I have a C++ program which does text processing on 40k records. We developed this program in C++ because we thought it would be faster. Then I used/executed this C++ part inside my C# program using the process-execute but the problem is we feel like we lost control of the execution flow: not able to debug the C++ part. I want to integrate the C++ much more in my C# program. I googled and found that I have to generate a DLL for my C++ and then i can use it inside my C# program.
Question:
Will this slow down the execution of the C++ part?
Is there any other better alternative to integrate the C++ part inside my c# program?
You have a few options here:
Write the processing in .NET and measure the performance. If it is unacceptable try to optimize it. If it is still too slow you revert to unmanaged code. But thinking that unmanaged code will be faster and for this reason writing unmanaged code without measuring IMHO is wrong approach.
As you already wrote unmanaged code you can expose it as a dynamic link library by exporting a function that will do the processing:
extern "C" __declspec(dllexport) int DoProcessing(int);
Next you import the function in managed code:
class Program
{
[DllImport("mylibrary.dll")]
static extern int DoProcessing(int input);
static void Main()
{
int result = DoProcessing(123);
}
}
This works if the input and output of your processing is not very complex and can be easily marshaled. It will have very little overhead.
Compile the unmanaged code using C++ CLI as managed assembly and reference it directly.
Wrapping C++ code inside DLL will not slow it down in any way.
Yes there is a (slight) performance penalty for calling functions in DLL as opposed in the executable - for instance the compiler cannot inline calls. But this often is completely negligible overhead (3-5 CPU instructions)
This is probably the simplest way.
You can't tell if this will be fast enough to meet your goals without measuring. Do it the simplest way possible (wrap the existing C++ code inside a DLL) and see if it meets your performance goals. I'm guessing it probably will.
Calling native code from managed does have some overhead per each method call - if your program is heavily compute bound and will be calling the native methods many times per record, you may see a slow-down due to the interop. If your code calls the native code once to process all 40k records in bulk, the cost of doing interop will be greatly dwarfed by the actual time spent processing the records. If the records are coming from a slower storage media, such as over the network, your processing time will probably be negligible compared to the I/O time.
Try to implement it in C#.
40k records seems like a VERY low number. It may be (depending on how much processing you need to do on each record) that processing the 40k records in C# is actually faster than even spawning the process like you currently do.
Other that that compile your C app to a dll and load that in-process. That will still have some overhead, but it will be WAY smaller than spawning an additional process
I agree with AdamRalph - I do not think you gained anything but integration pains by writing this code in CPP.
BTW is CPP code managed? if it is why do not you just link it into your C# code and avoid all interop overhead
Related
I want to create a wrapper of realtime face analysis sdk located here http://face.ci2cv.net/. I want to know that when I will create its wrapper using dllImport, will it effect the speed of the library ?
Probably not significantly, but it depends on how much library interacts with managed code.
The performance of unmanaged code should not be affected by the CLR. However, calls between the CLR and unmanaged code (P/Invoke calls (CLR-to-unmanaged) and reverse P/Invoke calls (unmanaged-to-CLR)) do have some overhead, particularly around argument and return value marshaling. Passing huge structures, arrays, or strings between the two often require blitting or more complex marshaling, and both take time to process.
So, if the library spends a lot of time churning in unmanaged land without interacting with any CLR code, performance should not be impacted. If you're having to make a lot of calls in and out over a short period of time, you will likely notice a decrease in performance compared with making those same library calls in a native binary.
I have read this and this and was wondering if I use in C# functions from unmanaged C++ library via C# wrapper of this library, is there going to be any difference in performance compared with the same program, but written fully with unmanaged C++ and the C++ library? I am asking about crucial performance difference bigger then 1.5 times. Notice I am asking about the function performance of the C++ library only(in the two ways - with and without the use of C# wrapper), isolating the other code!
After edit:
I was just wondering if I want to use C++ dynamic unmanaged library(.dll) in C# and I am using wrapper - which is going to be compiled to intermediate CIL code and which is not. I guess only the wrapper is being compiled to CIL, and when C# want to use C++ function from the library it is just parsing and passing the arguments to C++ function with the use of the wrapper, so there will be maybe some delay, but not like if I write the whole library via C#. Correct me if I am mistaking please.
Of course, there is overhead involved in switching from managed to unmanaged code execution. It is very modest, takes about 12 cpu cycles. All that needs to be done is write a "cookie" on the stack so that the garbage collector can recognize that subsequent stack frames belong to unmanaged code and therefore should not be inspected for valid object references.
These cookies are strung together like a linked-list, supporting the scenario where C# code calls native code which in turn calls back into managed code. Traversed by the GC when it collects. Not as uncommon as it sounds, it happens in any GUI app for example. The Click event is a good example, triggered when the UI thread pinvokes GetMessage().
Not the only thing that needs to happen however, in any practical scenario you also pass arguments to the native function. They can require a lot more work to get marshaled into a format that the native code can understand. Arrays in particular, they'll need to get pinned if the array elements are blittable, that's still pretty cheap. Gets expensive when the entire array needs to be converted because the element is not blittable. Not always easy to recognize, a profiler is forever the proper tool to detect inefficient code.
