# HG changeset patch # User Aleksei Bavshin # Date 1654139843 25200 # Node ID aa28c802409fb7a74e3323195f859d09fe73cd6d # Parent 457afc332c670ad04546c72ff6e8badc692f3233 Resolver: make TCP write timer event cancelable. Similar to 70e65bf8dfd7, the change is made to ensure that the ability to cancel resolver tasks is fully controlled by the caller. As mentioned in the referenced commit, it is safe to make this timer cancelable because resolve tasks can have their own timeouts that are not cancelable. The scenario where this may become a problem is a periodic background resolve task (not tied to a specific request or a client connection), which receives a response with short TTL, large enough to warrant fallback to a TCP query. With each event loop wakeup, we either have a previously set write timer instance or schedule a new one. The non-cancelable write timer can delay or block graceful shutdown of a worker even if the ngx_resolver_ctx_t->cancelable flag is set by the API user, and there are no other tasks or connections. We use the resolver API in this way to maintain the list of upstream server addresses specified with the 'resolve' parameter, and there could be third-party modules implementing similar logic. diff --git a/src/core/ngx_resolver.c b/src/core/ngx_resolver.c --- a/src/core/ngx_resolver.c +++ b/src/core/ngx_resolver.c @@ -1389,6 +1389,7 @@ ngx_resolver_send_tcp_query(ngx_resolver rec->tcp->data = rec; rec->tcp->write->handler = ngx_resolver_tcp_write; + rec->tcp->write->cancelable = 1; rec->tcp->read->handler = ngx_resolver_tcp_read; rec->tcp->read->resolver = 1;