libstore: make waiting for a while a promise

this simplifies waitForInput quite a lot, and at the same time makes
polling less thundering-herd-y. it even fixes early polling wakeups!

Change-Id: I6dfa62ce91729b8880342117d71af5ae33366414

1 files changed, 13 insertions, 0 deletions

diff --git a/src/libstore/build/goal.cc b/src/libstore/build/goal.cc
index 82861ad2b..649093dbd 100644
--- a/src/libstore/build/goal.cc
+++ b/src/libstore/build/goal.cc
@@ -1,4 +1,6 @@
 #include "goal.hh"
+#include "worker.hh"
+#include <kj/time.h>
 
 namespace nix {
 
@@ -15,4 +17,15 @@ void Goal::trace(std::string_view s)
     debug("%1%: %2%", name, s);
 }
 
+kj::Promise<Result<Goal::WorkResult>> Goal::waitForAWhile()
+try {
+    trace("wait for a while");
+    /* If we are polling goals that are waiting for a lock, then wake
+       up after a few seconds at most. */
+    co_await worker.aio.provider->getTimer().afterDelay(settings.pollInterval.get() * kj::SECONDS);
+    co_return ContinueImmediately{};
+} catch (...) {
+    co_return std::current_exception();
+}
+
 }