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refactor(client): add comments about the checkout vs connect race

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This commit is contained in:
Sean McArthur
2018-09-28 12:50:45 -07:00
parent 09156a70a6
commit efd2c281b8
1 changed files with 16 additions and 3 deletions
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19
src/client/mod.rs
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@@ -281,11 +281,11 @@ where C: Connect + Sync + 'static,
} }
fn send_request(&self, mut req: Request<B>, pool_key: PoolKey) -> impl Future<Item=Response<Body>, Error=ClientError<B>> { fn send_request(&self, mut req: Request<B>, pool_key: PoolKey) -> impl Future<Item=Response<Body>, Error=ClientError<B>> {
let race = self.pool_checkout_or_connect(req.uri().clone(), pool_key); let conn = self.connection_for(req.uri().clone(), pool_key);
let ver = self.ver; let ver = self.ver;
let executor = self.executor.clone(); let executor = self.executor.clone();
race.and_then(move |mut pooled| { conn.and_then(move |mut pooled| {
if ver == Ver::Http1 { if ver == Ver::Http1 {
// CONNECT always sends origin-form, so check it first... // CONNECT always sends origin-form, so check it first...
if req.method() == &Method::CONNECT { if req.method() == &Method::CONNECT {
@@ -365,9 +365,22 @@ where C: Connect + Sync + 'static,
}) })
} }
fn pool_checkout_or_connect(&self, uri: Uri, pool_key: PoolKey) fn connection_for(&self, uri: Uri, pool_key: PoolKey)
-> impl Future<Item=Pooled<PoolClient<B>>, Error=ClientError<B>> -> impl Future<Item=Pooled<PoolClient<B>>, Error=ClientError<B>>
{ {
// This actually races 2 different futures to try to get a ready
// connection the fastest, and to reduce connection churn.
//
// - If the pool has an idle connection waiting, that's used
// immediately.
// - Otherwise, the Connector is asked to start connecting to
// the destination Uri.
// - Meanwhile, the pool Checkout is watching to see if any other
// request finishes and tries to insert an idle connection.
// - If a new connection is started, but the Checkout wins after
// (an idle connection becamse available first), the started
// connection future is spawned into the runtime to complete,
// and then be inserted into the pool as an idle connection.
let checkout = self.pool.checkout(pool_key.clone()); let checkout = self.pool.checkout(pool_key.clone());
let connect = self.connect_to(uri, pool_key); let connect = self.connect_to(uri, pool_key);