Help with timer and JavaScript slot.

SPlatten · 30 Dec 2021, 08:38

@kshegunov Adding this now. I've actually changed the code to add:

QThread* pobjCurrThread(QThread::currentThread());
//Create new timer
ptmrScript = new QTimer();
ptmrScript->moveToThread(pobjCurrThread);
qdbg() << "pobjCurrThread: " << pobjCurrThread;

Output:

pobjCurrThread: QThread(0x600000269c80)

I have a breakpoint in the lambda function, first line, it doesn't get triggered.

kshegunov · 30 Dec 2021, 08:40

@SPlatten said in Help with timer and JavaScript slot.:

I have a breakpoint in the lambda function, first line, it doesn't get triggered.

I don't expect it to get trigerred, but again, this is not what I wrote. Here's a reminder:

Put a breakpoint in clsMainWnd::ptmrGetTimer and confirm it gets triggered (the breakpoint).

Additionally provide its source, and finally add this to the very beginning of the mentioned function:
[snip]

SPlatten · 30 Dec 2021, 08:51

@kshegunov , here is there requested source to the function:

/**
 * @brief clsMainWnd::ptmrGetTimer
 * @param crstrID : Constant reference to ID to look-up timer
 * @return A pointer to the timer or nullptr if not found
 */
QTimer* clsMainWnd::ptmrGetTimer(const QString& crstrID) {
    mpTimers::iterator itTimer(mmpTimers.find(crstrID));
    QTimer* pTimer(nullptr);
    if ( itTimer != mmpTimers.end() ) {
        pTimer = itTimer->second;
    }
    return pTimer;
}

I put breakpoint on first line of this, it does what I expected, nullptr is returned because on the first call the timer hasn't been registered.

SPlatten · wrote on 30 Dec 2021, 08:45

@kshegunov , this is the modified source:

            QThread* pobjCurrThread(QThread::currentThread());
    //Create new timer
qdbg() << "Before Timer creation: " << pobjCurrThread;
            ptmrScript = new QTimer(pobjCurrThread);
    //Register the new timer using the supplied ID
            pAppInstance->registerTimer(ptmrScript, crstrID);
    //Add any globals to the script
            clsScriptHelper::pobjGetInstance()->addGlobals(pobjScriptEng);
    //Build up script function call
            QString strFile(slstScript[SFF_FILE_IDX])
                   ,strCall(slstScript[SSF_FUNCTION_IDX])
                   ,strScriptWithCall(strScript)
                   ,strFunc(strCall
                          + QString(clsDebugService::msccBrktOpen)
                          + QString(clsDebugService::msccBrktClose)
                          + QString(clsXMLnode::msccScriptFunctionTerminator));
             if ( strScriptWithCall.endsWith(clsXMLnode::msccScriptFunctionTerminator) != true ) {
                 strScriptWithCall += clsXMLnode::msccScriptFunctionTerminator;
             }
             strScriptWithCall += strFunc;
    //Create connection to timer and script
qdbg() << "Before QObject::connect: " << QThread::currentThread();

And the resulting output in debug:

Before Timer creation: QThread(0x60000026c140)
S000000000029E000000010940T08:43:44.084W:QObject: Cannot create children for a parent that is in a different thread.
(Parent is QThread(0x60000026c140), parent's thread is QThread(0x600000004180), current thread is QThread(0x60000026c140)
S000000000030E000000010940T08:43:44.084DL00000661F../clsScriptHelper.cpp[void clsScriptHelper::createTimer]
Before QObject::connect: QThread(0x60000026c140)

SPlatten · 30 Dec 2021, 08:59

@SPlatten , I've reduced the source to just:

            QJSEngine* pobjScriptEng(clsJSON::pobjGetScriptEng());
            QThread* pobjCurrThread(QThread::currentThread());
    //Create new timer
qdbg() << "Before Timer creation: " << pobjCurrThread;
            ptmrScript = new QTimer(pobjCurrThread);
    //Create connection to timer and script
qdbg() << "Before QObject::connect: " << QThread::currentThread();

And the output is still:

Before Timer creation: QThread(0x600000264a00)
S000000000029E000000000768T08:50:01.847W:QObject: Cannot create children for a parent that is in a different thread.
(Parent is QThread(0x600000264a00), parent's thread is QThread(0x6000000042c0), current thread is QThread(0x600000264a00)
S000000000030E000000000768T08:50:01.847DL00000661F../clsScriptHelper.cpp[void clsScriptHelper::createTimer]
Before QObject::connect: QThread(0x600000264a00)

