Reduce substitution memory consumption

copyStorePath() now pipes the output of srcStore->narFromPath()
directly into dstStore->addToStore(). The sink used by the former is
converted into a source usable by the latter using
boost::coroutine2. This is based on [1].

This reduces the maximum resident size of

  $ nix build --store ~/my-nix/ /nix/store/b0zlxla7dmy1iwc3g459rjznx59797xy-binutils-2.28.1 --substituters file:///tmp/binary-cache-xz/ --no-require-sigs

from 418592 KiB to 53416 KiB. (The previous commit also reduced the
runtime from ~4.2s to ~3.4s, not sure why.) A further improvement will
be to download files into a Sink.

[1] https://github.com/NixOS/nix/compare/master...Mathnerd314:dump-fix-coroutine#diff-dcbcac55a634031f9cc73707da6e4b18

Issue #1969.

1 files changed, 6 insertions, 1 deletions

diff --git a/src/libstore/store-api.hh b/src/libstore/store-api.hh
index 563aa566bd37..ea259f07e8ab 100644
--- a/src/libstore/store-api.hh
+++ b/src/libstore/store-api.hh
@@ -399,9 +399,14 @@ public:
     virtual bool wantMassQuery() { return false; }
 
     /* Import a path into the store. */
+    virtual void addToStore(const ValidPathInfo & info, Source & narSource,
+        RepairFlag repair = NoRepair, CheckSigsFlag checkSigs = CheckSigs,
+        std::shared_ptr<FSAccessor> accessor = 0);
+
+    // FIXME: remove
     virtual void addToStore(const ValidPathInfo & info, const ref<std::string> & nar,
         RepairFlag repair = NoRepair, CheckSigsFlag checkSigs = CheckSigs,
-        std::shared_ptr<FSAccessor> accessor = 0) = 0;
+        std::shared_ptr<FSAccessor> accessor = 0);
 
     /* Copy the contents of a path to the store and register the
        validity the resulting path.  The resulting path is returned.