RemoteStore: Add option to drop old connections from the pool

This is a hack to make hydra-queue-runner free its temproots
periodically, thereby ensuring that garbage collection of the
corresponding paths is not blocked until the queue runner is
restarted.

It would be better if temproots could be released earlier than at
process exit. I started working on a RAII object returned by functions
like addToStore() that releases temproots. However, this would be a
pretty massive change so I gave up on it for now.

1 files changed, 15 insertions, 1 deletions

diff --git a/src/libstore/remote-store.cc b/src/libstore/remote-store.cc
index 1af84cff5ba8..b9076c0474d6 100644
--- a/src/libstore/remote-store.cc
+++ b/src/libstore/remote-store.cc
@@ -45,7 +45,13 @@ RemoteStore::RemoteStore(const Params & params)
     , connections(make_ref<Pool<Connection>>(
             std::max(1, (int) maxConnections),
             [this]() { return openConnectionWrapper(); },
-            [](const ref<Connection> & r) { return r->to.good() && r->from.good(); }
+            [this](const ref<Connection> & r) {
+                return
+                    r->to.good()
+                    && r->from.good()
+                    && std::chrono::duration_cast<std::chrono::seconds>(
+                        std::chrono::steady_clock::now() - r->startTime).count() < maxConnectionAge;
+            }
             ))
 {
 }
@@ -106,6 +112,8 @@ ref<RemoteStore::Connection> UDSRemoteStore::openConnection()
     conn->from.fd = conn->fd.get();
     conn->to.fd = conn->fd.get();
 
+    conn->startTime = std::chrono::steady_clock::now();
+
     initConnection(*conn);
 
     return conn;
@@ -619,6 +627,12 @@ void RemoteStore::connect()
 }
 
 
+void RemoteStore::flushBadConnections()
+{
+    connections->flushBad();
+}
+
+
 RemoteStore::Connection::~Connection()
 {
     try {