I've recently run into a question like this:
If you use execlp into a function and you have some more code below, in which situation will this code be executed?
For example:
execlp("ps","ps","-u","username",(char*) NULL);
some more code below --> what does its execution depend on?
Does it depend on the exit status of the program executed by execlp? Or will it be executed anyway because execlp does its stuff independently?
Thanks in advance
The only way that would happen is if execlp itself failed. Once the new program has been exec'd, it does not matter if that program succeeds or fails--it's already too late to go back to the original program instructions.
Related
I am attempting to run a command line example from the OpenThread GitHub project on WSL and have found that the code that calls poll on STDIN doesn't seem to be working.
The code waits on a number of handles with a select call. That returns correctly when a key is pressed, but when it immediately calls poll, the function just returns 0. If I comment out the poll call and directly call read, that seems to return the correct result.
Is this a bug with WSL or does the code need to be adapted somehow to work in this environment?
It turns out, the solution was to not use POLLRDNORM, but instead use POLLIN for the poll call. Apparently, POLLRDNORM is unsupported right now.
I would like to know, how would I, in Python, be able to ignore certain/all keypresses by the user while a certain function in the program is executing? Cross platform solutions are preferred, but if that is not possible, then I need to know how to do this on Macintosh. Any help is greatly appreciated! :)
EDIT: Right now, I am processing keypresses through the turtle module's onkey() function since I did create a program using turtle. I hope this helps avoid any confusion, and again, any help is greatly appreciated! :)
You might want to modify your question to show how you're currently processing key-presses. For example is this a command-line program and you're using curses?
You could use os.uname to return the os information or sys.platform, if that isn't available. The Python documentation for sys.platform indicates that 'darwin' is returned for OSX apple machines.
If the platform is darwin then you could, in your code, ignore whatever key-presses you want to.
Edit (Update due to changed question):
If you want to ignore key-presses when a certain function is being called you could either use a lock to stop the key-press function call and your particular function being executed together.
Here is an example of using a lock, this may not run, but it should give you a rough idea of what's required.
import _thread
a_lock = _thread.allocate_lock()
def certainFunction():
with a_lock:
print("Here's the code that you don't want to execute at the same time as onSpecificKeyCall()")
def onSpecificKeyCall():
with a_lock:
print("Here's the code that you don't want to execute at the same time as certainFunction()")
Or, depending on the circumstances, when the function which you don't want interrupting with a key press is called, you could call onkey() again, with the specific key to ignore, to call to a function that doesn't do anything. When your particular function has finished, you could call onkey() again to bind the key press to the function that processes the input.
I found similar problems, maybe it will help you with your problem:
globally capture, ignore and send keyevents with python xlib, recognize fake input
How do I 'lock the keyboard' to prevent any more keypresses being sent on X11/Linux/Gnome?
https://askubuntu.com/questions/160522/python-gtk-event-ignore
When I run something in the Before hook it seems to happen after the first Given step.
Scenario: Stack Overflow Example
Given some condition
When something happens
Then something should be
Before do
puts 'hello'
end
Outputs:
Scenario: Stack Overflow Example
Given some condition
Hello
....
This happens for each step.
Is this a misunderstanding on my part or a cucumber feature? How do I run something before the given step?
Many thanks in advance.
R
I don't know the technical reason but cucumber wont print using a plain 'puts' statement until after the scenario is finished.
Try STDOUT.puts "hello" and you will see that the Before hook runs first.
I'm trying to execute a child_process synchronously in node.js (Yes, I know this is bad, I have a good reason) and retrieve any output on stdout, but I can't quite figure out how...
I found this SO post: node.js execute system command synchronously that describes how to use a library (node-ffi) to execute the command, and this works great, but the only thing I'm able to get is the process exit code. Any data the command executes is sent directly to stdout -- how do I capture this?
> run('whoami')
username
0
in otherwords, username is echo'd to stdout, the result of run is 0.
I'd much rather figure out how to read stdout
So I have a solution working, but don't exactly like it... Just posting here for reference:
I'm using the node-ffi library referenced in the other SO post. I have a function that:
takes in a given command
appends >> run-sync-output
executes it
reads run-sync-output synchronously and stores the result
deletes this tmp file
returns result
There's an obvious issue where if the user doesn't have write access to the current directory, it will fail. Plus, it's just wasted effort. :-/
I have built a node.js module that solves this exact problem. Check it out :)
exec-plan
Update
The above module solves your original problem, because it allows for the synchronous chaining of child processes. Each link in the chain gets the stdout from the previous process in the chain.
I had a similar problem and I ended up writing a node extension for this. You can check out the git repository. It's open source and free and all that good stuff !
https://github.com/aponxi/npm-execxi
ExecXI is a node extension written in C++ to execute shell commands
one by one, outputting the command's output to the console in
real-time. Optional chained, and unchained ways are present; meaning
that you can choose to stop the script after a command fails
(chained), or you can continue as if nothing has happened !
Usage instructions are in the ReadMe file. Feel free to make pull requests or submit issues!
However it doesn't return the stdout yet... Well, I just released it today. Maybe we can build on it.
Anyway, I thought it was worth to mention it. I also posted this to a similar question: node.js execute system command synchronously
Since Node version v0.11.12, there is a child_process.execSync function for this.
Other than writing code a little diferent, there's actually no reason to do anything synched.
What don't you like about this? (docs)
var exec = require('child_process').exec;
exec('whoami', function (error, username) {
console.log('stdout: %s', username);
continueWithYourCode();
});
I was wondering how someone can specify an exit code when shutting a XULRunner application.
I currently use nsIAppStartup.quit() described in MDC nsIAppStartup reference to shutdown the application, but I can't figure out how to specify a process exit code.
The application is launched from a shell script and this exit code is needed to decide if it should be restarted or not.
NOTE : Passing eRestart to the quit function is useless in my situation because restarting depends on factors external to the application (system limits etc.)
Thank you and any help would be appreciated.
A quick look at XRE_main function shows that it will only return a non-zero value in case of errors - and even then the exit code is fixed. If everything succeeds and the application shuts down normally the exit code will be 0, no way to change it. XULRunner isn't really meant to be used in shell scripts, you will have to indicate your result in some other way (e.g. by writing it to a file).