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process interview questions

Top 15 process interview questions

15962 Jobs openings for process


WAIT for "any process" to finish

Is there any built in feature in bash to wait for any process to finish? The wait command only allows one to wait for child processes to finish. I would like to know if there is any way to wait for any process to finish before proceeding in any script.

A mechanical way to do this is as follows but I would like to know if there is any built in feature in bash.

while ps -p `cat $PID_FILE` > /dev/null; do sleep 1; done

Source: (StackOverflow)

How to stop java process gracefully?

How do I stop a Java process gracefully in Linux and Windows?

When does Runtime.getRuntime().addShutdownHook get called, and when does it not?

What about finalizers, do they help here?

Can I send some sort of signal to a Java process from a shell?

I am looking for preferably portable solutions.


Source: (StackOverflow)

What is the best choice for .NET inter-process communication? [closed]

Should I use Named Pipes, or .NET Remoting to communicate with a running process on my machine?


Source: (StackOverflow)

How to determine programmatically whether a particular process is 32-bit or 64-bit

How can my C# application check whether a particular application/process (note: not the current process) is running in 32-bit or 64-bit mode?

For example, I might want to query a particular process by name, i.e, 'abc.exe', or based on the process ID number.


Source: (StackOverflow)

How do I get the path of a process in Unix / Linux

In Windows environment there is an API to obtain the path which is running a process. Is there something similar in Unix / Linux?

Or is there some other way to do that in these environments?


Source: (StackOverflow)

How to spawn a process and capture its STDOUT in .NET?

I need to spawn a child process that is a console application, and capture its output.

I wrote up the following code for a method:

string retMessage = String.Empty;
ProcessStartInfo startInfo = new ProcessStartInfo();
Process p = new Process();

startInfo.CreateNoWindow = true;
startInfo.RedirectStandardOutput = true;
startInfo.RedirectStandardInput = true;

startInfo.UseShellExecute = false;
startInfo.Arguments = command;
startInfo.FileName = exec;

p.StartInfo = startInfo;
p.Start();

p.OutputDataReceived += new DataReceivedEventHandler
(
    delegate(object sender, DataReceivedEventArgs e)
    {
        using (StreamReader output = p.StandardOutput)
        {
            retMessage = output.ReadToEnd();
        }
    }
);

p.WaitForExit();

return retMessage;

However, this does not return anything. I don't believe the OutputDataReceived event is being called back, or the WaitForExit() command may be blocking the thread so it will never callback.

Any advice?

EDIT: Looks like I was trying too hard with the callback. Doing:

return p.StandardOutput.ReadToEnd(); 

Appears to work fine.


Source: (StackOverflow)

The difference between fork(), vfork(), exec() and clone()

I was looking to find the difference between these four on Google and I expected there to be a huge amount of information on this, but there really wasn't any solid comparison between the four calls.

I set about trying to compile a kind of basic at-a-glance look at the differences between these system calls and here's what I got. Is all this information correct/am I missing anything important ?

Fork : The fork call basically makes a duplicate of the current process, identical in almost every way (not everything is copied over, for example, resource limits in some implementations but the idea is to create as close a copy as possible).

The new process (child) gets a different process ID (PID) and has the the PID of the old process (parent) as its parent PID (PPID). Because the two processes are now running exactly the same code, they can tell which is which by the return code of fork - the child gets 0, the parent gets the PID of the child. This is all, of course, assuming the fork call works - if not, no child is created and the parent gets an error code.

Vfork : The basic difference between vfork and fork is that when a new process is created with vfork(), the parent process is temporarily suspended, and the child process might borrow the parent's address space. This strange state of affairs continues until the child process either exits, or calls execve(), at which point the parent process continues.

This means that the child process of a vfork() must be careful to avoid unexpectedly modifying variables of the parent process. In particular, the child process must not return from the function containing the vfork() call, and it must not call exit() (if it needs to exit, it should use _exit(); actually, this is also true for the child of a normal fork()).

Exec : The exec call is a way to basically replace the entire current process with a new program. It loads the program into the current process space and runs it from the entry point. exec() replaces the current process with a the executable pointed by the function. Control never returns to the original program unless there is an exec() error.

Clone : Clone, as fork, creates a new process. Unlike fork, these calls allow the child process to share parts of its execution context with the calling process, such as the memory space, the table of file descriptors, and the table of signal handlers.

When the child process is created with clone, it executes the function application fn(arg). (This differs from for, where execution continues in the child from the point of the fork call.) The fn argument is a pointer to a function that is called by the child process at the beginning of its execution. The arg argument is passed to the fn function.

When the fn(arg) function application returns, the child process terminates. The integer returned by fn is the exit code for the child process. The child process may also terminate explicitly by calling exit(2) or after receiving a fatal signal.

Information gotten form :

Thanks for taking the time to read this ! :)


Source: (StackOverflow)

How to make child process die after parent exits?

Suppose I have a process which spawns exactly one child process. Now when the parent process exits for whatever reason (normally or abnormally, by kill, ^C, assert failure or anything else) I want the child process to die. How to do that correctly?


Some similar question on stackoverflow:


Some similar question on stackoverflow for Windows:


Source: (StackOverflow)

Process vs. Thread

Recently, I have been asked a question in an interview what's the difference between a process and a thread. Really, I did not know the answer. I thought for a minute and gave a very weird answer.

Threads share the same memory.. processes do not. After answering this, the interviewer gave me an evil smile and fired the following questions at me:

Q. Do you know the segments in which a program gets divided?

My answer: yep (thought it was an easy one) Stack, Data, Code, Heap

Q. So, tell me which segments share threads?

I could not answer this and ended up in saying all of them.

Please, can anybody present the correct and impressive answers for the difference between a process and a thread?


Source: (StackOverflow)

127 Return code from $?

What is the meaning of return value 127 from $? in UNIX.


Source: (StackOverflow)

How do I trim a file extension from a String in Java?

What's the most efficient way to trim the suffix in Java, like this:

title part1.txt
title part2.html
=>
title part1
title part2

Source: (StackOverflow)

Starting a background process in python

I'm trying to port a shell script to the much more readable python version. The original shell script starts several processes (utilities, monitors, etc.) in the background with "&". How can I achieve the same effect in python? I'd like these processes not to die when the python scripts complete. I am sure it's related to the concept of a daemon somehow, but I couldn't find how to do this easily.


Source: (StackOverflow)

Visual Studio "Could not copy" .... during build

I keep getting this error during the build of my VS2012 C# project

Error   41  Could not copy "obj\Debug\WeinGartner.WeinCad.exe" to
 "bin\Debug\WeinGartner.WeinCad.exe". 
 Exceeded retry count of 10. Failed.    


Error   42  Unable to copy file "obj\Debug\WeinGartner.WeinCad.exe" to
"bin\Debug\WeinGartner.WeinCad.exe". The process cannot access the file
'bin\Debug\WeinGartner.WeinCad.exe' because it is being used by another 
process.    

Now I've figured out that killing the process

Weingartner.WeinCad.vhost.exe

works (sometimes ) but this is getting on my nerves. Any way to stop this happening at all?

My debugger settings are

enter image description here enter image description here


Source: (StackOverflow)

node.js as a background service

UPDATE: Since this post has gotten a lot of attention over the years, I've listed the top solutions per platform at the bottom of this post.


Original post:

I want my node.js server to run in the background, i.e.: when I close my terminal I want my server to keep running. I've googled this and came up with this tutorial, however it doesn't work as intended. So instead of using that daemon script, I thought I just used the output redirection (the 2>&1 >> file part), but this too does not exit - I get a blank line in my terminal, like it's waiting for output/errors.

I've also tried to put the process in the background, but as soon as I close my terminal the process is killed as well.

So how can I leave it running when I shut down my local computer?


Top solutions:


Source: (StackOverflow)

How to pause / sleep thread or process in Android?

I want to make a pause between two lines of code, Let me explain a bit:

-> the user clicks a button (a card in fact) and I show it by changing the background of this button:

thisbutton.setBackgroundResource(R.drawable.icon);

-> after let's say 1 second, I need to go back to the previous state of the button by changing back its background:

thisbutton.setBackgroundResource(R.drawable.defaultcard);

-> I've tried to pause the thread between these two lines of code with:

try {
    Thread.sleep(1000);
} catch (InterruptedException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}

However, this does not work. Maybe it's the process and not the Thread that I need to pause?

I've also tried (but it doesn't work):

new Reminder(5);

With this:

public class Reminder {

Timer timer;

        public Reminder(int seconds) {
            timer = new Timer();
            timer.schedule(new RemindTask(), seconds*1000);
        }

        class RemindTask extends TimerTask {
            public void run() {
                System.out.format("Time's up!%n");
                timer.cancel(); //Terminate the timer thread
            }
        }  
    }

How can I pause/sleep the thread or process?


Source: (StackOverflow)