Improve ref counting.

Passing arrays back and forth between PHP and JavaScript means we need
to get a handle on pass-by-value and references.  Unfortunately we can't
get compile-time-pass-by-reference to work with magic methods, so tweak
so that we always separate the zvals we get to ensure they are
pass-by-value (and don't corrupt copy-on-write aliases).  We'll need to
use an explicit wrapper class to pass arrays by reference to JS.

Author: cscott

src/asyncmapperchannel.cc

@@ -113,14 +113,19 @@ objid_t AsyncMapperChannel::IdForPhpObj(zval *z) {
 
   objid_t id = NewId();
   if (id >= php_obj_list_.size()) { php_obj_list_.resize(id + 1); }
-  // XXX Should we clone/separate z?
+  // Pass by value.  Note that we seem to be very rarely (never?)
+  // given refs.
   Z_ADDREF_P(z);
-  php_obj_list_[id] = z;
   if (Z_TYPE_P(z) == IS_OBJECT) {
     php_obj_to_id_[handle] = id;
   } else {
+    // We're going to modify this from JS side, so make sure we have
+    // a unique copy (otherwise other copy-on-write references on the
+    // PHP side could be unexpectedly altered).
+    z = ZVal::Separate(z);
     php_arr_to_id_[z] = id;
   }
+  php_obj_list_[id] = z;
   return id;
 }
 

src/values.h

@@ -90,6 +90,17 @@ class ZVal {
   inline zval ** PtrPtr() { return &zvalp; }
   inline zval * Escape() { Z_ADDREF_P(zvalp); return zvalp; }
 
+  // Ensure an unshared copy of this value.
+  inline void Separate() {
+    assert(!transferred_);
+    SEPARATE_ZVAL_IF_NOT_REF(&zvalp);
+  }
+  // A static version that will work on unwrapped zval*
+  static inline zval *Separate(zval *z) {
+    SEPARATE_ZVAL_IF_NOT_REF(&z);
+    return z;
+  }
+
   // Support a PHP calling convention where the actual zval object
   // is owned by the caller, but the contents are transferred to the
   // callee.