access_by_lua does not seem consistent

[gnois]

For the below nginx.conf, path /a, /c and /e gives expected output 403 forbidden.

But for path /b and /d, the first invocation gives 500 internal server error. Invoking the same path again in future gives 404 not found.

nginx.conf

worker_processes 1;
error_log logs/error.log notice;
daemon off;
events {
    worker_connections 1024;
}

http {
    server {
        listen 8888;

        location /a {
           access_by_lua_block {
               return ngx.exit(ngx.HTTP_FORBIDDEN)
           }
        }

        # 500, then 404
        location /b {
           access_by_lua_block {
               require('access')
           }
        }

        location /c {
           access_by_lua "return ngx.exit(ngx.HTTP_FORBIDDEN)";
        }

        # 500, then 404
        location /d {
           access_by_lua "require('access')";
        }

        location /e {
           access_by_lua_file "access.lua";
        }

    }
}

access.lua

return ngx.exit(ngx.HTTP_FORBIDDEN)

Here is the partial error.log after invoking path /b

[error] 9657#100092: *1 lua entry thread aborted: runtime error: attempt to yield across C-call boundary
stack traceback:
coroutine 0:
        [C]: in function 'require'
        access_by_lua(nginx.conf:22):2: in main chunk, client: 192.168.50.96, server: , request: "GET /b HTTP/1.1", host: "192.168.50.124:8888"
[error] 9657#100092: *2 open() "./html/b" failed (2: No such file or directory), client: 192.168.50.96, server: , request: "GET /b HTTP/1.1", host: "192.168.50.124:8888"

OpenResty 1.19.3.1 on Windows and FreeBSD

[LubinLew]

see openresty/lua-resty-redis#3 ,this is a limit of require function