libstore: turn periodic gc attempt into a promise

notably we will check whether we want to do GC at all only once during
startup, and we'll only attempt GC every ten seconds rather than every
time a goal has finished a partial work call. this shouldn't cause any
problems in practice since relying on auto-gc is not deterministic and
stores in which builds can fill all remaining free space in merely ten
seconds are severely troubled even when gargage collection runs a lot.

Change-Id: I1175a56bf7f4e531f8be90157ad88750ff2ddec4

1 files changed, 2 insertions, 0 deletions

diff --git a/src/libstore/build/worker.hh b/src/libstore/build/worker.hh
index 6da76fe34..dc85c43e3 100644
--- a/src/libstore/build/worker.hh
+++ b/src/libstore/build/worker.hh
@@ -20,6 +20,7 @@ namespace nix {
 struct DerivationGoal;
 struct PathSubstitutionGoal;
 class DrvOutputSubstitutionGoal;
+class LocalStore;
 
 typedef std::chrono::time_point<std::chrono::steady_clock> steady_time_point;
 
@@ -189,6 +190,7 @@ private:
     }
 
     kj::Promise<Result<void>> runImpl();
+    kj::Promise<Result<void>> boopGC(LocalStore & localStore);
 
 public: