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    <p>I believe TPL will usually use one thread per core unless you specifically tell it to use more. It's <em>possible</em> that it will detect when that's not enough - e.g. in your case, where your tasks are going to spend most of their time waiting for data.</p> <p>Is there any reason you can't use asynchronous web fetching? I suspect there's no need to have a thread per task or even a thread per core here. TPL makes various aspects of asynchronous programming easier, with things like continuations.</p> <p>In terms of efficiency, is your application actually CPU bound? It sounds like you need to be getting the maximum appropriate level of parallelism at the network side - that's the bit to concentrate on, unless the calculations are really heavyweight.</p> <hr> <h1>UPDATES - NOT FROM ORIGINAL AUTHOR</h1> <p>The answer above is great as always but could be misleading as it does not have some important changes in .NET 4.0 CLR.</p> <p>As Andras says, current TPL implementation uses the thread pool hence will use as many threads as required (<strong>number of cores is irrelevant now</strong>):</p> <blockquote> <p>The Task Parallel Library (TPL) is a collection of new classes specifically designed to make it easier and more efficient to execute very fine-grained parallel workloads on modern hardware. TPL has been available separately as a CTP for some time now, and was included in the Visual Studio 2010 CTP, but in those releases it <strong>was</strong> built on its own <em>dedicated work scheduler</em>. For Beta 1 of CLR 4.0, the default <strong>scheduler for TPL will be the CLR thread pool</strong>, which allows TPL-style workloads to “play nice” with existing, QUWI-based code, and allows us to reuse much of the underlying technology in the thread pool - in particular, the thread-injection algorithm, which we will discuss in a future post.</p> </blockquote> <p>From:</p> <p><a href="http://blogs.msdn.com/b/ericeil/archive/2009/04/23/clr-4-0-threadpool-improvements-part-1.aspx" rel="noreferrer">http://blogs.msdn.com/b/ericeil/archive/2009/04/23/clr-4-0-threadpool-improvements-part-1.aspx</a></p>
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    1. CO@Jon: I believe this was the true in the CTP release of the TPL. Now I think it is not the case.
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    2. CO@andras: could you give more details about what you mean?
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    3. CO@Jon: I believe that the one thread/CPU case was true for the CTP release of the TPL (that you could use with VS2008). Now it uses the new CLR thread pool - which might or might not create more threads, depending on some heuristics.
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