diff --git a/src/interface/desktop/WidgetPreviewCanvas.cpp b/src/interface/desktop/WidgetPreviewCanvas.cpp
index 47d989a..e1463f9 100644
--- a/src/interface/desktop/WidgetPreviewCanvas.cpp
+++ b/src/interface/desktop/WidgetPreviewCanvas.cpp
@@ -12,7 +12,7 @@ WidgetPreviewCanvas::WidgetPreviewCanvas(QWidget *parent) :
     pixbuf = new QImage();
     inited = false;
 
-    startTimer(1000);
+    startTimer(500);
 }
 
 WidgetPreviewCanvas::~WidgetPreviewCanvas()
@@ -65,5 +65,6 @@ void WidgetPreviewCanvas::timerEvent(QTimerEvent *)
         }
 
         canvas->getPreview()->updateLive(this);
+        update();
     }
 }
diff --git a/src/render/software/SoftwareCanvasRenderer.cpp b/src/render/software/SoftwareCanvasRenderer.cpp
index 4007e32..4106ffd 100644
--- a/src/render/software/SoftwareCanvasRenderer.cpp
+++ b/src/render/software/SoftwareCanvasRenderer.cpp
@@ -78,8 +78,8 @@ void SoftwareCanvasRenderer::postProcess(CanvasPortion *portion, bool threaded)
 {
     // Subdivide in chunks
     int chunk_size = 32;
-    int chunks_x = portion->getWidth() / chunk_size + 1;
-    int chunks_y = portion->getHeight() / chunk_size + 1;
+    int chunks_x = (portion->getWidth() - 1) / chunk_size + 1;
+    int chunks_y = (portion->getHeight() - 1) / chunk_size + 1;
     int units = chunks_x * chunks_y;
 
     // Render chunks in parallel
diff --git a/src/system/ParallelWork.cpp b/src/system/ParallelWork.cpp
index 9fb57ef..a80bb0a 100644
--- a/src/system/ParallelWork.cpp
+++ b/src/system/ParallelWork.cpp
@@ -2,6 +2,8 @@
 
 #include "Thread.h"
 #include "System.h"
+#include "Semaphore.h"
+#include "Mutex.h"
 #include "ParallelWorker.h"
 #include <cassert>
 
@@ -27,6 +29,56 @@ private:
     void* data;
 };
 
+/**
+ * Thread sub-class to perform units of work
+ */
+class ParallelWork::ParallelThread:public Thread
+{
+public:
+    ParallelThread(ParallelWork *work):
+        Thread(), work(work), sem(0)
+    {
+        interrupted = false;
+        unit = -1;
+    }
+
+    void feedUnit(int unit)
+    {
+        this->unit = unit;
+        sem.release();
+    }
+
+    void interrupt()
+    {
+        interrupted = true;
+        sem.release();
+    }
+
+protected:
+    virtual void run() override
+    {
+        while (unit >= 0 or not interrupted)
+        {
+            // Wait for a unit (or interrupt)
+            sem.acquire();
+
+            // Process the unit
+            if (unit >= 0)
+            {
+                work->worker->processParallelUnit(unit);
+                work->returnThread(this);
+                unit = -1;
+            }
+        }
+    }
+
+private:
+    ParallelWork* work;
+    Semaphore sem;
+    int unit;
+    bool interrupted;
+};
+
 ParallelWork::ParallelWork(ParallelWorker *worker, int units)
 {
     this->units = units;
@@ -52,58 +104,12 @@ ParallelWork::~ParallelWork()
     }
 }
 
