libstore: propagate goal exceptions using promises

drop childException since it's no longer needed. also makes
waitForInput, childFinished, and childTerminated redundant.

Change-Id: I05d88ffd323c5b5c909ac21056162f69ffb0eb9f

src/libstore/build/goal.cc

@@ -57,6 +57,7 @@ try {
 
     while (auto item = co_await collectDeps.next()) {
         auto & [dep, _result] = *item;
+        BOOST_OUTCOME_CO_TRYV(_result);
 
         waiteeDone(dep);
 

src/libstore/build/worker.cc

@@ -1,3 +1,4 @@
+#include "async-collect.hh"
 #include "charptr-cast.hh"
 #include "worker.hh"
 #include "finally.hh"
@@ -6,6 +7,8 @@
 #include "local-derivation-goal.hh"
 #include "signals.hh"
 #include "hook-instance.hh" // IWYU pragma: keep
+#include <boost/outcome/try.hpp>
+#include <kj/vector.h>
 
 namespace nix {
 
@@ -231,20 +234,9 @@ void Worker::childStarted(GoalPtr goal, kj::Promise<Result<Goal::WorkResult>> pr
             if (result.has_value()) {
                 goalFinished(goal, result.assume_value());
             } else {
-                childException = result.assume_error();
-            }
-        })
-        .attach(Finally{[this, goal] {
-            childTerminated(goal);
-        }}));
-}
-
-
-void Worker::childTerminated(GoalPtr goal)
-{
-    if (childFinished) {
-        childFinished->fulfill();
+                goal->notify->fulfill(result.assume_error());
             }
+        }));
 }
 
 
@@ -282,9 +274,12 @@ std::vector<GoalPtr> Worker::run(std::function<Targets (GoalFactory &)> req)
     running = true;
     Finally const _stop([&] { running = false; });
 
+    std::vector<GoalPtr> results;
+
     topGoals.clear();
     for (auto & [goal, _promise] : _topGoals) {
         topGoals.insert(goal);
+        results.push_back(goal);
     }
 
     auto onInterrupt = kj::newPromiseAndCrossThreadFulfiller<Result<void>>();
@@ -292,8 +287,9 @@ std::vector<GoalPtr> Worker::run(std::function<Targets (GoalFactory &)> req)
         return result::failure(std::make_exception_ptr(makeInterrupted()));
     });
 
-    auto promise =
-        runImpl().exclusiveJoin(updateStatistics()).exclusiveJoin(std::move(onInterrupt.promise));
+    auto promise = runImpl(std::move(_topGoals))
+                       .exclusiveJoin(updateStatistics())
+                       .exclusiveJoin(std::move(onInterrupt.promise));
 
     // TODO GC interface?
     if (auto localStore = dynamic_cast<LocalStore *>(&store); localStore && settings.minFree != 0) {
@@ -303,27 +299,24 @@ std::vector<GoalPtr> Worker::run(std::function<Targets (GoalFactory &)> req)
 
     promise.wait(aio.waitScope).value();
 
-    std::vector<GoalPtr> results;
-    for (auto & [i, _p] : _topGoals) {
-        results.push_back(i);
-    }
     return results;
 }
 
-kj::Promise<Result<void>> Worker::runImpl()
+kj::Promise<Result<void>> Worker::runImpl(Targets _topGoals)
 try {
     debug("entered goal loop");
 
-    while (1) {
-        if (topGoals.empty()) break;
-
-        /* Wait for input. */
-        if (!children.isEmpty())
-            (co_await waitForInput()).value();
-
-        if (childException) {
-            std::rethrow_exception(childException);
+    kj::Vector<Targets::value_type> promises(_topGoals.size());
+    for (auto & gp : _topGoals) {
+        promises.add(std::move(gp));
     }
+
+    auto collect = AsyncCollect(promises.releaseAsArray());
+    while (auto done = co_await collect.next()) {
+        // propagate goal exceptions outward
+        BOOST_OUTCOME_CO_TRYV(done->second);
+
+        if (topGoals.empty()) break;
     }
 
     /* If --keep-going is not set, it's possible that the main goal
@@ -346,18 +339,6 @@ try {
     co_return result::failure(std::current_exception());
 }
 
-kj::Promise<Result<void>> Worker::waitForInput()
-try {
-    printMsg(lvlVomit, "waiting for children");
-
-    auto pair = kj::newPromiseAndFulfiller<void>();
-    this->childFinished = kj::mv(pair.fulfiller);
-    co_await pair.promise;
-    co_return result::success();
-} catch (...) {
-    co_return result::failure(std::current_exception());
-}
-
 
 unsigned int Worker::failingExitStatus()
 {

src/libstore/build/worker.hh

@@ -84,6 +84,9 @@ protected:
  */
 class Worker : public WorkerBase
 {
+public:
+    using Targets = std::map<GoalPtr, kj::Promise<Result<Goal::WorkResult>>>;
+
 private:
 
     bool running = false;
@@ -143,13 +146,6 @@ private:
 
     void goalFinished(GoalPtr goal, Goal::WorkResult & f);
 
-    kj::Own<kj::PromiseFulfiller<void>> childFinished;
-
-    /**
-     * Wait for input to become available.
-     */
-    kj::Promise<Result<void>> waitForInput();
-
     /**
      * Remove a dead goal.
      */
@@ -160,11 +156,6 @@ private:
      */
     void childStarted(GoalPtr goal, kj::Promise<Result<Goal::WorkResult>> promise);
 
-    /**
-     * Unregisters a running child process.
-     */
-    void childTerminated(GoalPtr goal);
-
     /**
       * Pass current stats counters to the logger for progress bar updates.
       */
@@ -181,7 +172,7 @@ private:
         statisticsUpdateInhibitor = {};
     }
 
-    kj::Promise<Result<void>> runImpl();
+    kj::Promise<Result<void>> runImpl(Targets _topGoals);
     kj::Promise<Result<void>> boopGC(LocalStore & localStore);
 
 public:
@@ -197,7 +188,6 @@ public:
 
 private:
     kj::TaskSet children;
-    std::exception_ptr childException;
 
 public:
     struct HookState {
@@ -277,8 +267,6 @@ private:
     makeGoal(const DerivedPath & req, BuildMode buildMode = bmNormal) override;
 
 public:
-    using Targets = std::map<GoalPtr, kj::Promise<Result<Goal::WorkResult>>>;
-
     /**
      * Loop until the specified top-level goals have finished.
      */