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

src/libstore/build/entry-points.cc

@@ -15,7 +15,7 @@ void Store::buildPaths(const std::vector<DerivedPath> & reqs, BuildMode buildMod
         for (auto & br : reqs)
             goals.emplace_back(gf.makeGoal(br, buildMode));
         return goals;
-    });
+    }).wait(aio.waitScope).value();
 
     StringSet failed;
     std::shared_ptr<Error> ex;
@@ -54,7 +54,7 @@ std::vector<KeyedBuildResult> Store::buildPathsWithResults(
             goals.emplace_back(gf.makeGoal(req, buildMode));
         }
         return goals;
-    }).goals;
+    }).wait(aio.waitScope).value().goals;
 
     std::vector<KeyedBuildResult> results;
 
@@ -74,7 +74,7 @@ BuildResult Store::buildDerivation(const StorePath & drvPath, const BasicDerivat
             Worker::Targets goals;
             goals.emplace_back(gf.makeBasicDerivationGoal(drvPath, drv, OutputsSpec::All{}, buildMode));
             return goals;
-        });
+        }).wait(aio.waitScope).value();
         auto & result = results.goals.begin()->second;
         return result.result.restrictTo(DerivedPath::Built {
             .drvPath = makeConstantStorePathRef(drvPath),
@@ -100,7 +100,7 @@ void Store::ensurePath(const StorePath & path)
         Worker::Targets goals;
         goals.emplace_back(gf.makePathSubstitutionGoal(path));
         return goals;
-    });
+    }).wait(aio.waitScope).value();
     auto & result = results.goals.begin()->second;
 
     if (result.exitCode != Goal::ecSuccess) {
@@ -121,7 +121,7 @@ void Store::repairPath(const StorePath & path)
         Worker::Targets goals;
         goals.emplace_back(gf.makePathSubstitutionGoal(path, Repair));
         return goals;
-    });
+    }).wait(aio.waitScope).value();
     auto & result = results.goals.begin()->second;
 
     if (result.exitCode != Goal::ecSuccess) {
@@ -140,7 +140,7 @@ void Store::repairPath(const StorePath & path)
                     bmRepair
                 ));
                 return goals;
-            });
+            }).wait(aio.waitScope).value();
         } else
             throw Error(results.failingExitStatus, "cannot repair path '%s'", printStorePath(path));
     }

src/libstore/build/worker.cc

@@ -229,8 +229,8 @@ try {
     co_return result::failure(std::current_exception());
 }
 
-Worker::Results Worker::run(std::function<Targets (GoalFactory &)> req)
-{
+kj::Promise<Result<Worker::Results>> Worker::run(std::function<Targets (GoalFactory &)> req)
+try {
     auto topGoals = req(goalFactory());
 
     assert(!running);
@@ -252,7 +252,9 @@ Worker::Results Worker::run(std::function<Targets (GoalFactory &)> req)
         promise = promise.exclusiveJoin(boopGC(*localStore));
     }
 
-    return promise.wait(aio.waitScope).value();
+    co_return co_await promise;
+} catch (...) {
+    co_return result::failure(std::current_exception());
 }
 
 kj::Promise<Result<Worker::Results>> Worker::runImpl(Targets topGoals)

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());
 }
 }