-static void* _workerThreadCallback(ParallelWork::ParallelWorkerThread* thread)
-{
-    thread->result = thread->worker->processParallelUnit(thread->unit);
-    thread->status = ParallelWork::PARALLEL_WORKER_STATUS_DONE;
-    return NULL;
-}
-
-static int _runNextWorker(ParallelWork::ParallelWorkerThread threads[], int thread_count, int unit)
-{
-    int i;
-
-    while (1)
-    {
-        for (i = 0; i < thread_count; i++)
-        {
-            ParallelWork::ParallelWorkerThread* worker = threads + i;
-            if (worker->status == ParallelWork::PARALLEL_WORKER_STATUS_VOID)
-            {
-                worker->status = ParallelWork::PARALLEL_WORKER_STATUS_RUNNING;
-                worker->result = 0;
-                worker->unit = unit;
-                worker->thread = new Thread((ThreadFunction)_workerThreadCallback);
-                worker->thread->start(worker);
-
-                return 0;
-            }
-            else if (worker->status == ParallelWork::PARALLEL_WORKER_STATUS_DONE)
-            {
-                int result = worker->result;
-
-                worker->status = ParallelWork::PARALLEL_WORKER_STATUS_RUNNING;
-                worker->result = 0;
-                worker->unit = unit;
-                worker->thread->join();
-                delete worker->thread;
-                worker->thread = new Thread((ThreadFunction)_workerThreadCallback);
-                worker->thread->start(worker);
-
-                return result;
-            }
-        }
-        Thread::timeSleepMs(50);
-    }
-}
-
 int ParallelWork::perform(int thread_count)
 {
-    int i, done, result;
+    int i, done;
     assert(not running);
 
-    result = 0;
-
+    // Get thread count
     if (thread_count <= 0)
     {
         thread_count = System::getCoreCount();
@@ -112,38 +118,65 @@ int ParallelWork::perform(int thread_count)
     {
         thread_count = PARALLEL_MAX_THREADS;
     }
+    this->thread_count = thread_count;
     running = 1;
 
-    /* Init workers */
+    // Init threads
+    semaphore = new Semaphore(thread_count);
+    mutex = new Mutex();
+    threads = new ParallelThread*[thread_count];
+    available = new ParallelThread*[thread_count];
+    available_offset = 0;
+    available_length = thread_count;
     for (i = 0; i < thread_count; i++)
     {
-        threads[i].status = PARALLEL_WORKER_STATUS_VOID;
-        threads[i].worker = worker;
+        threads[i] = available[i] = new ParallelThread(this);
+        threads[i]->start();
     }
 
-    /* Perform run */
+    // Perform all units
     for (done = 0; done < units; done++)
     {
-        if (_runNextWorker(threads, thread_count, done))
+        // Take first available thread
+        semaphore->acquire();
+        mutex->acquire();
+        ParallelThread *thread = available[available_offset];
+        available_offset++;
+        if (available_offset >= thread_count)
         {
-            result++;
+            available_offset = 0;
         }
+        available_length--;
+        mutex->release();
+
+        // Feed the unit to it
+        thread->feedUnit(done);
     }
 
-    /* Wait and clean up workers */
+    // Wait for all threads to end, then cleanup
     for (i = 0; i < thread_count; i++)
     {
-        if (threads[i].status != PARALLEL_WORKER_STATUS_VOID)
-        {
-            threads[i].thread->join();
-            delete threads[i].thread;
-            if (threads[i].result)
-            {
-                result++;
-            }
-        }
+        threads[i]->interrupt();
     }
+    for (i = 0; i < thread_count; i++)
+    {
+        threads[i]->join();
+        delete threads[i];
+    }
+    delete[] threads;
+    delete[] available;
+    delete semaphore;
+    delete mutex;
 
     running = 0;
-    return result;
+    return done;
+}
+
+void ParallelWork::returnThread(ParallelWork::ParallelThread *thread)
+{
+    mutex->acquire();
+    available[(available_offset + available_length) % thread_count] = thread;
+    available_length++;
+    semaphore->release();
+    mutex->release();
 }
diff --git a/src/system/ParallelWork.h b/src/system/ParallelWork.h
index 9f4b756..3e6d923 100644
--- a/src/system/ParallelWork.h
+++ b/src/system/ParallelWork.h
@@ -13,21 +13,11 @@ class SYSTEMSHARED_EXPORT ParallelWork
 public:
     typedef int (*ParallelUnitFunction)(ParallelWork* work, int unit, void* data);
 
