From fec5acd7ece89e6b5ba36c2e612628103d329dfc Mon Sep 17 00:00:00 2001
From: aravind <aravind@fb.com>
Date: Tue, 21 May 2013 12:39:07 -0700
Subject: [PATCH] Treadmill for shared variants

Avoids atomic incRefs and decRefs. StringData no longer needs to
be sweepable for SharedVariants.
---
 hphp/runtime/base/array/array_data.h          |  2 -
 hphp/runtime/base/array/policy_array.h        |  4 --
 hphp/runtime/base/execution_context.h         |  6 +++
 hphp/runtime/base/memory/memory_manager.cpp   |  2 -
 hphp/runtime/base/memory/memory_manager.h     |  1 -
 .../base/shared/concurrent_shared_store.cpp   | 22 ++++------
 hphp/runtime/base/shared/immutable_map.cpp    |  8 ++--
 hphp/runtime/base/shared/immutable_map.h      |  3 +-
 hphp/runtime/base/shared/immutable_obj.cpp    |  2 +-
 hphp/runtime/base/shared/shared_map.cpp       |  1 -
 hphp/runtime/base/shared/shared_map.h         | 11 +----
 hphp/runtime/base/shared/shared_variant.cpp   | 13 +-----
 hphp/runtime/base/shared/shared_variant.h     | 32 +++-----------
 hphp/runtime/base/string_data.cpp             | 43 -------------------
 hphp/runtime/base/string_data.h               | 14 +-----
 hphp/runtime/base/type_variant.cpp            | 13 ------
 hphp/runtime/base/type_variant.h              |  5 ---
 hphp/runtime/vm/bytecode.cpp                  | 22 ++++++++++
 18 files changed, 51 insertions(+), 153 deletions(-)

diff --git a/hphp/runtime/base/array/array_data.h b/hphp/runtime/base/array/array_data.h
index 04d47d364..c015c61ac 100644
--- a/hphp/runtime/base/array/array_data.h
+++ b/hphp/runtime/base/array/array_data.h
@@ -177,8 +177,6 @@ class ArrayData : public Countable {
    */
   virtual bool isVectorData() const;
 
-  virtual SharedVariant *getSharedVariant() const { return nullptr; }
-
   /**
    * Whether or not this array has a referenced Variant or Object appearing
    * twice. This is mainly for APC to decide whether to serialize an array.
diff --git a/hphp/runtime/base/array/policy_array.h b/hphp/runtime/base/array/policy_array.h
index e3ced33ca..0b706cc34 100644
--- a/hphp/runtime/base/array/policy_array.h
+++ b/hphp/runtime/base/array/policy_array.h
@@ -374,10 +374,6 @@ public:
    */
   virtual bool isVectorData() const FOLLY_OVERRIDE;
 
-  virtual SharedVariant *getSharedVariant() const FOLLY_OVERRIDE {
-    return nullptr;
-  }
-
   /**
    * Position-based iterations.
    */
diff --git a/hphp/runtime/base/execution_context.h b/hphp/runtime/base/execution_context.h
index 097372445..000466293 100644
--- a/hphp/runtime/base/execution_context.h
+++ b/hphp/runtime/base/execution_context.h
@@ -411,6 +411,8 @@ private:
   DECLARE_DBG_SETTING
 };
 
+typedef std::vector<SharedVariant*> SVarVector;
+
 class VMExecutionContext : public BaseExecutionContext {
 public:
   VMExecutionContext();
@@ -445,8 +447,12 @@ public:
   static void unpackContVarEnvLinkage(ActRec* fp);
   static void packContVarEnvLinkage(ActRec* fp);
   void pushLocalsAndIterators(const HPHP::Func* f, int nparams = 0);
+  void enqueueSharedVar(SharedVariant* var);
 
