NixOS · Apr 15, 2019 · Apr 22, 2019 · Apr 22, 2019 · Apr 22, 2019 · Apr 23, 2019
diff --git a/src/libexpr/attr-path.cc b/src/libexpr/attr-path.cc
@@ -32,15 +32,15 @@ static Strings parseAttrPath(const string & s)
 }
 
 
-Value * findAlongAttrPath(EvalState & state, const string & attrPath,
+Ptr<Value> findAlongAttrPath(EvalState & state, const string & attrPath,
     Bindings & autoArgs, Value & vIn)
 {
     Strings tokens = parseAttrPath(attrPath);
 
     Error attrError =
         Error(format("attribute selection path '%1%' does not match expression") % attrPath);
 
-    Value * v = &vIn;
+    Ptr<Value> v(&vIn);
 
     for (auto & attr : tokens) {
 
@@ -50,7 +50,7 @@ Value * findAlongAttrPath(EvalState & state, const string & attrPath,
         if (string2Int(attr, attrIndex)) apType = apIndex;
 
         /* Evaluate the expression. */
-        Value * vNew = state.allocValue();
+        auto vNew = state.allocValue();
         state.autoCallFunction(autoArgs, *v, *vNew);
         v = vNew;
         state.forceValue(*v);
@@ -71,7 +71,7 @@ Value * findAlongAttrPath(EvalState & state, const string & attrPath,
             Bindings::iterator a = v->attrs->find(state.symbols.create(attr));
             if (a == v->attrs->end())
                 throw Error(format("attribute '%1%' in selection path '%2%' not found") % attr % attrPath);
-            v = &*a->value;
+            v = a->value;
         }
 
         else if (apType == apIndex) {

diff --git a/src/libexpr/attr-path.hh b/src/libexpr/attr-path.hh
@@ -7,7 +7,7 @@
 
 namespace nix {
 
-Value * findAlongAttrPath(EvalState & state, const string & attrPath,
+Ptr<Value> findAlongAttrPath(EvalState & state, const string & attrPath,
     Bindings & autoArgs, Value & vIn);
 
 }
diff --git a/src/libexpr/attr-set.cc b/src/libexpr/attr-set.cc
@@ -7,28 +7,28 @@
 namespace nix {
 
 
-/* Allocate a new array of attributes for an attribute set with a specific
-   capacity. The space is implicitly reserved after the Bindings
-   structure. */
-Bindings * EvalState::allocBindings(size_t capacity)
+/* Allocate a new array of attributes for an attribute set with a
+   specific capacity. The space is implicitly reserved after the
+   Bindings structure. */
+Ptr<Bindings> Bindings::allocBindings(size_t capacity)
 {
-    if (capacity > std::numeric_limits<Bindings::size_t>::max())
+    if (capacity >= 1UL << Object::miscBytes * 8)
         throw Error("attribute set of size %d is too big", capacity);
-    return new (allocBytes(sizeof(Bindings) + sizeof(Attr) * capacity)) Bindings((Bindings::size_t) capacity);
+    return gc.alloc<Bindings>(Bindings::wordsFor(capacity), capacity);
 }
 
 
 void EvalState::mkAttrs(Value & v, size_t capacity)
 {
     if (capacity == 0) {
-        v = vEmptySet;
-        return;
+        v.attrs = emptyBindings;
+        v.type = tAttrs;
+    } else {
+        v.attrs = Bindings::allocBindings(capacity);
+        v.type = tAttrs;
+        nrAttrsets++;
+        nrAttrsInAttrsets += capacity;
     }
-    clearValue(v);
-    v.type = tAttrs;
-    v.attrs = allocBindings(capacity);
-    nrAttrsets++;
-    nrAttrsInAttrsets += capacity;
 }
 
 
@@ -37,7 +37,7 @@ void EvalState::mkAttrs(Value & v, size_t capacity)
    this attribute. */
 Value * EvalState::allocAttr(Value & vAttrs, const Symbol & name)
 {
-    Value * v = allocValue();
+    auto v = allocValue();
     vAttrs.attrs->push_back(Attr(name, v));
     return v;
 }

diff --git a/src/libexpr/attr-set.hh b/src/libexpr/attr-set.hh
@@ -2,6 +2,7 @@
 
 #include "nixexpr.hh"
 #include "symbol-table.hh"
+#include "gc.hh"
 
