Experimental Physics and
Industrial Control System

<[email protected]> · Tue, 23 Apr 2013 08:18:20 +0000

I've finally isolated the issue when calling ca_context_create(1) late ... and it's something to do with how the zero count is handled in ca_array_get_callback -- to be precise, when calling

	ca_array_get_callback(dbrcode, 0, channel, callback, context)

the size of the returned array differs, depending on whether ca_context_create(1) was called before or after iocInit!  Note that this problem only occurs with internal PVs, for external PVs the correct count is returned in both cases.

I've attached a complete example IOC -- just compile it and run `test` or `test 1` in the root.  Running `test` will call ca_context_create(1) late and will print out 'count = 0'; running `test 1` calls ca_context_create(1) early and prints out 'count = 1'.  I've tested this with both 3.14.11 and 3.14.12.3.

I can't find documentation for the expected behaviour of calling ca_array_get_callback() with a zero count, but I've never encountered problems with this before: up to now I've expected to get the "natural" record size.  Note that if the PV being fetched is an external PV then 'count = 1' is printed as expected.

Note, by the way, that my earlier diagnosis (that something else was also calling ca_context_create() and conflicting) appears to have been completely wrong.  Sorry about the red herring.

Here's the core of the IOC:

test.c
======
#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

#include <cadef.h>
#include <iocsh.h>

static chid pv_channel;

static void on_get(struct event_handler_args args)
{
    printf("on get\n");
    printf("count = %ld\n", args.count);
}

static void on_ca_connect(struct connection_handler_args args)
{
    printf("on connect\n");
    ca_array_get_callback(3, 0, pv_channel, on_get, NULL);
}

int main(int argc, char **argv)
{
    bool early_create = argc > 1  &&  *argv[1] == '1';
    printf("Creating CA context %s\n", early_create ? "early" : "late");

    if (early_create)
        ca_context_create(1);
    iocsh("TEST.cmd");
    if (!early_create)
        ca_context_create(1);

    ca_create_channel("TESTPV", on_ca_connect, NULL, 0, &pv_channel);

    sleep(1);
    return 0;
}

TEST.cmd
========
dbLoadDatabase("dbd/TEST.dbd", NULL, NULL)
TEST_registerRecordDeviceDriver(pdbbase)
dbLoadRecords("TEST.db", NULL)
iocInit()

TEST.db
=======
record(bo, "TESTPV")
{
}

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System