 private:
+  SVarVector m_freedSvars;
+  void treadmillSharedVars();
+
   enum VectorLeaveCode {
     ConsumeAll,
     LeaveLast
diff --git a/hphp/runtime/base/memory/memory_manager.cpp b/hphp/runtime/base/memory/memory_manager.cpp
index d458ac449..2105fe55e 100644
--- a/hphp/runtime/base/memory/memory_manager.cpp
+++ b/hphp/runtime/base/memory/memory_manager.cpp
@@ -169,7 +169,6 @@ MemoryManager::MemoryManager() : m_front(0), m_limit(0),
   m_stats.maxBytes = INT64_MAX;
   // make the circular-lists empty.
   m_sweep.next = m_sweep.prev = &m_sweep;
-  m_strings.next = m_strings.prev = &m_strings;
 }
 
 void MemoryManager::resetStats() {
@@ -222,7 +221,6 @@ struct SmallNode {
 typedef std::vector<char*>::const_iterator SlabIter;
 
 void MemoryManager::rollback() {
-  StringData::sweepAll();
   for (unsigned int i = 0, n = m_smartAllocators.size(); i < n; i++) {
     m_smartAllocators[i]->clear();
   }
diff --git a/hphp/runtime/base/memory/memory_manager.h b/hphp/runtime/base/memory/memory_manager.h
index 823dc7f21..8ea0b4058 100644
--- a/hphp/runtime/base/memory/memory_manager.h
+++ b/hphp/runtime/base/memory/memory_manager.h
@@ -349,7 +349,6 @@ private:
   char *m_front, *m_limit;
   GarbageList m_smartfree[kNumSizes];
   SweepNode m_sweep;   // oversize smart_malloc'd blocks
-  SweepNode m_strings; // in-place node is head of circular list
   MemoryUsageStats m_stats;
   bool m_enabled;
 
diff --git a/hphp/runtime/base/shared/concurrent_shared_store.cpp b/hphp/runtime/base/shared/concurrent_shared_store.cpp
index 3a119613b..16355f1fd 100644
--- a/hphp/runtime/base/shared/concurrent_shared_store.cpp
+++ b/hphp/runtime/base/shared/concurrent_shared_store.cpp
@@ -106,7 +106,7 @@ bool ConcurrentTableSharedStore::clear() {
   for (Map::iterator iter = m_vars.begin(); iter != m_vars.end();
        ++iter) {
     if (iter->second.inMem()) {
-      iter->second.var->decRef();
+      g_vmContext->enqueueSharedVar(iter->second.var);
     }
     free((void *)iter->first);
   }
@@ -132,7 +132,7 @@ bool ConcurrentTableSharedStore::eraseImpl(CStrRef key, bool expired) {
     }
     if (acc->second.inMem()) {
       stats_on_delete(key.get(), &acc->second, expired);
-      acc->second.var->decRef();
+      g_vmContext->enqueueSharedVar(acc->second.var);
     } else {
       assert(acc->second.inFile());
       assert(acc->second.expiry == 0);
@@ -215,7 +215,7 @@ bool ConcurrentTableSharedStore::handlePromoteObj(CStrRef key,
     if (!m_vars.find(acc, key.data())) {
       // There is a chance another thread deletes the key when this thread is
       // converting the object. In that case, we just bail
-      converted->decRef();
+      delete converted;
       return false;
     }
     // A write lock was acquired during find
@@ -227,10 +227,10 @@ bool ConcurrentTableSharedStore::handlePromoteObj(CStrRef key,
       int64_t ttl = sval->expiry ? sval->expiry - time(nullptr) : 0;
       stats_on_update(key.get(), sval, converted, ttl);
       sval->var = converted;
-      sv->decRef();
+      g_vmContext->enqueueSharedVar(sv);
       return true;
     }
-    converted->decRef();
+    delete converted;
   }
   return false;
 }
@@ -295,8 +295,6 @@ bool ConcurrentTableSharedStore::get(CStrRef key, Variant &value) {
         }
 
         if (RuntimeOption::ApcAllowObj && svar->is(KindOfObject)) {
-          // Hold ref here for later promoting the object
-          svar->incRef();
           promoteObj = true;
         }
         value = svar->toLocal();
@@ -313,8 +311,6 @@ bool ConcurrentTableSharedStore::get(CStrRef key, Variant &value) {
 
   if (promoteObj)  {
     handlePromoteObj(key, svar, value);
-    // release the extra ref
-    svar->decRef();
   }
   return true;
 }
@@ -344,7 +340,7 @@ int64_t ConcurrentTableSharedStore::inc(CStrRef key, int64_t step, bool &found)
       if (!sval->expired()) {
         ret = get_int64_value(sval) + step;
         SharedVariant *svar = construct(Variant(ret));
-        sval->var->decRef();
+        g_vmContext->enqueueSharedVar(sval->var);
         sval->var = svar;
         found = true;
         log_apc(std_apc_hit);
@@ -365,7 +361,7 @@ bool ConcurrentTableSharedStore::cas(CStrRef key, int64_t old, int64_t val) {
       sval = &acc->second;
       if (!sval->expired() && get_int64_value(sval) == old) {
         SharedVariant *var = construct(Variant(val));
-        sval->var->decRef();
+        g_vmContext->enqueueSharedVar(sval->var);
         sval->var = var;
         success = true;
         log_apc(std_apc_cas);
@@ -440,7 +436,7 @@ bool ConcurrentTableSharedStore::store(CStrRef key, CVarRef value, int64_t ttl,
         if (sval->inMem()) {
           stats_on_update(key.get(), sval, svar,
                           adjust_ttl(ttl, overwritePrime));
-          sval->var->decRef();
+          g_vmContext->enqueueSharedVar(sval->var);
           update = true;
         } else {
           // mark the inFile copy invalid since we are updating the key
@@ -448,7 +444,7 @@ bool ConcurrentTableSharedStore::store(CStrRef key, CVarRef value, int64_t ttl,
           sval->sSize = 0;
         }
       } else {
-        svar->decRef();
+        delete svar;
         return false;
       }
     }
diff --git a/hphp/runtime/base/shared/immutable_map.cpp b/hphp/runtime/base/shared/immutable_map.cpp
index e36f46c72..5f63ef71c 100644
--- a/hphp/runtime/base/shared/immutable_map.cpp
+++ b/hphp/runtime/base/shared/immutable_map.cpp
@@ -24,8 +24,7 @@ namespace HPHP {
 
 HOT_FUNC
 ImmutableMap* ImmutableMap::Create(ArrayData* arr,
-                                   bool unserializeObj,
-                                   bool &shouldCache) {
+                                   bool unserializeObj) {
   int num = arr->size();
   int cap = num > 2 ? Util::roundUpToPowerOfTwo(num) : 2;
 
@@ -43,7 +42,6 @@ ImmutableMap* ImmutableMap::Create(ArrayData* arr,
                                                  unserializeObj);
       SharedVariant* val = SharedVariant::Create(it.secondRef(), false, true,
                                                  unserializeObj);
-      if (val->m_shouldCache) shouldCache = true;
       ret->add(ret->m.m_num, key, val);
       ++ret->m.m_num;
     }
@@ -59,8 +57,8 @@ HOT_FUNC
 void ImmutableMap::Destroy(ImmutableMap* map) {
   Bucket* buckets = map->buckets();
   for (int i = 0; i < map->m.m_num; i++) {
-    buckets[i].key->decRef();
-    buckets[i].val->decRef();
+    delete buckets[i].key;
+    delete buckets[i].val;
   }
   free(map);
 }
diff --git a/hphp/runtime/base/shared/immutable_map.h b/hphp/runtime/base/shared/immutable_map.h
index 291b005b6..2ee3e62b0 100644
--- a/hphp/runtime/base/shared/immutable_map.h
+++ b/hphp/runtime/base/shared/immutable_map.h
@@ -63,8 +63,7 @@ public:
   }
 
   static ImmutableMap* Create(ArrayData* arr,
-                              bool unserializeObj,
-                              bool& shouldCache);
+                              bool unserializeObj);
   static void Destroy(ImmutableMap* im);
 private:
   ImmutableMap() {}
diff --git a/hphp/runtime/base/shared/immutable_obj.cpp b/hphp/runtime/base/shared/immutable_obj.cpp
index 94fa26bd1..9f23bbb66 100644
--- a/hphp/runtime/base/shared/immutable_obj.cpp
+++ b/hphp/runtime/base/shared/immutable_obj.cpp
@@ -82,7 +82,7 @@ ImmutableObj::~ImmutableObj() {
   if (m_props) {
     for (int i = 0; i < m_propCount; i++) {
       m_props[i].name->destruct();
-      if (m_props[i].val) m_props[i].val->decRef();
+      if (m_props[i].val) delete m_props[i].val;
     }
     free(m_props);
   }
diff --git a/hphp/runtime/base/shared/shared_map.cpp b/hphp/runtime/base/shared/shared_map.cpp
index 18af36e89..ad902c793 100644
--- a/hphp/runtime/base/shared/shared_map.cpp
+++ b/hphp/runtime/base/shared/shared_map.cpp
@@ -54,7 +54,6 @@ SharedMap::~SharedMap() {
     }
     smart_free(m_localCache);
   }
-  m_arr->decRef();
 }
 
 bool SharedMap::exists(const StringData* k) const {
diff --git a/hphp/runtime/base/shared/shared_map.h b/hphp/runtime/base/shared/shared_map.h
index f48aa4f99..7254f9f66 100644
--- a/hphp/runtime/base/shared/shared_map.h
+++ b/hphp/runtime/base/shared/shared_map.h
@@ -29,24 +29,18 @@ namespace HPHP {
 /**
  * Wrapper for a shared memory map.
  */
-class SharedMap : public ArrayData, Sweepable {
+class SharedMap : public ArrayData {
 public:
   SharedMap(SharedVariant* source)
     : ArrayData(kSharedMap)
     , m_arr(source)
     , m_localCache(nullptr) {
-    source->incRef();
   }
 
   ~SharedMap();
 
   virtual bool isSharedMap() const { return true; }
 
-  virtual SharedVariant *getSharedVariant() const {
-    if (m_arr->shouldCache()) return nullptr;
-    return m_arr;
-  }
-
   // these using directives ensure the full set of overloaded functions
   // are visible in this class, to avoid triggering implicit conversions
   // from a CVarRef key to int64.
@@ -122,9 +116,6 @@ public:
    */
   DECLARE_SMART_ALLOCATION(SharedMap);
 
-  // implements Sweepable.sweep()
-  void sweep() { m_arr->decRef(); }
-
   virtual ArrayData *escalate() const;
   virtual ArrayData* escalateForSort();
 
diff --git a/hphp/runtime/base/shared/shared_variant.cpp b/hphp/runtime/base/shared/shared_variant.cpp
index ca001f02f..d8b81af9c 100644
--- a/hphp/runtime/base/shared/shared_variant.cpp
+++ b/hphp/runtime/base/shared/shared_variant.cpp
@@ -26,7 +26,7 @@ namespace HPHP {
 SharedVariant::SharedVariant(CVarRef source, bool serialized,
                              bool inner /* = false */,
                              bool unserializeObj /* = false */)
-  : m_shouldCache(false), m_flags(0) {
+  : m_flags(0) {
   assert(!serialized || source.isString());
   m_count = 1;
   m_type = source.getType();
@@ -81,7 +81,6 @@ StringCase:
         PointerSet seen;
         if (arr->hasInternalReference(seen)) {
           setSerializedArray();
-          m_shouldCache = true;
           String s = apc_serialize(source);
           m_data.str = new StringData(s.data(), s.size(), CopyMalloc);
           break;
@@ -94,11 +93,10 @@ StringCase:
         for (ArrayIter it(arr); !it.end(); it.next()) {
           SharedVariant* val = Create(it.secondRef(), false, true,
                                       unserializeObj);
-          if (val->m_shouldCache) m_shouldCache = true;
           m_data.vec->vals()[m_data.vec->m_size++] = val;
         }
       } else {
-        m_data.map = ImmutableMap::Create(arr, unserializeObj, m_shouldCache);
+        m_data.map = ImmutableMap::Create(arr, unserializeObj);
       }
       break;
     }
@@ -110,7 +108,6 @@ StringCase:
   default:
     {
       assert(source.isObject());
-      m_shouldCache = true;
       if (unserializeObj) {
         // This assumes hasInternalReference(seen, true) is false
         ImmutableObj* obj = new ImmutableObj(source.getObjectData());
@@ -328,12 +325,6 @@ int SharedVariant::countReachable() const {
 SharedVariant *SharedVariant::Create
 (CVarRef source, bool serialized, bool inner /* = false */,
  bool unserializeObj /* = false*/) {
-  SharedVariant *wrapped = source.getSharedVariant();
-  if (wrapped && !unserializeObj) {
-    wrapped->incRef();
-    // static cast should be enough
-    return (SharedVariant *)wrapped;
-  }
   return new SharedVariant(source, serialized, inner, unserializeObj);
 }
 
