diff options
| -rw-r--r-- | indra/llcommon/llhandle.h | 58 |
1 files changed, 47 insertions, 11 deletions
diff --git a/indra/llcommon/llhandle.h b/indra/llcommon/llhandle.h index 37c657dd92..6af5e198d6 100644 --- a/indra/llcommon/llhandle.h +++ b/indra/llcommon/llhandle.h @@ -31,6 +31,10 @@ #include <boost/type_traits/is_convertible.hpp> #include <boost/utility/enable_if.hpp> +/** + * Helper object for LLHandle. Don't instantiate these directly, used + * exclusively by LLHandle. + */ class LLTombStone : public LLRefCount { public: @@ -42,15 +46,37 @@ private: mutable void* mTarget; }; -// LLHandles are used to refer to objects whose lifetime you do not control or influence. -// Calling get() on a handle will return a pointer to the referenced object or NULL, -// if the object no longer exists. Note that during the lifetime of the returned pointer, -// you are assuming that the object will not be deleted by any action you perform, -// or any other thread, as normal when using pointers, so avoid using that pointer outside of -// the local code block. -// -// https://wiki.lindenlab.com/mediawiki/index.php?title=LLHandle&oldid=79669 - +/** + * LLHandles are used to refer to objects whose lifetime you do not control or influence. + * Calling get() on a handle will return a pointer to the referenced object or NULL, + * if the object no longer exists. Note that during the lifetime of the returned pointer, + * you are assuming that the object will not be deleted by any action you perform, + * or any other thread, as normal when using pointers, so avoid using that pointer outside of + * the local code block. + * + * https://wiki.lindenlab.com/mediawiki/index.php?title=LLHandle&oldid=79669 + * + * The implementation is like some "weak pointer" implementations. When we + * can't control the lifespan of the referenced object of interest, we can + * still instantiate a proxy object whose lifespan we DO control, and store in + * the proxy object a dumb pointer to the actual target. Then we just have to + * ensure that on destruction of the target object, the proxy's dumb pointer + * is set NULL. + * + * LLTombStone is our proxy object. LLHandle contains an LLPointer to the + * LLTombStone, so every copy of an LLHandle increments the LLTombStone's ref + * count as usual. + * + * One copy of the LLHandle, specifically the LLRootHandle, must be stored in + * the referenced object. Destroying the LLRootHandle is what NULLs the + * proxy's target pointer. + * + * Minor optimization: we want LLHandle's mTombStone to always be a valid + * LLPointer, saving some conditionals in dereferencing. That's the + * getDefaultTombStone() mechanism. The default LLTombStone object's target + * pointer is always NULL, so it's semantically identical to allowing + * mTombStone to be invalid. + */ template <typename T> class LLHandle { @@ -108,6 +134,14 @@ private: } }; +/** + * LLRootHandle isa LLHandle which must be stored in the referenced object. + * You can either store it directly and explicitly bind(this), or derive from + * LLHandleProvider (q.v.) which automates that for you. The essential point + * is that destroying the LLRootHandle (as a consequence of destroying the + * referenced object) calls unbind(), setting the LLTombStone's target pointer + * NULL. + */ template <typename T> class LLRootHandle : public LLHandle<T> { @@ -144,8 +178,10 @@ private: LLRootHandle(const LLRootHandle& other) {}; }; -// Use this as a mixin for simple classes that need handles and when you don't -// want handles at multiple points of the inheritance hierarchy +/** + * Use this as a mixin for simple classes that need handles and when you don't + * want handles at multiple points of the inheritance hierarchy + */ template <typename T> class LLHandleProvider { |