Experimental Physics and
Industrial Control System

Mark Rivers via Tech-talk <[email protected]> · Thu, 14 Feb 2019 17:41:33 +0000

> Well, not quite what I am looking for. A single read timeout may be cause by a device that is busy or just slow.

But if you set autoConnect=true then even though it disconnected on the read timeout, it will automatically try to reconnect on the next asyn write or read operation, so do you care that it disconnected?

I am going to set up a simple TCP device and do some experiments with disconnectOnReadTimeout, both on Linux and Windows.

Mark

-----Original Message-----
From: Dirk Zimoch <[email protected]> 
Sent: Thursday, February 14, 2019 10:11 AM
To: Mark Rivers <[email protected]>; Torsten Bögershausen <[email protected]>
Cc: [email protected]
Subject: Re: How to detect AsynIPPort disconnect?

Hi Mark, Torsten,

On 14.02.19 12:38, Torsten Bögershausen wrote:

> What happens then ?

Then the port goes to disconnect state (as shown by dbior) and the exception callback triggers. Also all further read/write commands fail.

> Later asyn versions (including 4.34) have an option 
> "disconnectOnReadTimeout"

Well, not quite what I am looking for. A single read timeout may be cause by a device that is busy or just slow.

On 14.02.19 14:14, Mark Rivers wrote:
> Hi Dirk,
> 
> 
> The problem you are seeing is due to the behavior of the behavior of recv() on your particular OS.  This is from the man page for recv():

My particular OS is Scientific Linux 6.10.

> 
> 
> ***************
> 
> RETURN VALUE
>         These calls return the number of bytes received, or -1 if an error occurred.  In the event of an error, errno is set to indicate the error.  The return value will be 0 when the peer  has  performed an orderly shutdown.
> 
> ERRORS
>         These are some standard errors generated by the socket layer.  Additional errors may be generated and returned from the underlying protocol modules; see their manual pages.
> 
>         EAGAIN or EWOULDBLOCK
>                The  socket  is marked nonblocking and the receive operation would block, or a receive timeout had been set and the timeout expired before data was received.  POSIX.1-2001 allows either error to be returned for this case, and does not require these constants to have the same value, so a portable application should check for both possibilities.
> 
> ***************
> 
> 
> For 15 minutes recv() is returning -1 with SOCKERRNO=EAGAIN, EINTR, or EWOULDBLOCK. After 15 minutes recv() finally returns 0, which according to man recv means the peer has performed an orderly shutdown.  Is this on Linux?  The last time I remember testing on Windows the time before recv() returns 0 was much shorter, 30 seconds I think.

It may as well be that for 15 minutes the SendQ of the socket fills up 
and only when it overflows I get an error.

Also the device does not perform an orderly shutdown.

With devices that shut down their socket this problem does not exist. At 
least not at this extent. The next send or recv will fail on an orderly 
shut down connection. (Unfortunately when you don't communicate, you 
don't know that the connection is closed. E.g. HTTP messages where the 
server closes the connection after sending the page are only detected 
when accessing them the next time. Hence the need for the "http" 
protocol option in drvAsynIPPortConfigure.)

In my case I simply power off the device. So the socket becomes 
unresponsive.

Would the SO_KEEPALIVE socket option be a solution (accessible via 
asynSetOption)?

Dirk

> 
> 
> As Torsten suggested, you can use asynSetOption to set the option DisconnectOnReadTimeout=Y.  That way any time a read operation times out it will disconnect the port.  This was added in asyn R4-29.
> 
> 
> 
> The following table summarizes the drvAsynIPPort driver asynSetOption keys and values.
> 
> Key     Value   Description
> disconnectOnReadTimeout N Y     Default=N. If Y then if a read operation times out the driver automatically disconnect the IP port.
> hostInfo        <host>:<port>[:localPort] [protocol]    The IP port hostInfo specification using the same syntax as drvAsynIPPortConfigure. This option allows changing at run time the Internet host and port to which this asyn port is connected. The only restriction is that the setting of the COM (TELNET RFC 2217) protocol cannot be changed from that specified with drvAsynIPPortConfigure. This is because if COM is specified in the drvAsynIPPortConfigure command then asynOctet and asynOption interpose interfaces are used, and asynManager does not support removing interpose interfaces.
> 
> In addition to these key/value pairs if the COM protocol is used then the drvAsynIPPort driver uses the same key/value pairs as the drvAsynSerialPort driver for specifying the serial parameters, i.e. "baud", "bits", etc.
> 
> 
> 
> Mark
> 
> 
> 
> ________________________________
> From: [email protected] <[email protected]> on behalf of Torsten Bögershausen via Tech-talk <[email protected]>
> Sent: Thursday, February 14, 2019 5:38 AM
> To: Dirk Zimoch
> Cc: EPICS
> Subject: Re: How to detect AsynIPPort disconnect?
> 
> 
>> Am 14.02.2019 um 11:51 schrieb Dirk Zimoch via Tech-talk <[email protected]>:
>>
>> Hello,
>>
>> I have a network device connected with drvAsynIPPort. When I switch off the device, the asyn port stays in "connected" state for about 15 minutes.
> 
> What happens then ?
>>
>> Writes to the device report no error, reads time out of course. But the port is still shown as connected. I have an exceptionCallback installed, but that is not triggered.
>>
> 
> Later asyn versions (including 4.34) have an option
> "disconnectOnReadTimeout"
> 
>> How can I make asyn find out within a reasonable time if the device is still connected?
>>
> 
> Stolen from asynRecord.c:
> 
>      case asynRecordDRTO:
>          status = pasynRecPvt->pasynOption->setOption(pasynRecPvt->asynOptionPvt,
>             pasynUser, "disconnectOnReadTimeout", drto_choices[pasynRec->drto]);
>          break;
> 
> 
>> Using asyn 4.34 and EPICS 7.0.1.
>>
>> Dirk
> 
> HTH
> 

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System