diff --git a/hphp/runtime/base/shared/shared_variant.h b/hphp/runtime/base/shared/shared_variant.h
index 39423d4bf..e7e8be3d7 100644
--- a/hphp/runtime/base/shared/shared_variant.h
+++ b/hphp/runtime/base/shared/shared_variant.h
@@ -59,29 +59,11 @@ public:
   DataType getType() const { return (DataType)m_type; }
   CVarRef asCVarRef() const {
     // Must be non-refcounted types
-    assert(m_shouldCache == false);
     assert(m_flags == 0);
     assert(!IS_REFCOUNTED_TYPE(m_tv.m_type));
     return tvAsCVarRef(&m_tv);
   }
 
-  void incRef() {
-    assert(IS_REFCOUNTED_TYPE(m_type));
-    atomic_inc(m_count);
-  }
-
-  void decRef() {
-    assert(m_count);
-    if (IS_REFCOUNTED_TYPE(m_type)) {
-      if (atomic_dec(m_count) == 0) {
-        delete this;
-      }
-    } else {
-      assert(m_count == 1);
-      delete this;
-    }
-  }
-
   Variant toLocal();
 
   int64_t intData() const {
@@ -139,7 +121,6 @@ public:
 
   SharedVariant *convertObj(CVarRef var);
   bool isUnserializedObj() { return getIsObj(); }
-  bool shouldCache() const { return m_shouldCache; }
 
   int countReachable() const;
 
@@ -156,7 +137,7 @@ private:
     ~VectorData() {
       SharedVariant** v = vals();
       for (size_t i = 0; i < m_size; i++) {
-        v[i]->decRef();
+        delete v[i];
       }
     }
     SharedVariant** vals() { return (SharedVariant**)(this + 1); }
@@ -172,7 +153,7 @@ private:
   /*
    * Keep the object layout binary compatible with Variant for primitive types.
    * We want to have compile time assertion to guard it but still want to have
-   * anonymous struct. For non-refcounted types, m_shouldCache and m_flags are
+   * anonymous struct. For non-refcounted types, m_flags is
    * guaranteed to be 0, and other parts of runtime will not touch the count.
    */
 
@@ -191,23 +172,20 @@ private:
 #if PACKED_TV
       uint8_t _typePad;
       DataType m_type;
-      bool m_shouldCache;
-      uint8_t m_flags;
+      uint16_t m_flags;
       uint32_t m_count;
       SharedData m_data;
 #else
  #ifdef WORDS_BIGENDIAN
       SharedData m_data;
       uint32_t m_count;
-      bool m_shouldCache;
-      uint8_t m_flags;
+      uint16_t m_flags;
       uint16_t m_type;
  #else
       SharedData m_data;
       uint32_t m_count;
       uint16_t m_type;
-      bool m_shouldCache;
-      uint8_t m_flags;
+      uint16_t m_flags;
  #endif
 #endif
     };
diff --git a/hphp/runtime/base/string_data.cpp b/hphp/runtime/base/string_data.cpp
index 6fa058607..49d6e052f 100644
--- a/hphp/runtime/base/string_data.cpp
+++ b/hphp/runtime/base/string_data.cpp
@@ -212,41 +212,6 @@ void StringData::initLiteral(const char* data, int len) {
   assert(checkSane());
 }
 
