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.
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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.
Okay, I messed something up. I've written in C++ a DLL which I call from the managed code (C# .NET). The library works like diamonds and is blazingly fast.
My DLL uses its internal state i.e. allocates heaps of memory and uses myriad of variables which are not cleared off between the calls from .NET. Instead they stay there and C# code is aware of that (there is preprocessing and building data structures), actually this is required for performance.
So what is the problem?
I want to add multi-threading, effectively by allowing each .NET thread access his own DLL. Without storing any data between the calls it would be easy achievable with just one DLL.
But in my case, do I have to copy the *.DLL the number of times equal to the number of threads and write pInvoke wrapper for each file separately?? :O I mean [DllImport(...)] for each out of like 40 functions?
No way, there must be something more clever. Help?
Simply put you need to stop sharing variables between threads.
Your global variables are the problem. Instead you need each different thread to have its own copy of the state that persists between calls. Typically you would put this state into a structure of some sort, perhaps a struct. Then an initial call to the DLL would return a new instance of this structure. You then pass that structure back into the DLL every time you call a function that requires access to the persistent state. When you are done, call back into the DLL to deallocate the structure. You don't need to declare the structure in the managed code. You can just treat it as an opaque pointer. Use IntPtr.
Of course, perhaps you'd just be better off with a C++/CLI assembly.
In the midst of asking about manually managing CLR memory, I realized I know very little.
I'm aware that the CLR will place a 'cookie' on the stack when you exit a managed context, so that the Garbage Collector won't trample your memory space; however, in everything I've read the assumption is that you are calling some library written in C.
I want to an entire write layer of my application in C#, outside of the managed context, to manage data at a low level. Then, I want to access this layer from a managed layer.
In this case, will my Unmanaged C# code compile to IL and be run on the CLR? How does this work?
I assume this is related to the same C# database project you mentioned in the question.
It is technically possible to implement an entire write layers in C/C++ or any other language. And it is technically possible to have everything else in C#. I am currently working on an application that uses unmanaged code for some high-performance low level stuff and C# for business logic and upper level management.
However, the complexity of the task shall not be underestimated. The typical way to do this, is to design a contract that both parties can understand. The contract will be exposed to the managed language and managed language will trigger calls to the native application. If you have ever tried calling a C++ method from C# you will get the idea... Plus every call to unmanaged code has quite significant performance overhead, which may kill the whole idea of low level performance.
If you really interested in high-performance relational databases, then use single low level language.
If you want to have a naive, but fully working implementation of a database, just use C#. Don't mix these two languages unless you fully understand the complexity. See Raven DB - a document based NoSQL databases that is fully built in C# only.
Will my Unmanaged C# code compile to IL and be run on the CLR?
No, there is no such thing as unmanaged C#. C# code will be always compiled into the IL code and executed by CLR. It is the case of managed code calling unmanaged code. Unmanaged code can be implemented in several languages C/C++/Assembly etc, but CLR will have no idea of what is happening in that code.
Update from a comment. There is a tool (ngen.exe) that can compile C# directly into native architecture specific code. This tool is designed to improve performance of the managed application by removing JIT-compilation stage and putting native code directly into the executable image or library. This code, however, is still "managed" by the CLR host - memory allocation and collection, managed threading, application domains, exception handling, security and all other aspects are still controlled by the CLR. So even though C# can technically be compiled into native code, this code is not running as a standalone native image.
How does this work?
Managed code interoperate with unmanaged code. There are couple of ways to do this:
Through the code via .Net Interop. This is relatively fast but looks a bit ugly in code (plus it is hard to maintain/test) (good article with C#/C/Assembly samples)
A much much slower approach, but more open to other languages: web wervices (SOAP, WS, REST and company), queueing (such as MSMQ, NServiceBus and others), also (possibly) interprocess communication. So unmanaged process sits on one end and a managed application sits on the other one.
I know this is a C# question, but if you are comfortable with C++, C++/CLI might be an option worth considering.
It allows you to selectively compile portions of your C++ code to either a managed or an unmanaged context - However be aware that code that interacts with CLR types MUST run in a managed context.
I'm not aware of the runtime cost of transitioning from managed-context to unmanaged-context and viceversa from within the C++ code, but I assume it must be similar to the cost of calling a native method via .net Interop from C#, which as #oleksii already pointed out, is expensive. In my experience this has really paid off if you need to interact frequently with native C or C++ libraries - IMHO it is much easier to call them from within a C++/CLI project rather than writing the required .net Interop interfaces in C#.
See this question for a litte bit of information on how it is done.
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.
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