From ec415d7166d607c92cf8f1af688f86e4b4731dff Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <edolstra@gmail.com>
Date: Fri, 2 Aug 2019 17:07:33 +0200
Subject: [PATCH] Add a test for auto-GC

This currently fails because we're using POSIX file locks. So when the
garbage collector opens and closes its own temproots file, it causes
the lock to be released and then deleted by another GC instance.
---
 src/libstore/gc.cc      |  9 +++++--
 src/libstore/globals.hh |  3 +++
 tests/gc-auto.sh        | 59 +++++++++++++++++++++++++++++++++++++++++
 tests/local.mk          |  4 ++-
 4 files changed, 72 insertions(+), 3 deletions(-)
 create mode 100644 tests/gc-auto.sh

diff --git a/src/libstore/gc.cc b/src/libstore/gc.cc
index 83cdf13a6..eeb237839 100644
--- a/src/libstore/gc.cc
+++ b/src/libstore/gc.cc
@@ -871,7 +871,12 @@ void LocalStore::collectGarbage(const GCOptions & options, GCResults & results)
 
 void LocalStore::autoGC(bool sync)
 {
-    auto getAvail = [this]() {
+    static auto fakeFreeSpaceFile = getEnv("_NIX_TEST_FREE_SPACE_FILE", "");
+
+    auto getAvail = [this]() -> uint64_t {
+        if (!fakeFreeSpaceFile.empty())
+            return std::stoll(readFile(fakeFreeSpaceFile));
+
         struct statvfs st;
         if (statvfs(realStoreDir.c_str(), &st))
             throw SysError("getting filesystem info about '%s'", realStoreDir);
@@ -892,7 +897,7 @@ void LocalStore::autoGC(bool sync)
 
         auto now = std::chrono::steady_clock::now();
 
-        if (now < state->lastGCCheck + std::chrono::seconds(5)) return;
+        if (now < state->lastGCCheck + std::chrono::seconds(settings.minFreeCheckInterval)) return;
 
         auto avail = getAvail();
 
diff --git a/src/libstore/globals.hh b/src/libstore/globals.hh
index 0af8215d1..0c0a9ec54 100644
--- a/src/libstore/globals.hh
+++ b/src/libstore/globals.hh
@@ -342,6 +342,9 @@ public:
     Setting<uint64_t> maxFree{this, std::numeric_limits<uint64_t>::max(), "max-free",
         "Stop deleting garbage when free disk space is above the specified amount."};
 
+    Setting<uint64_t> minFreeCheckInterval{this, 5, "min-free-check-interval",
+        "Number of seconds between checking free disk space."};
+
     Setting<Paths> pluginFiles{this, {}, "plugin-files",
         "Plugins to dynamically load at nix initialization time."};
 };
diff --git a/tests/gc-auto.sh b/tests/gc-auto.sh
new file mode 100644
index 000000000..1e91282d0
--- /dev/null
+++ b/tests/gc-auto.sh
@@ -0,0 +1,59 @@
+source common.sh
+
+clearStore
+
+garbage1=$(nix add-to-store --name garbage1 ./tarball.sh)
+garbage2=$(nix add-to-store --name garbage2 ./tarball.sh)
+garbage3=$(nix add-to-store --name garbage3 ./tarball.sh)
+
+fake_free=$TEST_ROOT/fake-free
+export _NIX_TEST_FREE_SPACE_FILE=$fake_free
+echo 1100 > $fake_free
+
+expr=$(cat <<EOF
+with import ./config.nix; mkDerivation {
+  name = "gc-A";
+  buildCommand = ''
+    [[ \$(ls \$NIX_STORE/*-garbage? | wc -l) = 3 ]]
+    mkdir \$out
+    echo foo > \$out/bar
+    echo 1...
+    sleep 2
+    echo 100 > $fake_free
+    echo 2...
+    sleep 2
+    echo 3...
+    [[ \$(ls \$NIX_STORE/*-garbage? | wc -l) = 1 ]]
+  '';
+}
+EOF
+)
+
+nix build -o $TEST_ROOT/result-A -L "($expr)" \
+    --min-free 1000 --max-free 2000 --min-free-check-interval 1 &
+pid=$!
+
+expr2=$(cat <<EOF
+with import ./config.nix; mkDerivation {
+  name = "gc-B";
+  buildCommand = ''
+    mkdir \$out
+    echo foo > \$out/bar
+    echo 1...
+    sleep 2
+    echo 100 > $fake_free
+    echo 2...
+    sleep 2
+    echo 3...
+  '';
+}
+EOF
+)
+
+nix build -o $TEST_ROOT/result-B -L "($expr2)" \
+    --min-free 1000 --max-free 2000 --min-free-check-interval 1
+
+wait "$pid"
+
+[[ foo = $(cat $TEST_ROOT/result-A/bar) ]]
+[[ foo = $(cat $TEST_ROOT/result-B/bar) ]]
diff --git a/tests/local.mk b/tests/local.mk
index 1ff68348b..261e4db0d 100644
--- a/tests/local.mk
+++ b/tests/local.mk
@@ -3,7 +3,9 @@ check:
 
 nix_tests = \
   init.sh hash.sh lang.sh add.sh simple.sh dependencies.sh \
-  gc.sh gc-concurrent.sh \
+  gc.sh \
+  gc-concurrent.sh \
+  gc-auto.sh \
   referrers.sh user-envs.sh logging.sh nix-build.sh misc.sh fixed.sh \
   gc-runtime.sh check-refs.sh filter-source.sh \
   remote-store.sh export.sh export-graph.sh \