dom/base/nsDOMScriptObjectHolder.h

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  22  * Contributor(s):
  23  *      Mark Hammond <mhammond@skippinet.com.au>
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  38
  39 #ifndef nsDOMScriptObjectHolder_h__
  40 #define nsDOMScriptObjectHolder_h__
  41
  42 #include "nsIScriptContext.h"
  43 #include "nsIDOMScriptObjectFactory.h"
  44
  45 // A thin class used to help with script object memory management.  No virtual
  46 // functions and a fully inline implementation should keep the cost down.
  47 // [Note that a fully inline implementation is necessary for use by other
  48 // languages, which do not link against the layout component module]
  49 class NS_STACK_CLASS nsScriptObjectHolder {
  50 public:
  51   // A constructor that will cause a reference to |ctx| to be stored in
  52   // the object.  Only use for short-lived object holders.
  53   nsScriptObjectHolder(nsIScriptContext *ctx, void *aObject = nsnull) :
  54       mObject(aObject), mContext(ctx) {
  55     NS_ASSERTION(ctx, "Must provide a valid context");
  56   }
  57
  58   // copy constructor
  59   nsScriptObjectHolder(const nsScriptObjectHolder& other) :
  60       mObject(other.mObject),
  61       mContext(other.mContext)
  62   {
  63     // New hold the script object and new reference on the script context.
  64     if (mObject)
  65       mContext->HoldScriptObject(mObject);
  66   }
  67
  68   ~nsScriptObjectHolder() {
  69     if (mObject)
  70       mContext->DropScriptObject(mObject);
  71   }
  72
  73   // misc operators
  74   nsScriptObjectHolder &operator=(const nsScriptObjectHolder &other) {
  75     set(other);
  76     return *this;
  77   }
  78   PRBool operator!() const {
  79     return !mObject;
  80   }
  81   operator void *() const {
  82     return mObject;
  83   }
  84
  85   // Drop the script object - but *not* the nsIScriptContext.
  86   nsresult drop() {
  87     nsresult rv = NS_OK;
  88     if (mObject) {
  89       rv = mContext->DropScriptObject(mObject);
  90       mObject = nsnull;
  91     }
  92     return rv;
  93   }
  94   nsresult set(void *object) {
  95     NS_ASSERTION(getScriptTypeID() != nsIProgrammingLanguage::UNKNOWN,
  96                  "Must know the language!");
  97     nsresult rv = drop();
  98     if (NS_FAILED(rv))
  99       return rv;
 100     if (object) {
 101       rv = mContext->HoldScriptObject(object);
 102       // don't store the pointer if we failed to lock it.
 103       if (NS_SUCCEEDED(rv)) {
 104         mObject = object;
 105       }
 106     }
 107     return rv;
 108   }
 109   nsresult set(const nsScriptObjectHolder &other) {
 110     NS_ASSERTION(getScriptTypeID() == other.getScriptTypeID(),
 111                  "Must have identical languages!");
 112     nsresult rv = drop();
 113     if (NS_FAILED(rv))
 114       return rv;
 115     return set(other.mObject);
 116   }
 117   // Get the language ID.
 118   PRUint32 getScriptTypeID() const {
 119     return mContext->GetScriptTypeID();
 120   }
 121 protected:
 122   void *mObject;
 123   nsCOMPtr<nsIScriptContext> mContext;
 124 };
 125
 126 #endif // nsDOMScriptObjectHolder_h__