I have a C++ executable which I need to integrate into my .NET app. The C++ exe is a specialized calculator which will be invoked very frequently during lengthy processing of some large data. For this, I need the integration to be as efficient as possible.
In term of efficiency, is there any advantage of wrapping the C++ code into a CLR .dll which I can then use directly from my .NET app over just using Process.Stat and parsing the output stream?
When you use Process.Start() it is creating a new application, allcation of memory and task scheduling is an overehead. given the fact that you are calling it many times, you should make it into a DLL and use the function. as the loaded DLL will always be in memory and run faster.
lets say that there is change in the parameter to the exe, you might not catch it soon enough, if it is packaged in a DLL then its more controlled. contracts are stronger.
Launching a separate process involves creating a lot of overhead for that process and it's threads. It also will be loaded/unloaded in memory every time. A dll could be loaded into memory once, and executed many times all on the main thread. So there is definitely efficiency to be gained by going the dll route. Whether or not it's REALLY worth it is a trade-off between how much work it is to wrap it in the dll, and how much efficiency you will truly gain.
You said that it will be called frequently. If this means thousands of times, it will probably be worth putting into a dll. But really, measurement is the only way to know for sure how much difference it will make.
So we created simple C# tcp sever for video sharing. all it does is simple and shall be done "life" - recive live video packed into container (FLV in our case) from some broadcaster and share recived stream with all subscribers (means open container and create new containers and make timestamps on container structure but not decode contents of packets in any way). We tested our server but found out that its performance is not enough for 5 incoming streamers and 10 outgoing streams. Fe found this app for porting. We will try it any way but before we try I wonder if any of you have tried such thing on any of your projects. So main question - is will C++ CLI make app faster than original C#?
No.
Writing the same code in a different language won't make any difference whatsoever; it will still compile to the same IL.
C# is not a slow language; you probably have some higher-level performance issues.
You should optimize your existing code.
Not for most code, however if the code does a lot of bit level operations maybe. Likewise if you can safely make use of unmanaged memory to reuse the load on the garbage collector.
So just doing a translation of the code to managed C++ is very unlikely to have a benefit for most code, however managed C++ may let you write some code in a more complex, (and unsafe) way that runs faster.
No- not at all. C++/CLI runs on the same .NET platform as C#, effectively preventing any speed increase purely by changing language. Native C++ on the other hand may yield some benefits, but it's best to be very careful. You're most likely to yield performance benefits from a profiler than changing language, and you should only consider changing language after extensive testing of the language and code that you have.
If you are calling some functions from a native DLL via P/Invoke approach, then at least converting those callback mechanisms to C++/Cli using IJW (It Just Works) would increase the performance a bit.
Has anyone used the Intel Math Kernel library http://software.intel.com/en-us/intel-mkl/
I am thinking of using this for Random Number generation from a C# application as we need extreme performance (1.6 trillion random numbers per day).
Also any advice on minimising the overhead of consuming functions from this c++ code in my c# Monte Carlo simulation.
Am about to download the Eval from the site and above and try and benchmark this from my c# app, any help much appreciated.
Thanks
I've developed a monte carlo/stochastic software using that utilizes the MKL and the Intel Compiler. In general, you will have to wrap the random number generation in a c++ dll. This is the easiest, as you can control name mangling and calling convention. As for minimizing overhead, the best way of going about this is to keep the simulation code completely in c++, where it probably belongs anyway, and only having the C# layer call in to get an update. The only way to minimize the interop penalty is to make fewer calls, I've found the other advice (/unsafe, etc) to be useless from a performance perspective. You can see an example of the interaction and structure of this type of program at my project's repository - Stochfit.
I don't know much / anything about this library. But if it is truly C++ code then you won't be able to call it directly from C#. C# is only capable of interacting with C++ in one of three ways
PInvoke into a C wrapper on top of the C++ lib
COM Interop
Reverse PInvoke (still need 1 or 2 above to insert the wrapper func)
If it is a large C++ code base, it may be best to create a thin C++/CLI wrapper to interact with the library. Then call that from C#.
Declare the function call as "static" (although I'm not sure this would make any difference), and make sure your benchmarking compares the DLL call with the built-in C# Random class. I'm not sure the Intel code would be much faster, but who knows?
1) The link says "it includes improved integration with Microsoft Visual Studio"
2) There's an evaluation version
Therefore, why not try it? It may very well be Intel already provided the necessary bindings. Or not. At least you won't have wasted money on useless software.
Here's a high-quality efficient random number generator in C#. This code would be more efficient calling C++. Even if your C++ code ran in zero time, you'd still have the overhead of moving from managed code to unmanaged coded and back.
Something that may or may not be obvious to you: Calls across managed and unmanaged code boundaries are slow, so if you go this route you will probably want to retrieve blocks of random numbers in large batches to amortize the calling time.
Intel has a set of examples which demonstrate calling MKL from C#
http://software.intel.com/en-us/articles/using-intel-mkl-in-your-c-program