If you have a windows service and a windows forms application that uses the same static object, is it the same object in both applications? In other words if I update the object in the service will it also be updated in the forms application as well if both are running at the same time?
They run on different processes so they don't share the static object.
Not exaclty related with your question but threads created on the same application is a different story. They will share the static variable unless is marked with ThreadStatic attribute
No. Unless you do something specific to achieve this objects are not shared between different processes.
The simple answer to this is is that each process has its own static so no, it will not be shared between the service and desktop process.
The complicated part is that there may even be multiple instances of a static in a single process.
In Java there is one instance of the static object for each ClassLoader that loads the class. I checked for equivalent functionality in C#. I found this question on SO that suggests that there is indeed something similar to multiple classloaders in in C# (I guess actually in CLR) and though I did not find any specific reference to multiple instances of a static I am sure that would be the case.
Simply put no,
static is 'static per AppDomain' (and you could have multiple domains per process), so not even for one process is safe to assume that your static variables will be 'shared' (normally is true unless you create new domains by hand, e.g. see What is AppDomain?) - e.g. web apps typically break the 'static' singletons etc.
In other words you need to use some sort of persistence to be able to share your data in between different applications. Or use remoting, WCF to communicate over application (domain) boundaries.
I think each application runs in its own Process. I really doubt that updating a static object in Windows service have any effect on static object running as Windows forms application.
Windows service runs under system account where as a Windows forms application runs under User account.
As others have pointed out in the comments, the processes run in different memory. Each process has
its own address space.
Windows service responds to Service control Manager commands.
They are completely two different things.
Related
I'm working on one project based on the Azure Functions, and I have one static helper class with buffer (private static ConcurrentDictionary) which holds some list of items to be processed at the end of execution, the question does this buffer will be shared between the multiple running instances?
It depends.
Most commonly, multiple executions of functions will run on the same instance. meaning the same .NET process and application domain, so they will share your static dictionary.
If your Function App gets too many requests to handle on a single instance, a second instance will be created, and it won't share anything with the first instance. So, you will have 2 (and 3, 4, N if needed) dictionaries in this scenario.
Any of those instances can also disappear at any moment in time, so you can't reliably store anything in the dictionary between executions. You can do that with "best effort", e.g. to cache data.
Azure Functions don't necessarily run on the same machine each time they are invoked, which means shared memory will be volatile as a future invocation may occur on a completely new machine.
Ideally, design things to be stateless and use a technology more suited to queueing tasks for later, such as an Azure queue.
If you must keep some state, put it somewhere more permanent such as the %HOME% directory or in storage.
I essentially want to make an api for an application but I only want one instance of that dll to be running at one time.
So multiple applications also need to be able to use the DLL at the same time. As you would expect from a normal api.
However I want it to be the same instance of the dll that the different applications use. This is because of communication with hardware that I don't want to be able to overlap.
DLLs are usually loaded once per process, so if your application is guaranteed to only be running in single-instance mode, there's nothing else you have to do. Your single application instance will have only one loaded DLL.
Now, if you want to "share" a "single instance" of a DLL across applications, you will inevitably have to resort to a client-server architecture. Your DLL will have to be wrapped in a Windows Service, which would expose an HTTP (or WCF) API.
You can't do that as you intend to do. The best way to do this would be having a single process (a DLL is not a process) which receives and processes messages, and have your multiple clients use an API (this would be your DLL) that just sends messages to this process.
The intercommunication of those two processes (your single process and the clients sending or receiving the messages via your API) could be done in many ways, choose the one that suits you better (basically, any kind of client/server architecture, even if the clients and the server are running on the same hardware)
This is an XY-Problem type of question. Your actual requirement is serializing interactions with the underlying hardware, so they do not overlap. Perhaps this is what you should explicitly and specifically be asking about.
Your proposed solution is to have a DLL that is kind of an OS-wide singleton or something like that. This is actually what you are asking about; although it is still not the right approach, in my opinion. The OS is in charge of managing the lifetime of the DLL modules in each process. There are many aspects to this, but for one: most DLL instances are already being shared between every process (mostly code sections, resources and such - data, of course, is not shared by default).
To solve your actual problem, you would have to resort to multi-process synchronization techniques. In Windows, this works mostly through named kernel objects like mutexes, semaphores, events and such. Another approach would be to use IPC, as other folks have already mentioned in their respective answers, which then again would require in itself some kind of synchronization.
Maybe all this is already handled by that hardware's device driver. What would be the real scenarios in which overlapped interactions with the underlying hardware would have a negative impact on the applications that use your DLL?
To ensure you have loaded one DLL per machine, you would need to run a controlling assembly in separate AppDomain, then try creating named pipe for remoting (with IpcChannel) and claim hardware resources. IpcChannel will fail to create second time in the same environment. If you need high performance communication with your hardware, use remoting only for claiming and releasing resource by another assembly used by applications.
Mutex is one of solution for exclusive control of multiple processes.
***But Mutex will sometimes occur dead lock. Be careful if you use.
I'm working on my Window Application and i'm using some static members.
public class MyParameter
{
public static string connectionString = "...";
}
Now if I install my application on computer and open two instance of same application. Will 'connectionString' common to the two instances?? Or every instance has its connectionString ?
The variable static or not is a part of your application memory. When you open 2 instances of your application you create two distinct memory locations in the OS, so there is not any relation between those 2 variables at all.
If you want to create one (relation), you have to look on different IPC (Inter Process Communication) methods available in OS, like:
Memory Mapped Files
Named Pipes
IPC Mechanisms in C# - Usage and Best Practices
No, Each application instance are isolated from one another using AppDomain. Thus each application instance will run in a seperate AppDomain and cannot access the variables from other domain. To do communicate with different domain we need to use Remoting , WCF Service
Every instance.
Static members are allocated on a per AppDomain basis. If you were to spawn a new AppDomain from within your current one.. they would be different.
Not really sure how to ask this question because I really don't know what I'm talking about. I have two DLLs (.NET), each is an AddIn that runs in two different application processes i.e. application one loads DLL one and application two loads DLL two. I wanted these DLLs to be able to communicate while loaded. In each DLL, I know the exact class that will be instantiated by the host process and I want these two living objects in each process to be able to communicate (call methods on each other). This seems like it would be possible. Has anyone done something like this before?
Although some might say a dprecated technology .Net Remoting is suited to this kind of inter-process object instance communications on the same host.
try to specify your requirements better please... there is .NET remoting to access and consume instances of objects running in another process/machine but should be used only when required.
in general WCF can be used to communicate between applications and processes but again it depends if you only want to call methods or also and absolutely have object level IPC.
Hi everyone I want to ask all of you one question related to application domain.
In .Net appdomain acts as a security boundary and two applications can run in two different domains within same process, but when i try to run multiple instances of an exe it shows in different processes in task manager.
Why is it so?
Why does it not show in same process with different appdomains?
Also is there is a way to do this i.e. multiple windows application in different appdomain inside same process.
Appdomain is a feature of the .NET framework. When you run exe's in Windows, they are started as separate processes, no matter what they are, the Windows loader doesn't care.
Theoretically, you can run any number of apps in the same appdomain, but why would you want that, if you don't need its benefits?