update global values in high-concurrency situation

weicong19q3 · 2018-08-24T14:52:14+00:00

On Wednesday, August 22, 2018 at 4:08:49 PM UTC+3, Kwanhur Huang wrote:hello,in context of log_by_lua*, it just send msg content into buffer, and then do_flu...

update global values in high-concurrency situation

weicong19q3

Hey folks,

I am doing things that counting the times of upstream be selected.

I store this counting number in a table, and put table to a global value G. And i initial it in init phase. The structure of the globle value G likes below

G = {
 ['upstream_1'] = {
 ['host'] = '1.0.0.1',
 ['count'] = 100
 },


 ['upstream_2'] = {
 ['host'] = '2.0.0.2',
 ['count'] = 200
 }
}

I will increase the count of selected upstream by 1 in body_filter_by_lua_file phase. Meanwhile, I will create a ngx.timer after increasing and the timer will decrease the count by 1 after delay

increase_count(selected_upstream)
ngx.timer.at(delay, decrease_count_function, selectd_upstream)

while, the request is small, everything seems ok. But when request is large, there will be a number of ngx.timer created which will cause competition of global value count and the result of couting will be wrong.

I consider to use lua_shared_dict, but it does not support to put table in it. And also i consider to serialize the table by json and put it to shared_dict which is clumsy.

So, how you process this problem that updating global values in high-concurrency situation

zchao1995

Hello!

I don't know what is your demand,

it feels strange that decreases the count inside a timer handler.

Anyway, from my perspective, you may just need a sole timer,

you can create it by the ngx.timer.every. What's more, the count decreasing

may be organized to a FIFO queue, combined with a delay, maybe.

In addition, the usage of global variables is not recommended, using module level variables

is a better idea.