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[block-sync] Don't hold client-cache lock while connecting

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`lightning-block-sync`'s REST and RPC clients both hold a cache for
a connected client to avoid the extra connection round-trip on each
request. Because only one client can be using a connection at once,
the connection is `take()`n out of an `Option` behind a `Mutex` and
if there isn't one present, we call `HttpClient::connect` to build
a new one.

However, this full logic is completed in one statement, causing a
client-cache lock to be held during `HttpClient::connect`. This
can turn into quite a bit of contention when using these clients as
gossip verifiers as we can create many requests back-to-back during
startup.

I noticed this as my node during startup only seemed to be
saturating one core and managed to get a backtrace that showed
several threads being blocked on this mutex when hitting a Bitcoin
Core node over REST that is on the same LAN, but not the same
machine.
This commit is contained in:
Matt Corallo 2024-07-21 23:29:19 +00:00
parent 9ce3dd5269
commit 7945af700d
2 changed files with 4 additions and 2 deletions
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3
lightning-block-sync/src/rest.rs
View file

@ -34,7 +34,8 @@ impl RestClient {
{
let host = format!("{}:{}", self.endpoint.host(), self.endpoint.port());
let uri = format!("{}/{}", self.endpoint.path().trim_end_matches("/"), resource_path);
let mut client = if let Some(client) = self.client.lock().unwrap().take() {
let reserved_client = self.client.lock().unwrap().take();
let mut client = if let Some(client) = reserved_client {
client
} else {
HttpClient::connect(&self.endpoint)?

3
lightning-block-sync/src/rpc.rs
View file

@ -77,7 +77,8 @@ impl RpcClient {
"id": &self.id.fetch_add(1, Ordering::AcqRel).to_string()
});
let mut client = if let Some(client) = self.client.lock().unwrap().take() {
let reserved_client = self.client.lock().unwrap().take();
let mut client = if let Some(client) = reserved_client {
client
} else {
HttpClient::connect(&self.endpoint)?