    boost::condition_variable  bagFinished_;
+
+    static void Worker(BagOfTasksProcessor* that);
+
+    void Cancel(int64_t bag);
+
+    bool Join(int64_t bag);
+
+    float GetProgress(int64_t bag);
+
+  public:
+    class Handle : public boost::noncopyable
+    {
+      friend class BagOfTasksProcessor;
+
+    private:
+      BagOfTasksProcessor&  that_;
+      uint64_t              bag_;
+      bool                  hasJoined_;
+      bool                  status_;
+ 
+      Handle(BagOfTasksProcessor&  that,
+             uint64_t bag) : 
+        that_(that),
+        bag_(bag),
+        hasJoined_(false)
+      {
+      }
+
+    public:
+      ~Handle()
+      {
+        Join();
+      }
+
+      void Cancel()
+      {
+        that_.Cancel(bag_);
+      }
+
+      bool Join();
+
+      float GetProgress()
+      {
+        return that_.GetProgress(bag_);
+      }
+    };
+  
+
+    BagOfTasksProcessor(size_t countThreads);
+
+    ~BagOfTasksProcessor();
+
+    Handle* Submit(BagOfTasks& tasks);
+  };
+}