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    <p>To answer the question simply, it is entirely wrong to use 200 threads on today's hardware.</p> <p>Each thread takes up 1 MB of memory, so you're taking up 200MB of page file before you even start doing anything useful.</p> <p>By all means break your operations up into little pieces that can be safely run on any thread, but put those operations on queues and have a fixed, limited number of worker threads servicing those queues.</p> <p><strong>Update:</strong> Does wasting 200MB matter? On a 32-bit machine, it's 10% of the entire theoretical address space for a process - no further questions. On a 64-bit machine, it <em>sounds</em> like a drop in the ocean of what could be theoretically available, but in practice it's still a very big chunk (or rather, a large number of pretty big chunks) of storage being pointlessly reserved by the application, and which then has to be managed by the OS. It has the effect of surrounding each client's valuable information with lots of worthless padding, which destroys locality, defeating the OS and CPU's attempts to keep frequently accessed stuff in the fastest layers of cache.</p> <p>In any case, the memory wastage is just one part of the insanity. Unless you have 200 cores (and an OS capable of utilizing) then you don't really have 200 parallel threads. You have (say) 8 cores, each frantically switching between 25 threads. Naively you might think that as a result of this, each thread experiences the equivalent of running on a core that is 25 times slower. But it's actually much worse than that - the OS spends more time taking one thread off a core and putting another one on it ("context switching") than it does actually allowing your code to run.</p> <p>Just look at how any well-known successful design tackles this kind of problem. The CLR's thread pool (even if you're not using it) serves as a fine example. It starts off assuming just one thread per core will be sufficient. It allows more to be created, but only to ensure that badly designed parallel algorithms will eventually complete. It refuses to create more than 2 threads per second, so it effectively punishes thread-greedy algorithms by slowing them down.</p>
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    1. POMany threads or as few threads as possible?
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    1. USDaniel Earwicker
    1. USDaniel Earwicker
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    1. COIs 200MB that important nowadays? Presumably this will be on a more or less dedicated server - you don't expect to run 100 game players on your workstation without noticing.
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      1. USDavid Thornley
    2. COyup, 200MB is a lot, especially if you're trying to run other things too. Besides, the rest of the app will require memory so 200Mb wasted is 200MB less cache at the very least.
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      1. USgbjbaanb
    3. COThanks. I guess I could say this is the first time I encountered a situation where I really have to think about resources like that. I think I picked a good learning project, also because I'd love to see results from my hard work ;-)
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      1. USErik van Brakel
 

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