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, 14 insertions, 14 deletions

diff --git a/src/libstore/build/derivation-goal.hh b/src/libstore/build/derivation-goal.hh
index bf4a3da93..020388d5a 100644
--- a/src/libstore/build/derivation-goal.hh
+++ b/src/libstore/build/derivation-goal.hh
@@ -213,7 +213,7 @@ struct DerivationGoal : public Goal
      */
     std::optional<DerivationType> derivationType;
 
-    typedef WorkResult (DerivationGoal::*GoalState)(bool inBuildSlot);
+    typedef kj::Promise<Result<WorkResult>> (DerivationGoal::*GoalState)(bool inBuildSlot) noexcept;
     GoalState state;
 
     BuildMode buildMode;
@@ -246,7 +246,7 @@ struct DerivationGoal : public Goal
 
     std::string key() override;
 
-    WorkResult work(bool inBuildSlot) override;
+    kj::Promise<Result<WorkResult>> work(bool inBuildSlot) noexcept override;
 
     /**
      * Add wanted outputs to an already existing derivation goal.
@@ -256,18 +256,18 @@ struct DerivationGoal : public Goal
     /**
      * The states.
      */
-    WorkResult getDerivation(bool inBuildSlot);
-    WorkResult loadDerivation(bool inBuildSlot);
-    WorkResult haveDerivation(bool inBuildSlot);
-    WorkResult outputsSubstitutionTried(bool inBuildSlot);
-    WorkResult gaveUpOnSubstitution(bool inBuildSlot);
-    WorkResult closureRepaired(bool inBuildSlot);
-    WorkResult inputsRealised(bool inBuildSlot);
-    WorkResult tryToBuild(bool inBuildSlot);
-    virtual WorkResult tryLocalBuild(bool inBuildSlot);
-    WorkResult buildDone(bool inBuildSlot);
+    kj::Promise<Result<WorkResult>> getDerivation(bool inBuildSlot) noexcept;
+    kj::Promise<Result<WorkResult>> loadDerivation(bool inBuildSlot) noexcept;
+    kj::Promise<Result<WorkResult>> haveDerivation(bool inBuildSlot) noexcept;
+    kj::Promise<Result<WorkResult>> outputsSubstitutionTried(bool inBuildSlot) noexcept;
+    kj::Promise<Result<WorkResult>> gaveUpOnSubstitution(bool inBuildSlot) noexcept;
+    kj::Promise<Result<WorkResult>> closureRepaired(bool inBuildSlot) noexcept;
+    kj::Promise<Result<WorkResult>> inputsRealised(bool inBuildSlot) noexcept;
+    kj::Promise<Result<WorkResult>> tryToBuild(bool inBuildSlot) noexcept;
+    virtual kj::Promise<Result<WorkResult>> tryLocalBuild(bool inBuildSlot) noexcept;
+    kj::Promise<Result<WorkResult>> buildDone(bool inBuildSlot) noexcept;
 
-    WorkResult resolvedFinished(bool inBuildSlot);
+    kj::Promise<Result<WorkResult>> resolvedFinished(bool inBuildSlot) noexcept;
 
     /**
      * Is the build hook willing to perform the build?
@@ -346,7 +346,7 @@ struct DerivationGoal : public Goal
      */
     virtual void killChild();
 
-    WorkResult repairClosure();
+    kj::Promise<Result<WorkResult>> repairClosure() noexcept;
 
     void started();