 #include <algorithm>
 
@@ -30,19 +31,22 @@ struct Attr
    by its size and its capacity, the capacity being the number of Attr
    elements allocated after this structure, while the size corresponds to
    the number of elements already inserted in this structure. */
-class Bindings
+class Bindings : public Object
 {
 public:
     typedef uint32_t size_t;
 
 private:
-    size_t size_, capacity_;
+    // FIXME: eliminate size_. We can just rely on capacity by sorting
+    // null entries towards the end of the vector.
+    size_t size_;
     Attr attrs[0];
 
-    Bindings(size_t capacity) : size_(0), capacity_(capacity) { }
+    Bindings(size_t capacity) : Object(tBindings, capacity), size_(0) {}
     Bindings(const Bindings & bindings) = delete;
 
 public:
+
     size_t size() const { return size_; }
 
     bool empty() const { return !size_; }
@@ -51,7 +55,8 @@ public:
 
     void push_back(const Attr & attr)
     {
-        assert(size_ < capacity_);
+        assert(size_ < capacity());
+        gc.assertObject(attr.value);
         attrs[size_++] = attr;
     }
 
@@ -73,7 +78,7 @@ public:
 
     void sort();
 
-    size_t capacity() { return capacity_; }
+    size_t capacity() const { return getMisc(); }
 
     /* Returns the attributes in lexicographically sorted order. */
     std::vector<const Attr *> lexicographicOrder() const
@@ -88,7 +93,19 @@ public:
         return res;
     }
 
-    friend class EvalState;
+    size_t words() const
+    {
+        return wordsFor(capacity());
+    }
+
+    static size_t wordsFor(size_t capacity)
+    {
+        return 2 + 3 * capacity; // FIXME
+    }
+
+    static Ptr<Bindings> allocBindings(size_t capacity);
+
+    friend class GC;
 };
 
 

diff --git a/src/libexpr/common-eval-args.cc b/src/libexpr/common-eval-args.cc
@@ -28,9 +28,9 @@ MixEvalArgs::MixEvalArgs()
         .handler([&](std::string s) { searchPath.push_back(s); });
 }
 
-Bindings * MixEvalArgs::getAutoArgs(EvalState & state)
+Ptr<Bindings> MixEvalArgs::getAutoArgs(EvalState & state)
 {
-    Bindings * res = state.allocBindings(autoArgs.size());
+    auto res = Bindings::allocBindings(autoArgs.size());
     for (auto & i : autoArgs) {
         Value * v = state.allocValue();
         if (i.second[0] == 'E')

diff --git a/src/libexpr/common-eval-args.hh b/src/libexpr/common-eval-args.hh
@@ -8,11 +8,14 @@ class Store;
 class EvalState;
 class Bindings;
 
+template<class T>
+struct Ptr;
+
 struct MixEvalArgs : virtual Args
 {
     MixEvalArgs();
 
-    Bindings * getAutoArgs(EvalState & state);
+    Ptr<Bindings> getAutoArgs(EvalState & state);
 
     Strings searchPath;
 

diff --git a/src/libexpr/eval-inline.hh b/src/libexpr/eval-inline.hh
@@ -27,21 +27,27 @@ LocalNoInlineNoReturn(void throwTypeError(const char * s, const Value & v, const
 void EvalState::forceValue(Value & v, const Pos & pos)
 {
     if (v.type == tThunk) {
-        Env * env = v.thunk.env;
+        // FIXME: this is necessary because some values (like vList2)
+        // are created non-atomically.
+        Ptr<Env> env(v.thunk.env);
         Expr * expr = v.thunk.expr;
         try {
             v.type = tBlackhole;
             //checkInterrupt();
             expr->eval(*this, *env, v);
         } catch (...) {
-            v.type = tThunk;
             v.thunk.env = env;
             v.thunk.expr = expr;
+            v.type = tThunk;
             throw;
         }
     }
-    else if (v.type == tApp)
+    else if (v.type == tApp) {
+        // FIXME: idem.
+        Ptr<Value> left(v.app.left);
+        Ptr<Value> right(v.app.right);
         callFunction(*v.app.left, *v.app.right, v, noPos);
+    }
     else if (v.type == tBlackhole)
         throwEvalError("infinite recursion encountered, at %1%", pos);
 }
@@ -78,18 +84,5 @@ inline void EvalState::forceList(Value & v, const Pos & pos)
         throwTypeError("value is %1% while a list was expected, at %2%", v, pos);
 }
 
-/* Note: Various places expect the allocated memory to be zeroed. */
-inline void * allocBytes(size_t n)
-{
-    void * p;
-#if HAVE_BOEHMGC
-    p = GC_MALLOC(n);
-#else
-    p = calloc(n, 1);
-#endif
-    if (!p) throw std::bad_alloc();
-    return p;
-}
-
 
 }