Communicate between process in C#

Question

I have a service that calls a process to create a file (the process is a winform), In my service, I want to read the file once the process creates the file, how can I communicate between my service and the process to check that the file has been created correctlly.

Process.Start(assemblyPath, xsdFileName + " " + fileName + " " + exportPDFFileName);
//here I need to make sure that the file has been created correctly
return new MemoryStream(File.ReadAllBytes(exportPDFFileName));

Thank you for your help, Bilel

Could you have the service periodically check if the file exists? — Patrick, Mar 26 '19 at 11:39
Parallel processing has nothing to do with interprocess communication. Coordinating file access isn't a communication method either. — Panagiotis Kanavos, Mar 26 '19 at 11:39
I think that this is not good for perfomances, I need something to transmit to my service once the file has been created. — Bilel Chaouadi, Mar 26 '19 at 11:41
For interprocess communication, you could consider [Named Pipes](https://learn.microsoft.com/en-us/windows/desktop/ipc/named-pipes), but it's not cross-platform as far as I'm aware. — Patrick, Mar 26 '19 at 11:42
@BilelChaouadi there are a *lot* of IPC methods. The parent process could read the output stream of the current process. You could use named pipes. TCP listeners. Sockets. SOAP services. Named mutexes. — Panagiotis Kanavos, Mar 26 '19 at 11:43
Hi. You might be inspired by this library : https://github.com/TheCodeKing/XDMessaging.Net — Larry, Mar 26 '19 at 11:44
When you say 'service' are you meaning Windows Service? If so then the service doesn't invoke a WinForms app. You can inject into a service, if it's designed that way. If the WinForms is asking the Service to write the file that makes a little more sense. Also, what you're doing is starting a process, which shouldn't be controlled or monitored from your current process the way you are intending to use it. There's a logic flaw here... Can you state step by step what you're wanting to achieve here and you might get the correct logic and answer? Otherwise, maybe it's not a service... — Michael Puckett II, Mar 26 '19 at 11:45
No it is not a windows service, it is just a class library project — Bilel Chaouadi, Mar 26 '19 at 11:51
@Panagiotis Kanavos could you please explain me how can I achieve this using TCP ? — Bilel Chaouadi, Mar 26 '19 at 11:52

Koby Douek · Answer 1 · 2019-03-26T11:48:30.013

1

A simple solution is using process.WaitForExit() to know when the process ended:

Process.Start(assemblyPath, xsdFileName + " " + fileName + " " + exportPDFFileName);
process.WaitForExit();
return new MemoryStream(File.ReadAllBytes(exportPDFFileName));

Note this will work only if you know for sure that the process actually creates the file. Otherwise, I suggest either looping with a sleep to make sure the file was created (using File.Exists(path)), or reading the process output to make sure it created the file. Read this post for this option.

edited Mar 26 '19 at 11:48

answered Mar 26 '19 at 11:40

Koby Douek

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Checking the file exists with `File.Exists(path)` would surely be sufficient. – Patrick Mar 26 '19 at 11:43
@Patrick when? How often? `File.Exists` would have to run in a loop while `WaitForExit()` would return as soon as the child process finished – Panagiotis Kanavos Mar 26 '19 at 11:44
@Patrick no if creating file is long process. – BWA Mar 26 '19 at 11:44
Do `File.Exists` _after_ `process.WaitForExit()`, obviously... – Patrick Mar 26 '19 at 11:44
Thank you for your answer but I think that it is not a good idea to use File.Exists with a loop. i need some protocol to communicate between my service and my process – Bilel Chaouadi Mar 26 '19 at 11:50

Werner · Accepted Answer · 2019-03-26T12:24:32.427

1

As already mentioned, use WaitForExit or HasExited - perhaps also investigating the process ExitCode. You could define values for ExitCode and this way signal if the file has been created etc. See this link for details.

But if you want to actually do some communication between your processes then consider using anonymous pipes.

edited Mar 26 '19 at 12:24

answered Mar 26 '19 at 12:08

Werner

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Finaly I've chosen this solution with WaitForExit and an exit code. – Bilel Chaouadi Mar 28 '19 at 08:54

score 0 · Answer 3 · answered Mar 26 '19 at 13:09

If you're looking for inter-process communication protocol to describe a "wait for an action completion" semantic, it can be implemented with named event and named mutex synchronization primitives. The simplest mechanism of using these primitives is when some process in your case parent process creates a named synchronization object and waits for the signaled state of the object:

var fileCreationEvent = new EventWaitHandle(false, EventResetMode.ManualReset, "MyGloballyVisibleEvent");
...
fileCreationEvent.WaitOne();
// read your file

and another process, child process in your case, gets an access to existing event and sets it to the signaled state once it completes the some expected action:

var fileCreationEvent = EventWaitHandle.OpenExisting("MyGloballyVisibleEvent");
...
// create file here
fileCreationEvent.Set();

This is a simplified flow which doesn't take into account some concurrency aspects such as possibility that there are multiple processes which can create/delete the target file. If these things are important the approach is pretty similar to an approach you'd apply locally inside single process. In that case a file is kind of shared state which should be protected against the race conditions and you can use named Mutex for that in the same way as named event.

Communicate between process in C#

3 Answers3