SPlatten · wrote on 30 Dec 2021, 08:53

@kshegunov , another attempt:

            QThread* pobjCurrThread(QThread::currentThread());
    //Create new timer
qdbg() << "Before Timer creation: " << pobjCurrThread;
            ptmrScript = new QTimer;
            ptmrScript->moveToThread(pobjCurrThread);
    //Create connection to timer and script
qdbg() << "Before QObject::connect: " << QThread::currentThread();

Output:

Before Timer creation: QThread(0x600000264d00)
S000000000029E000000000717T08:52:29.017DL00000662F../clsScriptHelper.cpp[void clsScriptHelper::createTimer]
Before QObject::connect: QThread(0x600000264d00)

Not seeing any errors in the debug, but execution isn't stopping in lambda either.

kshegunov · 30 Dec 2021, 09:02

Hold your horses! You have managed to confuse me about what's modified and what goes in which function. In any case in the last piece of code; after this:

//Create new timer
qdbg() << "Before Timer creation: " << pobjCurrThread;
            ptmrScript = new QTimer(pobjCurrThread);
    //Register the new timer using the supplied ID

adding

Q_ASSERT(clsJSON::pobjGetScriptEng()->currentThread() == QThread::currentThread());

should get tripped.

PS.
This does nothing:

ptmrScript = new QTimer;
ptmrScript->moveToThread(pobjCurrThread);

SPlatten · 30 Dec 2021, 09:03

@kshegunov said in Help with timer and JavaScript slot.:

Q_ASSERT(clsJSON::pobjGetScriptEng()->currentThread() == QThread::currentThread());

I cannot call currentThread() from pobjGetScriptEng(), it returns a pointer to QJSEngine.

kshegunov · 30 Dec 2021, 09:04

@SPlatten said in Help with timer and JavaScript slot.:

I cannot call currentThread() from pobjGetScriptEng(), it returns a pointer to QJSEngine.

Correct. I meant to write:

Q_ASSERT(clsJSON::pobjGetScriptEng()->thread() == QThread::currentThread());

SPlatten · 30 Dec 2021, 09:13

@kshegunov , realised that after posting, modified output to:

qdbg() << "Script Eng Thread: " << pobjScriptEng->thread();
qdbg() << "Before Timer creation: " << pobjCurrThread;

Result is:

S000000000028E000000000784T09:03:45.243DL00000642F../clsScriptHelper.cpp[void clsScriptHelper::createTimer]
Script Eng Thread: QThread(0x60000000c0d0)
S000000000029E000000000784T09:03:45.243DL00000643F../clsScriptHelper.cpp[void clsScriptHelper::createTimer]
Before Timer creation: QThread(0x60000026f260)
S000000000030E000000000784T09:03:45.243W:QObject: Cannot create children for a parent that is in a different thread.
(Parent is clsScriptHelper(0x600000208d80), parent's thread is QThread(0x60000000c0d0), current thread is QThread(0x60000026f260)
S000000000031E000000000784T09:03:45.244DL00000664F../clsScriptHelper.cpp[void clsScriptHelper::createTimer]
Before QObject::connect: QThread(0x60000026f260)

SPlatten · 30 Dec 2021, 09:12

@kshegunov , have now changed code to:

ptmrScript = new QTimer(this);
ptmrScript->moveToThread(pobjScriptEngThread);
ptmrScript->setInterval(cuintInterval);

Output is now different:

setupForm() !!!!
S000000000028E000000000716T09:06:20.132W:QObject: Cannot create children for a parent that is in a different thread.
(Parent is clsScriptHelper(0x600000202820), parent's thread is QThread(0x600000004150), current thread is QThread(0x60000025e1c0)
S000000000029E000000000716T09:06:20.132W:QObject::startTimer: Timers cannot be started from another thread
S000000000030E000000000716T09:06:20.132DL00000688F../clsScriptHelper.cpp[void clsScriptHelper::createTimer]
Is timer active: true
S000000000031E000000000716T09:06:20.132DL00000207Fsimon2.js[void clsScriptHelper::log]
setupForm() !!!!

I will add another API function to allow the script to start the timer.

JonB · wrote on 30 Dec 2021, 09:12

@SPlatten said in Help with timer and JavaScript slot.:

Cannot create children for a parent that is in a different thread.

You still have this. Excuse my complete guesswork, but do you need to go new QTimer(); rather than new QTimer(this); to move to another thread? (I have never been sure which statement causes the error message, which you can discover by stepping over or putting in qDebug() markers.)

