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POC# MEF: Threadsafe Export
 

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    <p>Suppose I have a <code>CarSystem</code> class, which has a collection of <code>CarParts</code> objects in it. Now I wish to write a stereo plugin to the system, and I wish the format of all plugins to be:</p> <pre><code>public interface ICarPluginMetaData { string Name {get;} string Description {get;} int Status {get; set;} } public interface ICarPlugin { void int setStatus(int newStatus); } [Export(typeof(ICarPlugin))] [ExportMetaData("Name", "Stereo")] [ExportMetaData("Description","Plays music")] [ExportMetaData("Status", 0)] public class StereoPlugin : ICarPlugin { [ICarPluginImport("FrontSpeakers")] public CarPart myFrontSpeakersPointer; [ICarPluginImport("RearSpeakers")] public CarPart myRearSpeakersPointer; [ICarPluginImport("subwoofer")] public CarPart mysubwooferPointer; [Export] public void setStatus(int newStatus) { Status = newStatus; } } </code></pre> <p>Now in my CarSystem class, I define exports, however the default behavior is to create 1 static object, and hand it to all those importing it; how would I be able to do the following:</p> <pre><code>[ExportAsThreadsafe] public CarPart FrontSpeakers [ExportAsThreadsafe] public CarPart RearSpeakers [ExportAsThreadsafe] public CarPart Subwoofer [ExportAsThreadsafe] public CarPart DashLights </code></pre> <p>so that when I create a second plugin, running on a separate thread, I get a threadsafe connection to the actual object for all plugins?</p>
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    1. CO"Thread-safe connection to object"? There is absolutely no golden hammer for threading - especially one reliable enough for Microsoft to provide as part of MEF. Using `[PartCreationPolicy(CreationPolicy.NonShared)]` would give each object a unique instance (which is 'more' thread safe if used correctly). This is going to sound rude - but it's honestly good avice: go and make an effort to learn why this won't work and you will understand enough about threading to actually use it. Simple answer - `[Import]` the objects and `lock` them as always.
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    2. COAs explicit as proposing a solution, and then suggesting I learn more why "this" wont work is, I understand the problems of making something threadsafe; my question, I suppose, didn't fully illuminate my proposed algorithm.
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    3. COThere's a collection of objects. Each object has a ConcurrencyQueue (this is already threadsafe) associated with it. When a plugin requests access to the object, it's given a copy of the object which dumps messages directly into the queue. At my leisure, I process all requests currently in the queue. The objects given to plugins are/can be in separate threads, however the queue and everything else in the CarSystem are running in one. In this manner I intend to circumvention any thread conflicts. My question was: how can I create a simple custom export provider which would allow me to do this.
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