-void StringData::enlist() {
-  assert(isShared());
-  SweepNode& head = MemoryManager::TheMemoryManager()->m_strings;
-  // insert after head
-  SweepNode* next = head.next;
-  assert(uintptr_t(next) != kMallocFreeWord);
-  m_big.node.next = next;
-  m_big.node.prev = &head;
-  next->prev = head.next = &m_big.node;
-}
-
-void StringData::delist() {
-  assert(isShared());
-  SweepNode* next = m_big.node.next;
-  SweepNode* prev = m_big.node.prev;
-  assert(uintptr_t(next) != kMallocFreeWord);
-  assert(uintptr_t(prev) != kMallocFreeWord);
-  next->prev = prev;
-  prev->next = next;
-}
-
-void StringData::sweepAll() {
-  SweepNode& head = MemoryManager::TheMemoryManager()->m_strings;
-  for (SweepNode *next, *n = head.next; n != &head; n = next) {
-    next = n->next;
-    assert(next && uintptr_t(next) != kSmartFreeWord);
-    assert(next && uintptr_t(next) != kMallocFreeWord);
-    StringData* s = (StringData*)(uintptr_t(n) -
-                                  offsetof(StringData, m_big.node));
-    assert(s->isShared());
-    s->m_big.shared->decRef();
-  }
-  head.next = head.prev = &head;
-}
-
 HOT_FUNC
 void StringData::initAttach(const char* data) {
   return initAttach(data, strlen(data));
@@ -335,13 +300,11 @@ HOT_FUNC
 StringData::StringData(SharedVariant *shared)
   : _count(0) {
   assert(shared && size_t(shared->stringLength()) <= size_t(MaxSize));
-  shared->incRef();
   m_hash = 0;
   m_len = shared->stringLength();
   m_cdata = shared->stringData();
   m_big.shared = shared;
   m_big.cap = m_len | IsShared;
-  enlist();
 }
 
 HOT_FUNC
@@ -353,8 +316,6 @@ void StringData::releaseData() {
     break;
   case IsShared:
     assert(checkSane());
-    m_big.shared->decRef();
-    delist();
     break;
   case IsSmart:
     assert(checkSane());
@@ -434,10 +395,6 @@ void StringData::append(const char *s, int len) {
     // buffer is immutable, don't modify it.
     StringSlice r = slice();
     char* newdata = smart_concat(r.ptr, r.len, s, len);
-    if (isShared()) {
-      m_big.shared->decRef();
-      delist();
-    }
     m_len = newlen;
     m_data = newdata;
     m_big.cap = newlen | IsSmart;
diff --git a/hphp/runtime/base/string_data.h b/hphp/runtime/base/string_data.h
index 388c88eac..87eb8514f 100644
--- a/hphp/runtime/base/string_data.h
+++ b/hphp/runtime/base/string_data.h
@@ -128,14 +128,6 @@ class StringData {
   void setStatic() const;
   bool isStatic() const { return _count == RefCountStaticValue; }
 
-  /**
-   * Get the wrapped SharedVariant.
-   */
-  SharedVariant *getSharedVariant() const {
-    if (isShared()) return m_big.shared;
-    return nullptr;
-  }
-
   static StringData *Escalate(StringData *in);
 
   /**
@@ -344,7 +336,6 @@ public:
   DECLARE_SMART_ALLOCATION(StringData);
   void dump() const;
   std::string toCPPString() const;
-  static void sweepAll();
 
