达梦数据库-C外部函数创建，及与Plsql自定义函数效率对比

一、测试环境信息

名称	描述
*** 作系统	CentOS Linux release 7.9.2009 (Core)
达梦数据版本	V8 1-2-38-21.07.09-143359-10018-ENT

二、测试步骤
（1）修改参数，重启数据库

sp_set_para_value(2,'ENABLE_EXTERNAL_CALL',1);

（2）查看是否修改成功，为1表示成功

select PARA_NAME,PARA_VALUE from v$dm_ini where PARA_NAME='ENABLE_EXTERNAL_CALL';

（3）C外部函数源码–实现0到某数的累加
vim multithreading_v2.c添加如下内容：

#include 
#include 
#include 

typedef struct Test_Struct
{
    int id;
    long num1;
    long num2;
    long result;
    struct Test_Struct *next;
} TS;

void *ComputeSum(void *args);
TS* CreateHeadList();
void InsertListData(TS* head, int p_id, long p_num1, long p_num2, long p_result);
TS* GetListDataP(TS* head, int p_id);
char* PrintfList(TS* head);
char* MULTITHREADING(int pthread_num, long num);
/*
void main()
{
    long num = 100000000;
    int pthread_num = 3;
    MULTITHREADING(pthread_num, num);
}
*/
char* MULTITHREADING(int pthread_num, long num)
{
    int i;
    long temp = 0;
    TS *ts = CreateHeadList();
    pthread_t *th_arr = (pthread_t *)malloc(sizeof(pthread_t) * pthread_num);
    for(i=0; i<pthread_num; i++)
    {
        if(i == pthread_num - 1)
        {
            InsertListData(ts, i, temp, num - ts->num1, 0);
        }
        else
        {
            InsertListData(ts, i, temp, temp + (num / pthread_num), 0);
            temp = temp + (num / pthread_num) + 1;
        }
        pthread_create(&(th_arr[i]),NULL,ComputeSum,GetListDataP(ts,i));
    }
    for(i=0; i<pthread_num; i++)
    {
        pthread_join(th_arr[i],NULL);
    }
    return PrintfList(ts);
}

void *ComputeSum(void *args)
{
    TS* ts = (TS*)malloc(sizeof(TS));
    ts = args;
    long i;
    for(i = ts->num1; i <= ts->num2; i++)
    {
        ts->result = ts->result + i;
    }
    //printf("pthread_id(%d), num1 : %4ld, num2: %4ld, result : %ld\n",ts->id,ts->num1,ts->num2,ts->result);
    return NULL;
}

TS* CreateHeadList() 
{
    TS* head = (TS*)malloc(sizeof(TS));
    head->id = -1;
    head->num1 = 0;
    head->num2 = 0;
    head->result = 0;
    head->next = NULL;
    return head;
};

void InsertListData(TS* head, int p_id, long p_num1, long p_num2, long p_result) 
{
    TS* p = head;
    while (p->next != NULL)
    {
        p = p->next;
    }
    TS* q = (TS*)malloc(sizeof(TS));
    q->id = p_id;
    q->num1 = p_num1;
    q->num2 = p_num2;
    q->result = p_result;
    q->next = NULL;
    p->next = q;
}

TS* GetListDataP(TS* head, int p_id)
{
    TS* p = head;
    while(p !=NULL)
    {
        if(p->id == p_id)
        {
            return p;
        }
        p = p->next;
    }
    return NULL;
}

char* PrintfList(TS* head) {
    long res = 0;
    char *str_res = malloc(sizeof(char)*17);
    TS* ts = head;
    while (ts != NULL) 
    {
        res = res + ts->result;
        //printf("id : %3d, num1 : %4ld, num2: %4ld, result : %ld, next : %o\n",ts->id,ts->num1,ts->num2,ts->result,ts->next);
        ts = ts->next;
    }
    //printf("res : %ld\n",res);
    //printf("+++++++++++++++++++++\n");
    sprintf(str_res, "%lld", res);
    return str_res;
}

（4）编译

gcc -o /opt/libtest.so -fPIC -shared multithreading_v2.c

（5）建C外部函数（此函数仅支持X86平台）

CREATE OR REPLACE FUNCTION multipthread_sum(pthread_num int,num integer)  
RETURN varchar EXTERNAL '/opt/libtest.so' MULTITHREADING USING CS;

函数介绍：
pthread_num ：表示线程数。

num ：需要累加到的值，0加到num。

（6）建Plsql自定义函数–实现同样的功能

create or replace function psql_sum(num integer)
RETURN bigint
as
declare
	i integer;
	sum bigint:= 0;
begin
	for i in 1..num loop
		sum := sum + i;
	end loop;
	return sum;
end;
/

（7）效率对比