Sequential execution of QProcesses

I have 5 QT processes in a slot, which invokes 5 shell scripts on linux system. I have arranged them in a sequential manner but when I had a look at logs, came to know that the processes are not running in a sequential manner. The order of execution gets change
For eg

Code:

---

void Window::slotProcess(){
 
    statusWindow->setText("Running process");
 
   /******************* STEP 1: START A NEW PROCESS 1 ***************/
    Process_1 = new QProcess(this);
    // Connet SIGNAL::STANDARD ERROR with SLOT::UPDATE ERROR, to capture std output
    qDebug() << connect(Process_1, SIGNAL(readyReadStandardError()), this, SLOT(UpdateError()));
    // Connect SIGNAL::STANDARD OUTPUT with SLOT::UPDATE OUTPUT to capture std error
    qDebug() << connect(Process_1, SIGNAL(readyReadStandardOutput()), this, SLOT(UpdateOutput()));
    Process_1->start("/home/root/scripts/script_1.sh");
 
   /******************* STEP 2: START A NEW PROCESS 2 ***************/
    Process_2 = new QProcess(this);
    // Connet SIGNAL::STANDARD ERROR with SLOT::UPDATE ERROR, to capture std output
    qDebug() << connect(Process_2, SIGNAL(readyReadStandardError()), this, SLOT(UpdateError()));
    // Connect SIGNAL::STANDARD OUTPUT with SLOT::UPDATE OUTPUT to capture std error
    qDebug() << connect(Process_2, SIGNAL(readyReadStandardOutput()), this, SLOT(UpdateOutput()));
    Process_2->start("/home/root/scripts/script_2.sh");
 
.....

---

But when I see debug messages, it shows there is no sequence in execution. How can I control the sequence of execution of my processes?
The wait for finish method will block the code, is there an alternative ?

Use QProcess::waitForFinished before starting next process.
Oops : You do not want to use a waitForFinished.

Create one master script which will call subscripts.

Lesiok's option is probably the least effort. Here are some other options:

Create a slot for each step. In the slot for step 1 start the relevant process and connect() its finished() signal to the slot for step 2... and so on. You should check the exit state of step n at the top of step n+1 before starting the new step's process.

Or, between steps:

Code:

---

QEventLoop loop;
connect(process, SIGNAL(finished(...)), &loop, SLOT(quit()));
loop.exec();

---

Quote:

---

Originally Posted by ChrisW67

Lesiok's option is probably the least effort. Here are some other options:

Create a slot for each step. In the slot for step 1 start the relevant process and connect() its finished() signal to the slot for step 2... and so on. You should check the exit state of step n at the top of step n+1 before starting the new step's process.

Or, between steps:

Code:

---

QEventLoop loop;
connect(process, SIGNAL(finished(...)), &loop, SLOT(quit()));
loop.exec();

---

---

The problem here, is you are assuming that the QProcess is still running when you start the event loop.

With the following code

Code:

---

QProcess process;
QEventLoop loop;
connect(process, SIGNAL(finished(...)), &loop, SLOT(quit()));
process.start();
loop.exec()

---

its possible for short running executables that the process ends before the loop.exec command. This has bit me in the butt more than once.

The best solution I have come up with is the following

Code:

---

QProcess process;
QEventLoop loop;
bool processFinished = false;
connect(process, &QProcess::finished, 
[&loop, &processFinished]()
{
    processFinished = true;
    if ( loop.isRunning() )
         loop.exit();
}
)
process.start();
loop.exec()

---