Lost connection to MySQL server during aggregate UDF execution

Question

I created a MySQL UDF in C++ and uploaded it into the MySQL's plugin directory. I am able to install the UDF in MySQL, but when I try to call it, the MySQL server stops. I am using visual studio 2019 to create the shared library(.dll in windows) on windows 10 operating system.

I am calling a method from java in my MySQL C++ UDF, I am using graalVM to call the java methods from C++ functions.

I created a shared library out of my java code and I use them in my C++ code to access my java methods.

MySQL UDF code:DemoAgg.cpp

#ifdef STANDARD

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#ifdef __WIN__
typedef unsigned __int64 ulonglong;
typedef __int64 longlong;
#else
typedef unsigned long long ulonglong;
typedef long long longlong;
#endif /*__WIN__*/
#endif
#include <mysql.h>
#include <iostream>
#include <ctype.h>
#include <demolibmysqlagg.h>

extern "C" bool test_agg_init(UDF_INIT * initid, UDF_ARGS * args, char* message)
{
    long long* i = new long long; 
    *i = 0;                    
    initid->ptr = (char*)i;

    std::cout << "in init func" << std::endl;

    if (args->arg_count != 1)
    {
        strcpy_s(message, 50, "testagg() requires one arguments");
        return 1;
    }

    if (args->arg_type[0] != INT_RESULT)
    {
        strcpy_s(message, 50, "testagg() requires one integer");
        return 1;
    }
    return 0;
}

extern "C" void test_agg_deinit(UDF_INIT * initid)
{
    std::cout << "in deinit func" << std::endl;
    delete (long long*)initid->ptr;
}

extern "C" void test_agg_clear(UDF_INIT* initid, char* is_null, char* error)
{
    std::cout << "in clear func" << std::endl;
    *((long long*)initid->ptr) = 0;
}

extern "C" void test_agg_add(UDF_INIT* initid, UDF_ARGS* args, char* is_null, char* error)
{
    graal_isolate_t* isolate = NULL;
    graal_isolatethread_t* thread = NULL;

    std::cout << "in add func" << std::endl;

    long long int_val;
    int_val = *((long long*)initid->ptr);

    long long int_val2;
    int_val2 = *((long long*)args->args[0]);

    long long sum;
    sum = aggadd(thread, int_val, int_val2);     //my java method which i call from this program
    std::cout << sum;

    *((long long*)initid->ptr) = sum;
}

extern "C" long long test_agg(UDF_INIT* initid, UDF_ARGS* args, char* is_null, char* error)
{
    std::cout <<"in main func"<<std::endl;
    return *((long long*)initid->ptr);
}

My Module Definition File:DemoAgg.def

LIBRARY testagg

EXPORTS
         test_agg_init
         test_agg_deinit
         test_agg_clear
         test_agg_add
         test_agg

My java code:

package testmysql;

import org.graalvm.nativeimage.IsolateThread;
import org.graalvm.nativeimage.c.function.CEntryPoint;

public class demo_mysqlagg {

    @CEntryPoint (name = "aggadd")
    public static int aggadd(IsolateThread thread, int x, int y) {
            return x+y;
    }
}

After building my C++ project, I get a dll file which I copy to the MySQL's plugin directory.

I install the UDF using the following query:

create aggregate function test_agg returns integer soname 'testagg.dll';

I call my UDF using the following query:

select test_agg(c1) from demo_agg;

where,

demo_agg is a table with only one column.

c1 is the column name of type integer.

But when I execute the above query, the following error pops up:

18:52:53    select test_agg(c1) from demo_agg LIMIT 0, 1000 Error Code: 2013. Lost connection to MySQL server during query  0.063 sec

My error log:

2020-09-29T14:41:24.584058Z 0 [Warning] [MY-010915] [Server] 'NO_ZERO_DATE', 'NO_ZERO_IN_DATE' and 'ERROR_FOR_DIVISION_BY_ZERO' sql modes should be used with strict mode. They will be merged with strict mode in a future release.
2020-09-29T14:41:24.587014Z 0 [System] [MY-010116] [Server] C:\Program Files\MySQL\MySQL Server 8.0\bin\mysqld.exe (mysqld 8.0.21) starting as process 48276
2020-09-29T14:41:24.653757Z 1 [System] [MY-013576] [InnoDB] InnoDB initialization has started.
2020-09-29T14:41:28.123852Z 1 [System] [MY-013577] [InnoDB] InnoDB initialization has ended.
2020-09-29T14:41:28.958692Z 0 [System] [MY-011323] [Server] X Plugin ready for connections. Bind-address: '::' port: 33060
2020-09-29T14:41:30.249252Z 0 [Warning] [MY-010068] [Server] CA certificate ca.pem is self signed.
2020-09-29T14:41:30.250713Z 0 [System] [MY-013602] [Server] Channel mysql_main configured to support TLS. Encrypted connections are now supported for this channel.
2020-09-29T14:41:30.653518Z 0 [System] [MY-010931] [Server] C:\Program Files\MySQL\MySQL Server 8.0\bin\mysqld.exe: ready for connections. Version: '8.0.21'  socket: ''  port: 3306  MySQL Community Server - GPL.
in init func
in clear func
in add func
2020-09-29T14:42:49.045501Z 0 [Warning] [MY-010915] [Server] 'NO_ZERO_DATE', 'NO_ZERO_IN_DATE' and 'ERROR_FOR_DIVISION_BY_ZERO' sql modes should be used with strict mode. They will be merged with strict mode in a future release.
2020-09-29T14:42:49.053090Z 0 [System] [MY-010116] [Server] C:\Program Files\MySQL\MySQL Server 8.0\bin\mysqld.exe (mysqld 8.0.21) starting as process 188880
2020-09-29T14:42:49.102031Z 1 [System] [MY-013576] [InnoDB] InnoDB initialization has started.
2020-09-29T14:42:53.150956Z 1 [System] [MY-013577] [InnoDB] InnoDB initialization has ended.
2020-09-29T14:42:53.914379Z 0 [System] [MY-011323] [Server] X Plugin ready for connections. Bind-address: '::' port: 33060
2020-09-29T14:42:54.728381Z 0 [System] [MY-010229] [Server] Starting XA crash recovery...
2020-09-29T14:42:54.737801Z 0 [System] [MY-010232] [Server] XA crash recovery finished.
2020-09-29T14:42:55.464369Z 0 [Warning] [MY-010068] [Server] CA certificate ca.pem is self signed.
2020-09-29T14:42:55.465965Z 0 [System] [MY-013602] [Server] Channel mysql_main configured to support TLS. Encrypted connections are now supported for this channel.
2020-09-29T14:42:56.133327Z 0 [System] [MY-010931] [Server] C:\Program Files\MySQL\MySQL Server 8.0\bin\mysqld.exe: ready for connections. Version: '8.0.21'  socket: ''  port: 3306  MySQL Community Server - GPL.

I put some cout statements to know in which function I am.

Can anyone help me out here? What I am doing here? Any kind of help or suggestion will be of great help.

Answer 1

the problem is with:

graal_isolate_t* isolate = NULL;
graal_isolatethread_t* thread = NULL;

they are null, that's why it is not able to call the java method and the connection is getting timed out.

if I initialize them like this:

if (graal_create_isolate(NULL, &isolate, &thread) != 0) {
        fprintf(stderr, "initialization error\n");
        return;
    }

then it is working fine.