libstore: turn Worker in a kj event loop user

using a proper event loop basis we no longer have to worry about most of
the intricacies of poll(), or platform-dependent replacements for it. we
may even be able to use the event loop and its promise system for all of
our scheduling in the future. we don't do any real async processing yet,
this is just preparation to separate the first such change from the huge
api design difference with the async framework we chose (kj from capnp):

kj::Promise, unlike std::future, doesn't return exceptions unmangled. it
instead wraps any non-kj exception into a kj exception, erasing all type
information and preserving mostly the what() string in the process. this
makes sense in the capnp rpc use case where unrestricted exception types
can't be transferred, and since it moves error handling styles closer to
a world we'd actually like there's no harm in doing it only here for now

Change-Id: I20f888de74d525fb2db36ca30ebba4bcfe9cc838

1 files changed, 7 insertions, 7 deletions

diff --git a/src/libstore/build/substitution-goal.hh b/src/libstore/build/substitution-goal.hh
index 9c7e6f470..3c97b19fd 100644
--- a/src/libstore/build/substitution-goal.hh
+++ b/src/libstore/build/substitution-goal.hh
@@ -67,7 +67,7 @@ struct PathSubstitutionGoal : public Goal
     NotifyingCounter<uint64_t>::Bump maintainExpectedSubstitutions,
         maintainRunningSubstitutions, maintainExpectedNar, maintainExpectedDownload;
 
-    typedef WorkResult (PathSubstitutionGoal::*GoalState)(bool inBuildSlot);
+    typedef kj::Promise<Result<WorkResult>> (PathSubstitutionGoal::*GoalState)(bool inBuildSlot) noexcept;
     GoalState state;
 
     /**
@@ -101,16 +101,16 @@ public:
         return "a$" + std::string(storePath.name()) + "$" + worker.store.printStorePath(storePath);
     }
 
-    WorkResult work(bool inBuildSlot) override;
+    kj::Promise<Result<WorkResult>> work(bool inBuildSlot) noexcept override;
 
     /**
      * The states.
      */
-    WorkResult init(bool inBuildSlot);
-    WorkResult tryNext(bool inBuildSlot);
-    WorkResult referencesValid(bool inBuildSlot);
-    WorkResult tryToRun(bool inBuildSlot);
-    WorkResult finished(bool inBuildSlot);
+    kj::Promise<Result<WorkResult>> init(bool inBuildSlot) noexcept;
+    kj::Promise<Result<WorkResult>> tryNext(bool inBuildSlot) noexcept;
+    kj::Promise<Result<WorkResult>> referencesValid(bool inBuildSlot) noexcept;
+    kj::Promise<Result<WorkResult>> tryToRun(bool inBuildSlot) noexcept;
+    kj::Promise<Result<WorkResult>> finished(bool inBuildSlot) noexcept;
 
     /**
      * Callback used by the worker to write to the log.