But if all this is beyond me and being solved by @kshegunov please ignore me --- I'm just watching the discussion :)

kshegunov · 30 Dec 2021, 09:15

Right, so now comes the million bucks question(s):

Why is clsScriptHelper::createTimer called from thread different from the one pobjScriptEng has affinity for?
Why do you need to use threads to begin with?

As for the "solution":

QMetaObject::Connection cn = QObject::connect(ptmrScript
                                                         ,&QTimer::timeout

Shall provide a context object for the execution. Looking at the body, I'd say it should be something like:

QMetaObject::Connection cn = QObject::connect(ptmrScript , &QTimer::timeout, pobjScriptEng
                                                         ,[pobjScriptEng
                                                          ,ptmrScript
                                                          ,strFile
                                                          ,strFunc
                                                          ,strScriptWithCall]() {

Also the timer should be created with the correct affinity, I assume:

ptmrScript = new QTimer(pobjScriptEng);

The original questions stand notwithstanding

PS: You have race conditions all over the place ...

SPlatten · wrote on 30 Dec 2021, 09:15

@kshegunov , createTimer is called by JavaScript:

function setupForm() {
	//Query all people	  
	xmleng.log(0, "setupForm() !!!!", cstrThis, 202);
	//Create request counter property
	xmleng.setProperty(cstrFormTest, cstrStageCtr, "0");
	//Create timer to issue SQL requests
	xmleng.createTimer("t1", 50, "simon2.js@testTimer");
	xmleng.log(0, "setupForm() !!!!", cstrThis, 207);
	xmleng.startTimer("t1");
};

SPlatten · 30 Dec 2021, 09:20

@kshegunov , I've modified my source to:

 QMetaObject::Connection cn = QObject::connect(ptmrScript
                                              ,&QTimer::timeout
                                              ,pobjScriptEng
                                              ,[pobjScriptEng
                                               ,ptmrScript
                                               ,strFile
                                               ,strFunc
                                               ,strScriptWithCall]() {

still getting:

S000000000027E000000000747T09:17:30.915DL00000202Fsimon2.js[void clsScriptHelper::log]
setupForm() !!!!
S000000000028E000000000747T09:17:30.915DL00000207Fsimon2.js[void clsScriptHelper::log]
setupForm() !!!!
S000000000029E000000000747T09:17:30.915W:QObject::startTimer: Timers cannot be started from another thread

kshegunov · 30 Dec 2021, 09:21

@SPlatten said in Help with timer and JavaScript slot.:

still getting

Did you also parent the timer to the QJSEngine?

SPlatten · 30 Dec 2021, 09:24

@kshegunov, this is how it is now:

QJSEngine* pobjScriptEng(clsJSON::pobjGetScriptEng());
QThread* pobjScriptEngThread(pobjScriptEng->thread());
//Create new timer
ptmrScript = new QTimer();
ptmrScript->moveToThread(pobjScriptEngThread);
ptmrScript->setInterval(cuintInterval);

Have just modified to:

QJSEngine* pobjScriptEng(clsJSON::pobjGetScriptEng());
QThread* pobjScriptEngThread(pobjScriptEng->thread());
//Create new timer
ptmrScript = new QTimer();
ptmrScript->setParent(pobjScriptEng);
ptmrScript->moveToThread(pobjScriptEngThread);
ptmrScript->setInterval(cuintInterval);

Output is still:

S000000000027E000000000743T09:24:17.520DL00000202Fsimon2.js[void clsScriptHelper::log]
setupForm() !!!!
S000000000028E000000000743T09:24:17.520W:QObject::setParent: Cannot set parent, new parent is in a different thread
S000000000029E000000000743T09:24:17.520DL00000207Fsimon2.js[void clsScriptHelper::log]
setupForm() !!!!

JonB · wrote on 30 Dec 2021, 09:24

@SPlatten
Perhaps not relevant, but how can you go

            ptmrScript->moveToThread(pobjScriptEngThread);
            ptmrScript->setInterval(cuintInterval);

Once moved to other thread, are you still allowed to set its interval from this (different) thread?

kshegunov · 30 Dec 2021, 09:27

Okay, I'm getting really tangled. Where is QTimer::start called? In createTimer? If so, then:

QTimer timer = new QTimer();
...
// Connect the lambda with a context object, as mentioned!
...
timer->start();

SPlatten · 30 Dec 2021, 09:30

@kshegunov , I'm trying lots of things without taking the time to think about it.