From 9d5b897600a8f9405ec37a141b9417f34a11c557 Mon Sep 17 00:00:00 2001 From: Nat Goodspeed Date: Mon, 2 Dec 2019 14:39:24 -0500 Subject: DRTVWR-494: Defend LLInstanceTracker against multi-thread usage. The previous implementation went to some effort to crash if anyone attempted to create or destroy an LLInstanceTracker subclass instance during traversal. That restriction is manageable within a single thread, but becomes unworkable if it's possible that a given subclass might be used on more than one thread. Remove LLInstanceTracker::instance_iter, beginInstances(), endInstances(), also key_iter, beginKeys() and endKeys(). Instead, introduce key_snapshot() and instance_snapshot(), the only means of iterating over LLInstanceTracker instances. (These are intended to resemble functions, but in fact the current implementation simply presents the classes.) Iterating over a captured snapshot defends against container modifications during traversal. The term 'snapshot' reminds the coder that a new instance created during traversal will not be considered. To defend against instance deletion during traversal, a snapshot stores std::weak_ptrs which it lazily dereferences, skipping on the fly any that have expired. Dereferencing instance_snapshot::iterator gets you a reference rather than a pointer. Because some use cases want to delete all existing instances, add an instance_snapshot::deleteAll() method that extracts the pointer. Those cases used to require explicitly copying instance pointers into a separate container; instance_snapshot() now takes care of that. It remains the caller's responsibility to ensure that all instances of that LLInstanceTracker subclass were allocated on the heap. Replace unkeyed static LLInstanceTracker::getInstance(T*) -- which returned nullptr if that instance had been destroyed -- with new getWeak() method returning std::weak_ptr. Caller must detect expiration of that weak_ptr. Adjust tests accordingly. Use of std::weak_ptr to detect expired instances requires engaging std::shared_ptr in the constructor. We now store shared_ptrs in the static containers (std::map for keyed, std::set for unkeyed). Make LLInstanceTrackerBase a template parameterized on the type of the static data it manages. For that reason, hoist static data class declarations out of the class definitions to an LLInstanceTrackerStuff namespace. Remove the static atomic sIterationNestDepth and its methods incrementDepth(), decrementDepth() and getDepth(), since they were used only to forbid creation and destruction during traversal. Add a std::mutex to static data. Introduce an internal LockStatic class that locks the mutex while providing a pointer to static data, making that the only way to access the static data. The LLINSTANCETRACKER_DTOR_NOEXCEPT macro goes away because we no longer expect ~LLInstanceTracker() to throw an exception in test programs. That affects LLTrace::StatBase as well as LLInstanceTracker itself. Adapt consumers to the new LLInstanceTracker API. --- indra/llxml/llcontrol.h | 2 -- 1 file changed, 2 deletions(-) (limited to 'indra/llxml') diff --git a/indra/llxml/llcontrol.h b/indra/llxml/llcontrol.h index de0d366492..39e1d3e615 100644 --- a/indra/llxml/llcontrol.h +++ b/indra/llxml/llcontrol.h @@ -200,8 +200,6 @@ public: LLControlGroup(const std::string& name); ~LLControlGroup(); void cleanup(); - - typedef LLInstanceTracker::instance_iter instance_iter; LLControlVariablePtr getControl(const std::string& name); -- cgit v1.2.3