diff options
Diffstat (limited to 'indra/llcommon/llsd.h')
| -rw-r--r-- | indra/llcommon/llsd.h | 82 |
1 files changed, 80 insertions, 2 deletions
diff --git a/indra/llcommon/llsd.h b/indra/llcommon/llsd.h index 90d0f97873..1ffa1d279b 100644 --- a/indra/llcommon/llsd.h +++ b/indra/llcommon/llsd.h @@ -80,9 +80,73 @@ An array is a sequence of zero or more LLSD values. + Thread Safety + + In general, these LLSD classes offer *less* safety than STL container + classes. Implementations prior to this one were unsafe even when + completely unrelated LLSD trees were in two threads due to reference + sharing of special 'undefined' values that participated in the reference + counting mechanism. + + The dereference-before-refcount and aggressive tree sharing also make + it impractical to share an LLSD across threads. A strategy of passing + ownership or a copy to another thread is still difficult due to a lack + of a cloning interface but it can be done with some care. + + One way of transferring ownership is as follows: + + void method(const LLSD input) { + ... + LLSD * xfer_tree = new LLSD(); + { + // Top-level values + (* xfer_tree)['label'] = "Some text"; + (* xfer_tree)['mode'] = APP_MODE_CONSTANT; + + // There will be a second-level + LLSD subtree(LLSD::emptyMap()); + (* xfer_tree)['subtree'] = subtree; + + // Do *not* copy from LLSD objects via LLSD + // intermediaries. Only use plain-old-data + // types as intermediaries to prevent reference + // sharing. + subtree['value1'] = input['value1'].asInteger(); + subtree['value2'] = input['value2'].asString(); + + // Close scope and drop 'subtree's reference. + // Only xfer_tree has a reference to the second + // level data. + } + ... + // Transfer the LLSD pointer to another thread. Ownership + // transfers, this thread no longer has a reference to any + // part of the xfer_tree and there's nothing to free or + // release here. Receiving thread does need to delete the + // pointer when it is done with the LLSD. Transfer + // mechanism must perform correct data ordering operations + // as dictated by architecture. + other_thread.sendMessageAndPointer("Take This", xfer_tree); + xfer_tree = NULL; + + + Avoid this pattern which provides half of a race condition: + + void method(const LLSD input) { + ... + LLSD xfer_tree(LLSD::emptyMap()); + xfer_tree['label'] = "Some text"; + xfer_tree['mode'] = APP_MODE_CONSTANT; + ... + other_thread.sendMessageAndPointer("Take This", xfer_tree); + + @nosubgrouping */ +// Normally undefined, used for diagnostics +//#define LLSD_DEBUG_INFO 1 + class LL_COMMON_API LLSD { public: @@ -266,7 +330,7 @@ public: /** @name Type Testing */ //@{ enum Type { - TypeUndefined, + TypeUndefined = 0, TypeBoolean, TypeInteger, TypeReal, @@ -276,7 +340,10 @@ public: TypeURI, TypeBinary, TypeMap, - TypeArray + TypeArray, + TypeLLSDTypeEnd, + TypeLLSDTypeBegin = TypeUndefined, + TypeLLSDNumTypes = (TypeLLSDTypeEnd - TypeLLSDTypeBegin) }; Type type() const; @@ -338,6 +405,17 @@ private: /// Returns Notation version of llsd -- only to be called from debugger static const char *dump(const LLSD &llsd); //@} + +public: + void dumpStats() const; // Output information on object and usage + void calcStats(S32 type_counts[], S32 share_counts[]) const; // Calculate the number of LLSD objects used by this value + + static std::string typeString(Type type); // Return human-readable type as a string + +#ifdef LLSD_DEBUG_INFO + static S32 sLLSDAllocationCount; // Number of LLSD objects ever created + static S32 sLLSDNetObjects; // Number of LLSD objects that exist +#endif }; struct llsd_select_bool : public std::unary_function<LLSD, LLSD::Boolean> |