   static StringData *FindStaticString(const StringData* str);
   static StringData *GetStaticString(const StringData* str);
@@ -385,9 +376,8 @@ public:
       // Calculate padding so that node, shared, and cap are pointer aligned,
       // and ensure cap overlaps the last byte of m_small.
       static const size_t kPadding = sizeof(m_small) -
-        sizeof(SweepNode) - sizeof(SharedVariant*) - sizeof(uint64_t);
+        sizeof(SharedVariant*) - sizeof(uint64_t);
       char junk[kPadding];
-      SweepNode node;
       SharedVariant *shared;
       uint64_t cap;
     } m_big;
@@ -408,8 +398,6 @@ public:
   void releaseData();
   int numericCompare(const StringData *v2) const;
   MutableSlice escalate(uint32_t cap); // change to smart-malloced string
-  void enlist();
-  void delist();
 
   strhash_t hashHelper() const NEVER_INLINE;
 
diff --git a/hphp/runtime/base/type_variant.cpp b/hphp/runtime/base/type_variant.cpp
index 415f8b3ae..fc267c31b 100644
--- a/hphp/runtime/base/type_variant.cpp
+++ b/hphp/runtime/base/type_variant.cpp
@@ -3187,19 +3187,6 @@ Variant Variant::share(bool save) const {
   return false; // same as non-existent
 }
 
-SharedVariant *Variant::getSharedVariant() const {
-  if (m_type == KindOfRef) {
-    return m_data.pref->var()->getSharedVariant();
-  }
-  if (m_type == KindOfString) {
-    return m_data.pstr->getSharedVariant();
-  }
-  if (m_type == KindOfArray) {
-    return m_data.parr->getSharedVariant();
-  }
-  return nullptr;
-}
-
 void Variant::dump() const {
   VariableSerializer vs(VariableSerializer::VarDump);
   String ret(vs.serialize(*this, true));
diff --git a/hphp/runtime/base/type_variant.h b/hphp/runtime/base/type_variant.h
index 9058517ac..ba52ed253 100644
--- a/hphp/runtime/base/type_variant.h
+++ b/hphp/runtime/base/type_variant.h
@@ -776,11 +776,6 @@ class Variant : private TypedValue {
    */
   Variant share(bool save) const;
 
-  /**
-   * Get the wrapped SharedVariant, if any.
-   */
-  SharedVariant *getSharedVariant() const;
-
   /**
    * Memory allocator methods.
    */
diff --git a/hphp/runtime/vm/bytecode.cpp b/hphp/runtime/vm/bytecode.cpp
index e49ce1358..a3e9ecbc8 100644
--- a/hphp/runtime/vm/bytecode.cpp
+++ b/hphp/runtime/vm/bytecode.cpp
@@ -31,7 +31,9 @@
 #include "hphp/util/trace.h"
 #include "hphp/util/debug.h"
 #include "hphp/runtime/base/stat_cache.h"
+#include "hphp/runtime/base/shared/shared_variant.h"
 
+#include "hphp/runtime/vm/treadmill.h"
 #include "hphp/runtime/vm/php_debug.h"
 #include "hphp/runtime/vm/debugger_hook.h"
 #include "hphp/runtime/vm/runtime.h"
@@ -2897,6 +2899,25 @@ VMExecutionContext::pushLocalsAndIterators(const Func* func,
   }
 }
 
+void VMExecutionContext::enqueueSharedVar(SharedVariant* svar) {
+  m_freedSvars.push_back(svar);
+}
+
+class FreedSVars : public Treadmill::WorkItem {
+  SVarVector m_svars;
+public:
+  explicit FreedSVars(SVarVector&& svars) : m_svars(std::move(svars)) {}
+  virtual void operator()() {
+    for (auto it = m_svars.begin(); it != m_svars.end(); it++) {
+      delete *it;
+    }
+  }
+};
+
+void VMExecutionContext::treadmillSharedVars() {
+  Treadmill::WorkItem::enqueue(new FreedSVars(std::move(m_freedSvars)));
+}
+
 void VMExecutionContext::destructObjects() {
   if (UNLIKELY(RuntimeOption::EnableObjDestructCall)) {
     while (!m_liveBCObjs.empty()) {
@@ -7577,6 +7598,7 @@ void VMExecutionContext::requestInit() {
 }
 
 void VMExecutionContext::requestExit() {
+  treadmillSharedVars();
   destructObjects();
   syncGdbState();
   tx64->requestExit();