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Async and Multithreading Considerations

Some applications are multi-threaded (e.g., WPF) allowing rendering to occur separately from data manipulation routines. While this allows for faster and more responsive applications, it raises potential problems if data inside plottable objects are manipulated mid-render. For example, reducing the size of the List holding data in a scatter plot while it is rendering may result in an index exception as the graphics code attempts to iterate over all of the original points.

ScottPlot 5

This example shows how to perform a “dangerous” operation (reducing the size of a List containing plotted data) which could cause an index error if it is performed mid-render while the code that draws graphics is iterating over that data. When EnableRendering is false all render requests are skipped, so a render must be manually requested after re-enabling it.

This code sample is specific to ScottPlot 5 (details)
void MyDangerousOperation(){

    // disable new renders
    formsPlot1.Plot.RenderManager.EnableRendering = false;

    // wait for the current render to finish
    while (formsPlot1.Plot.RenderManager.IsRendering) {}

    // perform your dangerous operation

    // permit new renders
    formsPlot1.Plot.RenderManager.EnableRendering = true;

    // force the plot to redraw

Advanced users may not wish to skip render requests, but instead hang render requests while an important data operation occurs. This may be achieved by adding custom code to the PreRenderLock event handler. Code here is executed before each frame is rendered and must complete before the render proceeds. Because it is called frequently users should be careful about placing long-running tasks inside this event.

This code sample is specific to ScottPlot 5 (details)
formsPlot1.Plot.RenderManager.PreRenderLock += (s, e) =>
    // perform your dangerous operation

ScottPlot 4

In ScottPlot 4 the Plot module has a render locking system to allow data manipulation in multi-threaded environments. Calling Plot.RenderLock() will hang until the current render is complete, and it will prevent future renders from occurring. This allows the user to modify the plot however they desire. Later the user can call Plot.RenderUnlock() to permit renders to continue.

This code sample is specific to ScottPlot 4 (details)
// hang until the current render is complete and prevent future renders

/* plottables and data may be freely manipulated now */

// resume automatic rendering