libstore: turn Worker::run into a promise

a first little step into pushing the event loops up, up and away.
eventually we will want them to be instantiated only at the roots
of every thread (since kj binds loops to threads), but not today.

Change-Id: Ic97f1debba382a5a3f46daeaf2d6d434ee42569f

1 files changed, 11 insertions, 7 deletions

diff --git a/src/libstore/build/worker.hh b/src/libstore/build/worker.hh
index dc5e0e878..369e58b41 100644
--- a/src/libstore/build/worker.hh
+++ b/src/libstore/build/worker.hh
@@ -278,7 +278,7 @@ public:
     /**
      * Loop until the specified top-level goals have finished.
      */
-    Results run(std::function<Targets (GoalFactory &)> req);
+    kj::Promise<Result<Results>> run(std::function<Targets (GoalFactory &)> req);
 
     /**
      * Check whether the given valid path exists and has the right
@@ -289,14 +289,18 @@ public:
     void markContentsGood(const StorePath & path);
 
     template<typename MkGoals>
-    friend Results
-    processGoals(Store & store, Store & evalStore, kj::AsyncIoContext & aio, MkGoals && mkGoals);
+    friend kj::Promise<Result<Results>> processGoals(
+        Store & store, Store & evalStore, kj::AsyncIoContext & aio, MkGoals && mkGoals
+    ) noexcept;
 };
 
 template<typename MkGoals>
-Worker::Results
-processGoals(Store & store, Store & evalStore, kj::AsyncIoContext & aio, MkGoals && mkGoals)
-{
-    return Worker(store, evalStore, aio).run(std::forward<MkGoals>(mkGoals));
+kj::Promise<Result<Worker::Results>> processGoals(
+    Store & store, Store & evalStore, kj::AsyncIoContext & aio, MkGoals && mkGoals
+) noexcept
+try {
+    co_return co_await Worker(store, evalStore, aio).run(std::forward<MkGoals>(mkGoals));
+} catch (...) {
+    co_return result::failure(std::current_exception());
 }
 }