How to check if a Process is Running or Not

Question

I am starting a process using the below code

 QProcess* process = new QProcess(); process->start(Path);

The start method will start a third party application.

If the process is already running, I should not call process->start(Path) again.

The process pointer is private member of the class.

have you looked at the docs? There are at least 3 different ways to know if the QProcess is running. — jdi
– jdi, Commented May 2, 2012 at 22:04
@jdi - I tried QProcess functions, but it always teating as Not Running. — TimeRun Cit
– TimeRun Cit, Commented May 2, 2012 at 22:08
Be careful with the syntax above. Either make sure it's destructing by manually calling it, or do QProcess* process = new QProcess(this); instead if your class inherits from QObject. — kayleeFrye_onDeck
– kayleeFrye_onDeck, Commented Apr 20, 2016 at 4:34

jdi · Accepted Answer · 2012-05-02 22:15:08Z

12

From the docs for QProcess ...

There are at least 3 ways to check if a QProcess instance is running.

QProcess.pid() : If its running, the pid will be > 0

QProcess.state() : Check it again the ProcessState enum to see if its QProcess::NotRunning

QProcess.atEnd() : Its not running if this is true

If any of these are not working as you would expect, then you will need to post a specific case of that example.

edited May 2, 2012 at 22:15

answered May 2, 2012 at 22:09

jdi

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3 Comments

TimeRun Cit Over a year ago

Thanks jdi, I think I implemented wrongly, using the process pointer directly i checked the NotRunning enum. I will try again properly.

jdi Over a year ago

@TimeRunCit: I'm not a C++ guy but just curious... If process is a private member, and you do QProcess* process = new QProcess();, is that not shadowing it with a local scope version each time?

kayleeFrye_onDeck Over a year ago

You are correct, @jdi -- this has been vexing when dealing with multiple processes. When checking a list a pointers to a new process against any of those checks, you'll get false-positives.

Community · Accepted Answer · 2017-05-23 11:46:54Z

To complement the @jdi's answer with a real-life code example:

QString executable = "C:/Program Files/tool.exe"; QProcess *process = new QProcess(this); process->start(executable, QStringList()); // some code if ( process->state() == QProcess::NotRunning ) { // do something };

QProcess::ProcessState constants are:

Constant Value Description QProcess::NotRunning 0 The process is not running. QProcess::Starting 1 The process is starting, but the program has not yet been invoked. QProcess::Running 2 The process is running and is ready for reading and writing.

Documentation is here.

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