I want to know about unmanaged resources.
Can anyone please give me a basic idea?
Managed resources basically means "managed memory" that is managed by the garbage collector. When you no longer have any references to a managed object (which uses managed memory), the garbage collector will (eventually) release that memory for you.
Unmanaged resources are then everything that the garbage collector does not know about. For example:
Open files
Open network connections
Unmanaged memory
In XNA: vertex buffers, index buffers, textures, etc.
Normally you want to release those unmanaged resources before you lose all the references you have to the object managing them. You do this by calling Dispose on that object, or (in C#) using the using statement which will handle calling Dispose for you.
If you neglect to Dispose of your unmanaged resources correctly, the garbage collector will eventually handle it for you when the object containing that resource is garbage collected (this is "finalization"). But because the garbage collector doesn't know about the unmanaged resources, it can't tell how badly it needs to release them - so it's possible for your program to perform poorly or run out of resources entirely.
If you implement a class yourself that handles unmanaged resources, it is up to you to implement Dispose and Finalize correctly.
Some users rank open files, db connections, allocated memory, bitmaps, file streams etc. among managed resources, others among unmanaged. So are they managed or unmanaged?
My opinion is, that the response is more complex: When you open file in .NET, you probably use some built-in .NET class System.IO.File, FileStream or something else. Because it is a normal .NET class, it is managed. But it is a wrapper, which inside does the "dirty work" (communicates with the operating system using Win32 dlls, calling low level functions or even assembler instructions) which really open the file. And this is, what .NET doesn't know about, unmanaged.
But you perhaps can open the file by yourself using assembler instructions and bypass .NET file functions. Then the handle and the open file are unmanaged resources.
The same with the DB: If you use some DB assembly, you have classes like DbConnection etc., they are known to .NET and managed. But they wrap the "dirty work", which is unmanaged (allocate memory on server, establish connection with it, ...).
If you don't use this wrapper class and open some network socket by yourself and communicate with your own strange database using some commands, it is unmanaged.
These wrapper classes (File, DbConnection etc.) are managed, but they inside use unmanaged resources the same way like you, if you don't use the wrappers and do the "dirty work" by yourself. And therefore these wrappers DO implement Dispose/Finalize patterns. It is their responsibility to allow programmer to release unmanaged resources when the wrapper is not needed anymore, and to release them when the wrapper is garbage collected. The wrapper will be correctly garbage collected by garbage collector, but the unmanaged resources inside will be collected by using the Dispose/Finalize pattern.
If you don't use built-in .NET or 3rd party wrapper classes and open files by some assembler instructions etc. in your class, these open files are unmanaged and you MUST implement dispose/finalise pattern. If you don't, there will be memory leak, forever locked resource etc. even when you don't use it anymore (file operation complete) or even after you application terminates.
But your responsibility is also when using these wrappers. For those, which implement dispose/finalise (you recognize them, that they implement IDisposable), implement also your dispose/finalise pattern and Dispose even these wrappers or give them signal to release their unmanaged resources. If you don't, the resources will be after some indefinite time released, but it is clean to release it immediately (close the file immediately and not leaving it open and blocked for random several minutes/hours). So in your class's Dispose method you call Dispose methods of all your used wrappers.
Unmanaged resources are those that run outside the .NET runtime (CLR)(aka non-.NET code.) For example, a call to a DLL in the Win32 API, or a call to a .dll written in C++.
An "unmanaged resource" is not a thing, but a responsibility. If an object owns an unmanaged resource, that means that (1) some entity outside it has been manipulated in a way that may cause problems if not cleaned up, and (2) the object has the information necessary to perform such cleanup and is responsible for doing it.
Although many types of unmanaged resources are very strongly associated with various type of operating-system entities (files, GDI handles, allocated memory blocks, etc.) there is no single type of entity which is shared by all of them other than the responsibility of cleanup. Typically, if an object either has a responsibility to perform cleanup, it will have a Dispose method which instructs it to carry out all cleanup for which it is responsible.
In some cases, objects will make allowances for the possibility that they might be abandoned without anyone having called Dispose first. The GC allows objects to request notification that they've been abandoned (by calling a routine called Finalize), and objects may use this notification to perform cleanup themselves.
Terms like "managed resource" and "unmanaged resource" are, unfortunately, used by different people to mean different things; frankly think it's more useful to think in terms of objects as either not having any cleanup responsibility, having cleanup responsibility that will only be taken care of if Dispose is called, or having cleanup responsibility which should be taken care of via Dispose, but which can also be taken care of by Finalize.
