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C++ or C#?

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Quote:
Original post by Promit
A GC is always triggered by an allocation, and so it happens in the context that attempted the allocation.

There is no garbage collecting thread. None at all.

Now, the danger is that a GC takes out a lock, so if another thread tries to perform an allocation during a GC, it will block until the GC has finished. Then again, Solaris is the only system I know where malloc doesn't take an exclusive lock on the heap. And a gen0 GC (the only kind that should happen regularly) is really fast. So in .NET an allocation risks incurring a slightly long GC that may block other threads; in native code, every allocation is guaranteed to incur a slightly long linked list traversal that may block other threads.


So you are saying a "new" has nondeterministic duration? That's bad news, for example Java programmers are used to virtually free "new". In fact Java programmers can also use an asynchronous GC. Still probably better than C++, if not for that mutex.

Could C# use multiple stacks, and proper preallocation of memory? What about on stack replacement? Does it have a protection for access into native code? Could programmer choose between fast access into native code, and safe access into native code?

And what about the memory model, did MS properly write the specification?

Of course the major slowdown in GC based languages is when one piece is swapped on the HD, and GC wants to release it at any cost. Considering windoze doesn't have too smart swapping it's bad news.

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Quote:
Original post by Raghar
So you are saying a "new" has nondeterministic duration? That's bad news, for example Java programmers are used to virtually free "new".
Yes. I know the architecture of the Java GC (it's very nearly identical to CLR) but haven't actually looked up the trigger conditions. I'll take a look some time in the next couple days.
Quote:
Still probably better than C++, if not for that mutex.
Well the C allocator's also going to execute non deterministically, and it also takes that lock. Except for pathological cases (which seem to be more prevalent in server applications), .NET's memory system performance is fantastic.
Quote:
Could C# use multiple stacks, and proper preallocation of memory? What about on stack replacement?
I don't know what you're referring to with the stacks. Nothing's stopping you from implementing object pools, however. So if you want to use pools to reduce the amount of allocations happening, go ahead. Beware, however, that your perceptions of what constitute bad memory behavior may not be accurate. The CLR Perf guys have indicated that for games, we can allocate about 500K per frame (30 MB/s) of extremely short lived objects without seeing any performance effects at all. I don't know about you, but I was absolutely amazed at how large that figure is. That gives us a lot of memory to play with. 500K/frame. Damn. I can't even figure out what I'd do with that much.
Quote:
Does it have a protection for access into native code? Could programmer choose between fast access into native code, and safe access into native code?
Code executing under the CLR must have the FullTrust permission to call into native code, but if it has been granted FullTrust, it can do whatever it wants. Marshaling costs can be dangerous, as can security checks, so depending on the complexity of the call, you usually want the native code to be a "long" operation.
Quote:
And what about the memory model, did MS properly write the specification?
I didn't read the CLI spec (that's ECMA 335) but seeing as how the compact framework uses a somewhat different GC/allocation subsystem, it stands to reason that the spec only mandates external behavior that would affect applications directly.
Quote:
Of course the major slowdown in GC based languages is when one piece is swapped on the HD, and GC wants to release it at any cost. Considering windoze doesn't have too smart swapping it's bad news.
I don't see how swapping comes into the mix. The runtime is not, to my knowledge, aware of system wide memory pressure concerns, or what's being swapped. A GC is triggered when the current managed heap for the current process is full, and if the heap is still full after the GC, then a new segment is allocated into the heap. (As a sidenote, I've seen your past comments on Windows swap behavior, and I think you're completely and utterly wrong.)

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