Re: CA connection management problem

[Andrew Johnson <anj@aps.anl.gov>]

Hi Pete/Vic,

> You cannot just set up the channel and then loop on a
>       ca_get ; 
> 	ca_pend_io

Yes you can, and in some cases that's exactly what you should be doing. 
 If you started your IOC *after* your program, your posted code would 
have called ca_context_create() multiple times without a matching call 
to ca_context_destroy(), which might explain what you saw (there were 
probably multiple active contexts which were all reporting disconnects).

I suggest you make it impossible for simple programs ever to call 
ca_context_create() after it has once returned ECA_NORMAL, and don't use 
ca_context_destroy() in them at all.

I've attached my modified version of your code which loops calling just 
ca_get() and ca_pend_io().  I can stop and start the IOC it connects to 
using either 'exit' or Control-C and the channel reconnects properly in 
both cases when I restart it.  The ca_pend_io(0) after calling 
ca_create_channel() waits forever for the channel to connect before it 
starts the loop, but you could do this other ways too.

calling ca_context_create
calling ca_create_channel
calling ca_pend_io(0)
ca_pend_io returned 0x1: value=0x6
ca_pend_io returned 0x1: value=0x8
ca_pend_io returned 0x1: value=0x0
CA.Client.Exception...............................................
    Warning: "Virtual circuit disconnect"
    Context: "tux.aps.anl.gov:5064"
    Source File: ../cac.cpp line 1127
    Current Time: Fri Jan 18 2008 09:15:33.826129157
..................................................................
CA.Client.Exception...............................................
    Warning: "Virtual circuit disconnect"
    Context: "op=0, channel=anjHost:aiExample, type=DBR_SHORT, count=1, 
ctx="tux.aps.anl.gov:5064""
    Source File: ../getCopy.cpp line 86
    Current Time: Fri Jan 18 2008 09:15:33.826488069
..................................................................
ca_pend_io failed: User specified timeout on IO operation expired
ca_get failed: Virtual circuit disconnect
ca_pend_io failed: User specified timeout on IO operation expired
ca_get failed: Virtual circuit disconnect
ca_pend_io failed: User specified timeout on IO operation expired
ca_get failed: Virtual circuit disconnect
ca_pend_io failed: User specified timeout on IO operation expired
ca_pend_io returned 0x1: value=0x2
ca_pend_io returned 0x1: value=0x4
ca_pend_io returned 0x1: value=0x6

One other suggestion: In a CA client program like this, using 
ca_pend_event() instead of sleep() or epicsThreadSleep() can result in 
exception messages being printed sooner and the program seeming quicker 
to respond, since the CA library won't output anything while your code 
is not executing a CA library call.

- Andrew
--
When a distinguished but elderly scientist states that something is
possible, he is almost certainly right.  When he states that something
is impossible, he is very probably wrong.  -- Arthur C. Clarke

#include <stdlib.h>
#include <stdio.h>

#include <epicsThread.h>
#include <cadef.h>

#define EPICS_TIMEOUT 5.0


int main(int argc, char *argv[])
{
    char *PVN = "anjHost:aiExample";

    int rc;
    chid CID;
    double timeout = EPICS_TIMEOUT;
    unsigned short value;

    printf("calling ca_context_create\n");

    rc = ca_context_create(ca_disable_preemptive_callback);
    if (rc != ECA_NORMAL) {
        printf("ca_context_create failed %s\n", ca_message(rc));
        exit(1);
    }

    printf("calling ca_create_channel\n");

    rc = ca_create_channel(PVN, NULL, NULL, 10, &CID);
    if (rc != ECA_NORMAL) {
        printf("ca_create_channel failed: %s\n", ca_message(rc));
        exit(1);
    }

    printf("calling ca_pend_io(0)\n");

    rc = ca_pend_io(0);
    if (rc != ECA_NORMAL) {
        printf("ca_pend_io failed: %s\n", ca_message(rc));
        exit(1);
    }

    for(;;) {
        rc = ca_get(DBR_SHORT, CID, &value);
        if (rc != ECA_NORMAL) {
            printf("ca_get failed: %s\n", ca_message(rc));
        }

        rc = ca_pend_io(timeout);
        if (rc != ECA_NORMAL) {
            printf("ca_pend_io failed: %s\n", ca_message(rc));
        } else {
            printf("ca_pend_io returned 0x%x: value=0x%x\n", rc, value);
        }

        epicsThreadSleep(2);
    }

    exit(0);
}