The basic difference between a managed and unmanaged resource is that the
garbage collector knows about all managed resources, at some point in time
the GC will come along and clean up all the memory and resources associated
with a managed object. The GC does not know about unmanaged resources, such
as files, stream and handles, so if you do not clean them up explicitly in
your code then you will end up with memory leaks and locked resources.
Stolen from here, feel free to read the entire post.
Any resource for which memory is allocated in the .NET managed heap is a Managed resource. CLR is completly aware of this sort of memory and will do everything to make sure that it doesn't go orphaned. Anything else is unmanaged. For example interoping with COM, might create objects in the proces memory space, but CLR will not take care of it. In this case the managed object that makes calls across the managed boundry should own the responsibility for anything beyond it.
Let us first understand how VB6 or C++ programs (Non Dotnet applications) used to execute.
We know that computers only understand machine level code. Machine level code is also called as native or binary code. So, when we execute a VB6 or C++ program, the respective language compiler, compiles the respective language source code into native code, which can then be understood by the underlying operating system and hardware.
Native code (Unmanaged Code) is specific (native) to the operating system on which it is generated. If you take this compiled native code and try to run on another operating system it will fail. So the problem with this style of program execution is that, it is not portable from one platform to another platform.
Let us now understand, how a .Net program executes. Using dotnet we can create different types of applications. A few of the common types of .NET applications include Web, Windows, Console and Mobile Applications. Irrespective of the type of the application, when you execute any .NET application the following happens
The .NET application gets compiled into Intermediate language (IL). IL is also referred as Common Intermediate language (CIL) and Microsoft Intermediate language (MSIL). Both .NET and non .NET applications generate an assembly. Assemblies have an extension of .DLL or .EXE. For example if you compile a windows or Console application, you get a .EXE, where as when we compile a web or Class library project we get a .DLL. The difference between a .NET and NON .NET assembly is that, DOTNET Assembly is in intermediate language format where as NON DOTNET assembly is in native code format.
NON DOTNET applications can run directly on top of the operating system, where as DOTNET applications run on top of a virtual environment called as Common Language Runtime (CLR). CLR contains a component called Just In-Time Compiler (JIT), which will convert the Intermediate language into native code which the underlying operating system can understand.
So, in .NET the application execution consists of 2 steps
1. Language compiler, compiles the Source Code into Intermediate Language (IL)
2. JIT compiler in CLR converts, the IL into native code which can then be run on the underlying operating system.
Since, a .NET assembly is in Intermedaite Language format and not native code, .NET assemblies are portable to any platform, as long as the target platform has the Common Language Runtime (CLR). The target platform's CLR converts the Intermedaite Language into native code that the underlying operating system can understand. Intermediate Languge is also called as managed code. This is because CLR manages the code that runs inside it. For example, in a VB6 program, the developer is responsible for de-allocating the memory consumed by an object. If a programmer forgets to de-allocate memory, we may run into hard to detecct out of memory exceptions. On the other hand a .NET programmer need not worry about de-allocating the memory consumed by an object. Automatic memory management, also known as grabage collection is provided by CLR. Apart, from garbage collection, there are several other benefits provided by the CLR, which we will discuss in a later session. Since, CLR is managing and executing the Intermediate Language, it (IL) is also called as managed code.
.NET supports different programming languages like C#, VB, J#, and C++. C#, VB, and J# can only generate managed code (IL), where as C++ can generate both managed code (IL) and un-managed code (Native code).
The native code is not stored permanently anywhere, after we close the program the native code is thrown awaya. When we execute the program again, the native code gets generated again.
.NET program is similar to java program execution. In java we have byte codes and JVM (Java Virtual Machine), where as in .NET we Intermediate Language and CLR (Common Language Runtime)
This is provided from this link - He is a great tutor.
http://csharp-video-tutorials.blogspot.in/2012/07/net-program-execution-part-1.html
Unmanaged and managed resources are based on application domain.
From my understanding, unmanaged resource is everything that is used to make connection to outside of your application domain.
It could be HttpClient class that you resort to fetch data outside of your domain or a FileStream that helps you to read/write from/to a file.
we use Using block to dispose these kind of classes objects immediately after our work is done because GC in the first place care about inside the process resources not outside ones, although it will be disposed by the GC at the end.
We have a C# .NET application which binds to an unmanaged C dll.
The C dll uses CreateFileMapping() and MapViewOfFileEx() to share memory with other processes on the same machine.
MapViewOfFileEx() uses the last parameter (lpBaseAddress) and set it to 0x08000000 in our case. This is fine for all c/c++ applications if you call the initializing function in the dll early enough.