-    typedef enum
-    {
-        PARALLEL_WORKER_STATUS_VOID,
-        PARALLEL_WORKER_STATUS_RUNNING,
-        PARALLEL_WORKER_STATUS_DONE
-    } ParallelWorkerStatus;
-
-    typedef struct
-    {
-        Thread* thread;
-        ParallelWorker* worker;
-        ParallelWorkerStatus status;
-        int unit;
-        int result;
-    } ParallelWorkerThread;
+    /**
+     * Obscure thread class.
+     */
+    class ParallelThread;
+    friend class ParallelThread;
 
 public:
     /**
@@ -58,11 +48,22 @@ public:
      */
     int perform(int thread_count=-1);
 
+private:
+    void returnThread(ParallelThread *thread);
+
+private:
     int units;
     int running;
     ParallelWorker *worker;
     bool worker_compat;
-    ParallelWorkerThread threads[PARALLEL_MAX_THREADS];
+
+    int thread_count;
+    Mutex* mutex;
+    Semaphore* semaphore;
+    ParallelThread** threads;
+    ParallelThread** available;
+    int available_offset;
+    int available_length;
 };
 
 }
diff --git a/src/system/Semaphore.cpp b/src/system/Semaphore.cpp
new file mode 100644
index 0000000..65ca0c7
--- /dev/null
+++ b/src/system/Semaphore.cpp
@@ -0,0 +1,6 @@
+#include "Semaphore.h"
+
+Semaphore::Semaphore(int resources):
+    QSemaphore(resources)
+{
+}
diff --git a/src/system/Semaphore.h b/src/system/Semaphore.h
new file mode 100644
index 0000000..659cee2
--- /dev/null
+++ b/src/system/Semaphore.h
@@ -0,0 +1,25 @@
+#ifndef SEMAPHORE_H
+#define SEMAPHORE_H
+
+#include "system_global.h"
+
+#include <QSemaphore>
+
+namespace paysages
+{
+namespace system
+{
+
+class Semaphore: private QSemaphore
+{
+public:
+    Semaphore(int resources);
+
+    inline void acquire() {QSemaphore::acquire();}
+    inline void release() {QSemaphore::release();}
+};
+
+}
+}
+
+#endif // SEMAPHORE_H
diff --git a/src/system/Thread.h b/src/system/Thread.h
index 699e381..5c49233 100644
--- a/src/system/Thread.h
+++ b/src/system/Thread.h
@@ -29,7 +29,7 @@ public:
      * \brief Start the thread
      * \param data User data to pass to the threaded function
      */
-    void start(void* data);
+    void start(void* data=0);
 
     /*!
      * \brief Wait for the thread to end, and collect its result.
diff --git a/src/system/system.pro b/src/system/system.pro
index 73a8234..2e2f3c1 100644
--- a/src/system/system.pro
+++ b/src/system/system.pro
@@ -26,7 +26,8 @@ SOURCES += \
     PictureWriter.cpp \
     Logs.cpp \
     ParallelPool.cpp \
-    ParallelWorker.cpp
+    ParallelWorker.cpp \
+    Semaphore.cpp
 
 HEADERS += \
     system_global.h \
@@ -42,7 +43,8 @@ HEADERS += \
     PictureWriter.h \
     Logs.h \
     ParallelPool.h \
-    ParallelWorker.h
+    ParallelWorker.h \
+    Semaphore.h
 
 unix:!symbian {
     maemo5 {
diff --git a/src/system/system_global.h b/src/system/system_global.h
index c490cdf..3b003bc 100644
--- a/src/system/system_global.h
+++ b/src/system/system_global.h
@@ -21,6 +21,7 @@ namespace system {
     class ParallelWorker;
     class Thread;
     class Mutex;
+    class Semaphore;
 }
 }
 using namespace paysages::system;