Drop the dependency on libgc in libmain

Instead, libexpr now depends on libgc.  This means commands like
nix-store that don't do any evaluation no longer require libgc.

2 files changed, 22 insertions, 0 deletions

diff --git a/src/libexpr/Makefile.new b/src/libexpr/Makefile.new
index ded112107fe8..cbae11c53c20 100644
--- a/src/libexpr/Makefile.new
+++ b/src/libexpr/Makefile.new
@@ -9,6 +9,11 @@ libexpr_SOURCES = \
 
 libexpr_LIBS = libutil libstore libformat
 
+# The dependency on libgc must be propagated (i.e. meaning that
+# programs/libraries that use libexpr must explicitly pass -lgc),
+# because inline functions in libexpr's header files call libgc.
+libexpr_LDFLAGS_PROPAGATED = $(BDW_GC_LIBS)
+
 $(d)/parser-tab.cc $(d)/parser-tab.hh: $(d)/parser.y
 	bison -v -o $(libexpr_DIR)/parser-tab.cc $< -d
 
diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc
index e4a0d7fd2b3e..12c6aa8dcd44 100644
--- a/src/libexpr/eval.cc
+++ b/src/libexpr/eval.cc
@@ -129,6 +129,14 @@ string showType(const Value & v)
 }
 
 
+/* Called when the Boehm GC runs out of memory. */
+static void * oomHandler(size_t requested)
+{
+    /* Convert this to a proper C++ exception. */
+    throw std::bad_alloc();
+}
+
+
 EvalState::EvalState()
     : sWith(symbols.create("<with>"))
     , sOutPath(symbols.create("outPath"))
@@ -158,6 +166,14 @@ EvalState::EvalState()
 #if HAVE_BOEHMGC
     static bool gcInitialised = false;
     if (!gcInitialised) {
+
+        /* Initialise the Boehm garbage collector.  This isn't
+           necessary on most platforms, but for portability we do it
+           anyway. */
+        GC_INIT();
+
+        GC_oom_fn = oomHandler;
+
         /* Set the initial heap size to something fairly big (25% of
            physical RAM, up to a maximum of 384 MiB) so that in most
            cases we don't need to garbage collect at all.  (Collection
@@ -181,6 +197,7 @@ EvalState::EvalState()
             debug(format("setting initial heap size to %1% bytes") % size);
             GC_expand_hp(size);
         }
+
         gcInitialised = true;
     }
 #endif