In c#, however, bigger application allocate a lot of memory before we even get the chance to call the dll's init function in the autogenerated static method Main(). (Small c# console apps work fine).
Is there a way to like preallocate the area 0x08000000 to 0x08400000 at startup of the .NET application before the automatic allocation for classes and stuff kicks in? Then it should be no problem to map the shared memory to 0x08000000 any time we like.
Restrictions:
The obvious solutions cannot be applied here.
It is not possible to use a dynamically assigned virtual address by calling MapViewOfFile as this would require heavy changes in the C dll which currently works with absolute pointers in all processes.
It is also not possible to negotiate a common base address between all processes, as they don't startup at the same time.
I have a service that's using ASP WebApi. Each http request translates to a thread that needs to do some data manipulation (possibly changing the data). The API layer is written in C# and the data manipulation is written in C++. The C# layer calls the native library and supplies a pointer to some managed buffer.
Couple of questions:
How can I make sure there are no races? is std::mutex in the native library enough in this case? (do managed threads map to native threads? will they share the same std::mutex?)
How can I make sure that the GC doesn't release the pointer to the managed buffer while the native library is manipulating it?
Do you need a shared buffer? If the buffer is only ever used on one thread, you save yourself a lot of trouble. Managed threads do not map to native threads 1:1, but I'm not sure if that has any effect on your scenario.
You need to fix the buffer, and keep it fixed the whole time the native code has a pointer to it - releasing is the least of your worries, the .NET memory is moved around all the time. This is done using the fixed block.
Fixing managed memory:
byte[] theBuffer = new byte[256];
fixed (byte* ptr = &theBuffer[0])
{
// The pointer is now fixed - the GC is prohibited from moving the memory
TheNativeFunction(ptr);
}
// Unfixed again
However, note that prohibiting the GC from moving memory around can cause you quite a bit of trouble - it can prevent heap compaction altogether in a high-throughput server, for example.
If you don't need to work with the memory in the managed environment, you can simply allocate unmanaged memory for the task, such as by using Marshal.AllocHGlobal.
I have created an application which reads a file and fetches meta data of the file. When I launch the application the private working set is around 8MB (as viewed in Task Manager). When I scan the file, the memory shoots up to 150MB and stays there. If I add additional file using the same instance of the application the memory piles on. To understand this behavior, I used a memory profiler (Red gates) which showed me the following statistics :-
Out of the 150MB of private worker set memory
Unmanaged Memory :94MB
Others Resources (string,array etc) : 30MB
This puzzles me as I am not using any un-managed code nor any Pinvoke calls. I have also tried GC.Collect() without success.
Can someone please guide me as to how I can reduce the Unmanaged memory usage of my application and what could be the possible causes for the same.
Thanks in Advance
A recent update to ANTS shows you which .NET classes your application's unmanaged memory is used by. After enabling unmanaged memory profiling in the setup screen, navigate to the class list and sort by the new 'unmanaged size' column.
Though you may not have knowingly used unmanaged memory, many .NET Framework libraries do use native resources - for example the imaging libraries.
The reason I ask is that I have an application that (among other things) calls a MATLAB .NET component whenever data is written into a specific file. The component reads the file and creates an image out of the data contained within. This works fine.
However when I am using the underlying application to additionally process a "significant" amount of data and display the processed data in table, the call to MATLAB throws an out of memory exception, but only when I am processing this large amount of data.
Is this not an indication that the MATLAB process called will rely on the available memory of the application? I guess I just don't understand how the MATLAB memory works when being called from a .NET standpoint.
(I should also note that I call clear all before every call to the MATLAB function in an attempt to "start from scratch", but it fails regardless)
COM components built by Matlab Builder NE are in-process COM servers. This means that they are DLLs which are loaded into your application memory space. This means that the MCR, which is a kind of Matlab-Virtual-Machine is in your memory space.
I believe that .NET components should behave exactly the same.
It is entirely possible, and from what you've described, even likely that the MATLAB component is making use of unmanaged memory (memory that is not managed by the .NET garbage collector.) There is very little you can do about this, apart from ensuring that you only feed it expected data in expected quantities. You may also wish to create a support ticket with MATLAB, if you believe you are using it properly.
Never used MATLAB from C#, but as much I see it uses COM components to interact with the CLR world. You load the MATLAB unmanaged DLL's into your process memory heap. And considering that for CLR process on 32 bit machines you have approximately 1.2 GB memory space, so you go out of that available space.
Some interesting description of how the load of the unmanged COM component into the managed memory done, you can find here: Memory Management Of Unmanaged Component By CLR