Improve resiliency of entities when destroyed #897
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entity.js - added _destroy(), isDestroyed() - added cache to hold obsolete _handles to avoid premature GC entity.d.ts - added isDestroyed() node.js - added guard statements to execute() to filter out destroyed entities action/client.js - added _destory() and isDestroyed() - refactored destroy() flow action/server.js - added _destory() and isDestroyed() - refactored destroy() flows main.ts - added tests for isDestroyed() to entity subclasses test-destruction.js - added entity.destory() test cases
minggangw
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Feb 27, 2023
entity.js - added static gcHandles() node.js - revised execute() to use for-of loops for each entity type. This simplifies the looping of each group of entities through the use of loop interruption (e.g., use continue statement) to detect a destroyed entity before processing. Additionally it the for-of loop reduces the number of isDestroyed() calls Lastly, added a call to Entity.gcHandles() prior to exiting the method.
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@minggangw my latest commit 9af468f to address your suggestion may have overwritten f3840e2 |
minggangw
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Sorry for missing this comment, the change looks good to me, thanks! |
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LGTM! Thanks for fixing the crashing issue
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Hi @wayneparrott I have approved this PR, please go ahead to merge it after resolving the conflict, thanks! |
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* improve entity destroy() resiliency #896 entity.js - added _destroy(), isDestroyed() - added cache to hold obsolete _handles to avoid premature GC entity.d.ts - added isDestroyed() node.js - added guard statements to execute() to filter out destroyed entities action/client.js - added _destory() and isDestroyed() - refactored destroy() flow action/server.js - added _destory() and isDestroyed() - refactored destroy() flows main.ts - added tests for isDestroyed() to entity subclasses test-destruction.js - added entity.destory() test cases * improve destroyed entity handling to avoid segfault entity.js - added static gcHandles() node.js - revised execute() to use for-of loops for each entity type. This simplifies the looping of each group of entities through the use of loop interruption (e.g., use continue statement) to detect a destroyed entity before processing. Additionally it the for-of loop reduces the number of isDestroyed() calls Lastly, added a call to Entity.gcHandles() prior to exiting the method.
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Issue #896 identifies an race condition where multiple subscriptions listen to a common topic and one subscription, from it's callback destroys another subscription (an entity). This revealed an issue where i/o activity can exists on an entity's _handle after the entity has been destroyed. The result is an invalid entity pointer or worse a SEGFAULT. To address this I've added destroy state semantics to the Entity class.
full disclosure:
One quirky behavior I've attempted to resolve is that setting
Entity._handle = null, results in the _handle being quickly GC'ed. This causes the SEGFAULT when the handle is still referenced by ShadowNode.Execute(). I believe after calling _handle.release(), the handle must not be GC'ed until after the current Node.execute() completes. I was not sure how to pull this off in C with Nan API so I implemented a hack by using a cache to hold_handle's after theirrelease(). The cache will flush when its size exceeds a const (100 atm). I'm definitely open to revising this hack with the suggestion of others.entity.js
entity.d.ts
node.js
action/client.js
action/server.js
main.ts
test-destruction.js
Fix #896