Virtualizing Mutually Exclusive Locks for Immutable Shared Objects
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Solution Overview
Problem
Transparent sharing of immutable objects across tasks in multi-threaded programming environments leads to potential inter-task interference due to monitor activity, which can result in performance issues and security vulnerabilities like denial-of-service attacks, making it difficult to allow sharing while preventing lock-related interferences.
Innovation Solution
The method dynamically virtualizes the monitor of an object into a set of monitors when multiple tasks execute monitor operations simultaneously, allowing threads from different tasks to fast lock and unlock immutable shared objects, and inflating or virtualizing locks as needed to prevent interference, with virtualization only occurring in the slow path of monitor acquisition, thus minimizing overhead in frequent cases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If immutable objects are shared transparently across multiple tasks, then memory footprint is reduced, but inter-task interference occurs through monitor activity
Solution Approach 1:
The patent segments the shared immutable object into task-specific copies when interference is detected. Each task receives its own copy of the object, eliminating monitor contention while maintaining the appearance of shared access. This resolves the contradiction by allowing memory sharing when safe and creating separate copies only when needed to prevent interference.
Solution Approach 2:
The patent introduces a monitor virtualization mechanism as an intermediary layer between tasks and shared objects. This virtualizer intercepts monitor operations and dynamically determines whether to grant access or create copies, mediating between the desire for shared memory and the need to prevent interference.
2Reliability
If monitor virtualization is applied to all lock acquisitions, then inter-task interference is prevented, but performance overhead increases
Solution Approach 1:
The patent applies monitor virtualization selectively rather than universally. It performs partial virtualization by checking for task identity in the slow path of lock acquisition only when necessary, rather than applying full virtualization to all lock operations. This maintains high performance for uncontended locks while preventing interference when needed.
Solution Approach 2:
The patent applies different levels of monitoring to different situations. Fast path lock acquisitions (same task) receive minimal oversight, while slow path acquisitions (potential cross-task) receive full virtualization checking. This local differentiation optimizes performance while maintaining reliability.
3Reliability
If copy-on-first-lock-acquisition is used to prevent interference, then monitor contention is eliminated, but updating all references becomes extremely costly
Solution Approach 1:
Instead of copying the entire object graph, the patent segments the solution to only copy the specific immutable object that caused the interference. This limited segmentation avoids the exponential complexity of updating all references while still eliminating the specific monitor contention problem.
Solution Approach 2:
The patent uses selective copying of only the necessary immutable object rather than comprehensive copying of all references. This targeted copying approach achieves interference prevention with minimal overhead by copying only when and where needed.
Data Source
AI summary
A method is provided to virtualize a mutually exclusive lock of a shared immutable object. A determination is made whether any threads have locked the immutable shared object. If threads have not locked the immutable shared object, threads of different tasks are allowed to fast lock and unlock the immutable shared object. If a thread requests the lock of an immutable shared object and the object is fast locked by another thread when both threads are from an equivalent task, the lock of the immutable shared object is inflated and the requesting thread is blocked. If a thread requests the lock of an immutable shared object and the object is fast locked by another thread when both threads are from different tasks, the lock of the immutable shared object is virtualized and granted to the requesting thread.