libstore: remove worker removeGoal

this was immensely inefficient on large caches, as can exist when many
derivations are buildable simultaneously. since we have smart pointers
to goals we can do cache maintenance in goal deleters instead, and use
the exact iterators instead of doing a linear search. this *does* rely
on goals being deleted to remove them from the cache, which isn't true
for toplevel goals. those would have previously been removed when done
in all cases, removing the cache entry when keep-going is set. this is
arguably incorrect since it might result in those goals being retried,
although that could only happen with dynamic derivations or the likes.
(luckily dynamic derivations not complete enough to allow this at all)

Change-Id: I8e750b868393588c33e4829333d370f2c509ce99

2 files changed, 28 insertions, 43 deletions

diff --git a/src/libstore/build/worker.cc b/src/libstore/build/worker.cc
index b1adf6d10..94a638725 100644
--- a/src/libstore/build/worker.cc
+++ b/src/libstore/build/worker.cc
@@ -65,7 +65,26 @@ std::pair<std::shared_ptr<G>, kj::Promise<void>> Worker::makeGoalCommon(
     auto & goal_weak = it->second;
     auto goal = goal_weak.goal.lock();
     if (!goal) {
-        goal = create();
+        struct Deleter
+        {
+            std::map<ID, CachedGoal<G>> * from;
+            std::map<ID, CachedGoal<G>>::const_iterator iter;
+
+            void operator()(G * g)
+            {
+                from->erase(iter);
+                delete g;
+            }
+        };
+
+        // this dance is necessary to be memory-safe in exceptional cases.
+        // if *anything* here throws we must still delete the goal object.
+        goal = [&] {
+            std::unique_ptr<G, Deleter> tmp(nullptr, Deleter{&map, it});
+            tmp.reset(create().release());
+            return tmp;
+        }();
+
         goal->notify = std::move(goal_weak.fulfiller);
         goal_weak.goal = goal;
         wakeUp(goal);
@@ -165,21 +184,6 @@ std::pair<GoalPtr, kj::Promise<void>> Worker::makeGoal(const DerivedPath & req,
 }
 
 
-template<typename G>
-static void removeGoal(std::shared_ptr<G> goal, auto & goalMap)
-{
-    /* !!! inefficient */
-    for (auto i = goalMap.begin();
-         i != goalMap.end(); )
-        if (i->second.goal.lock() == goal) {
-            auto j = i; ++j;
-            goalMap.erase(i);
-            i = j;
-        }
-        else ++i;
-}
-
-
 void Worker::goalFinished(GoalPtr goal, Goal::Finished & f)
 {
     goal->trace("done");
@@ -192,9 +196,16 @@ void Worker::goalFinished(GoalPtr goal, Goal::Finished & f)
     hashMismatch |= f.hashMismatch;
     checkMismatch |= f.checkMismatch;
 
-    removeGoal(goal);
     goal->notify->fulfill();
     goal->cleanup();
+
+    if (topGoals.find(goal) != topGoals.end()) {
+        topGoals.erase(goal);
+        /* If a top-level goal failed, then kill all other goals
+           (unless keepGoing was set). */
+        if (goal->exitCode == Goal::ecFailed && !settings.keepGoing)
+            topGoals.clear();
+    }
 }
 
 void Worker::handleWorkResult(GoalPtr goal, Goal::WorkResult how)
@@ -210,27 +221,6 @@ void Worker::handleWorkResult(GoalPtr goal, Goal::WorkResult how)
     updateStatistics();
 }
 
-void Worker::removeGoal(GoalPtr goal)
-{
-    if (auto drvGoal = std::dynamic_pointer_cast<DerivationGoal>(goal))
-        nix::removeGoal(drvGoal, derivationGoals);
-    else if (auto subGoal = std::dynamic_pointer_cast<PathSubstitutionGoal>(goal))
-        nix::removeGoal(subGoal, substitutionGoals);
-    else if (auto subGoal = std::dynamic_pointer_cast<DrvOutputSubstitutionGoal>(goal))
-        nix::removeGoal(subGoal, drvOutputSubstitutionGoals);
-    else
-        assert(false);
-
-    if (topGoals.find(goal) != topGoals.end()) {
-        topGoals.erase(goal);
-        /* If a top-level goal failed, then kill all other goals
-           (unless keepGoing was set). */
-        if (goal->exitCode == Goal::ecFailed && !settings.keepGoing)
-            topGoals.clear();
-    }
-}
-
-
 void Worker::wakeUp(GoalPtr goal)
 {
     goal->trace("woken up");
diff --git a/src/libstore/build/worker.hh b/src/libstore/build/worker.hh
index 1953bbec1..fb68a0ef3 100644
--- a/src/libstore/build/worker.hh
+++ b/src/libstore/build/worker.hh
@@ -159,11 +159,6 @@ private:
     void waitForInput();
 
     /**
-     * Remove a dead goal.
-     */
-    void removeGoal(GoalPtr goal);
-
-    /**
      * Registers a running child process.
      */
     void childStarted(GoalPtr goal, kj::Promise<Result<Goal::WorkResult>> promise);