Re: Asyn connection/communication management with asynPortDriver

["Johnson, Andrew N. via Tech-talk" <tech-talk@aps.anl.gov>]

Hi Yann,

 

I'm not sure that I completely understand what you're asking or trying to do, but the initialization of EPICS records and device support cannot happen in the Asyn port thread. You should still be able to structure your port driver though so that it is the only place where API calls are made to the external device library.

 

The thread protection that you need for that driver doesn't necessarily mean the driver API calls all have to happen within the context of the port thread though, you may just have to create an epicsMutex for the driver and ensure that the API routines are only ever called by code that has successfully taken that mutex and releases it afterwards. That could get more complicated and my advice might be wrong if the driver is written in C++ or is multi-threaded, but the latter at least seems unlikely.

 

I'm not an expert on Asyn port threads but there are several people here who are, so please use the tech-talk list for any follow-up questions.

 

- Andrew

 

 

On 2/20/24, 9:09 AM, "Tech-talk" <tech-talk-bounces@aps.anl.gov> wrote:

Hi,

 

I would like to use the connection/communication management features of Asyn with a TCP/IP based driver using the asynPortDriver class.

I have a limitation to the underline device driver that expose the device has a non-thread-safe object , meaning it should only be access from the thread that made the API call to initiate the device handle.

 

what I want to do, is to create the device handle instance within the asyn port thread, instead of the main thread. thus, all record init and runtime operation should be performed from inside the asyn porthread.  is that possible?

my understand of asyn port drivers is still cloudy somehow. this works, but the handle is hosted by the main thread.

 

drvXXTest::drvXXTest( const char *portName, const char *interface, const char *icsCtrtype, epicsInt16 autoConnect )

        : asynPortDriver( portName,

                1, // maxAddr

                NUM_PARAMS,

                // Interface mask

                asynCommonMask | asynInt32Mask | asynUInt32DigitalMask | asynFloat64Mask | asynDrvUserMask | asynOctetMask,

                asynCommonMask | asynInt32Mask | asynUInt32DigitalMask | asynFloat64Mask | asynOctetMask,

                ASYN_CANBLOCK, // asynFlags.

                autoConnect, // Autoconnect

                0, // Default priority

                0 ), // Default stack size

{

        static const char *functionName = "drvXXTest";

 

 

        pasynManager->exceptionDisconnect( pasynUserSelf );

                // How to to call devConnect(deviceSession_, interface_) from port thread?

                // as this call run from the main one.

                asynStatus status = this->connect( pasynUserSelf );

 

                if( status ) {

                  asynPrint( pasynUserSelf, ASYN_TRACE_ERROR,

                                        "drvXXTest, error calling connect - %s\n",

                                        pasynUserSelf->errorMessage );

                }

 

        }

}

 

asynStatus drvXXTest::connect(asynUser *pasynUser) {

// devConnect instantiate the device handle and open a connection to it.

        if( !devConnect(deviceSession_, interface_) ) {

    epicsSnprintf( pasynUser->errorMessage,pasynUser->errorMessageSize,

                   "%s: Can't open %s: %s", deviceSession_, interface_, strerror( errno ) );

    return asynError;

        }

        pasynManager->exceptionConnect( pasynUser );

 

        return asynSuccess;

 

}

 

Cheers,

 

Yann