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CSE522-Assignment 4 Part 1 Concurrent Mutator-Collector Simulator Solved
Java uses a variety of garbage-collection techniques, one of which is the Concurrent Mark Sweep (CMS) Collector. Lecture 17 describes the two main problems of concurrent marking. In this part of the assignment you are to program a solution to these problems for the specific example where the mutator performs sequential insert and delete operations on a binary search tree (BST).
Posted on Piazza:Resources à Assignments is a file ConcurrentMarking.java consisting of two thread classes, Mutator and Collector, and a main method which creates and starts these two threads concurrently. The class Mutator inserts a sequence of values into a BST and then deletes some of the values from the BST. The Collector class defines the mark method which performs a depth-first traversal of the BST and sets the mark_bit fields of all nodes to true. The definitions of the BST class Tree and the insert and delete methods are as in Assignment 1 and are given in the posted file.
(i) the mark_bit fields of some of the un-deleted nodes of the tree are false; and (ii) the mark_bit fields of some deleted nodes are true. The cause of both problems is that the collector visited these nodes before some of their fields got modified. Solve the first problem by extending Tree.insert so that the mark_bit fields for these nodes are set to true, and add the node values to the sorted list, re_mark_true, in class Collector. Solve the second problem by extending Tree.case1 and Tree.case2 so that the mark_bit fields for these nodes are set to false, and add the node values to the sorted list, re_mark_true, in class Collector.
What to Code. The amount of your coding is very small and it is very systematic. In practice, the compiler emits a small amount of code before every write operation to a variable that could hold an object reference. This code would alert the garbage collector as to where re-marking is necessary. Your Java code extensions should effectively carry out the required re-marking. The lists re_mark_true and re_mark_false help us see what re-markings took place.
After making the required extensions, run your revised ConcurrentMarking.java under JIVE and proceed as follows:
1. Save the object diagram (stacked with tables) in a file called A4_obj.png.
2. Check the JIVE object diagram to make sure that the mark_bit values are correct for the (undeleted) nodes of the tree as well as for the deleted nodes of the tree.
3. For the given test case, the values 50, 90, 100 and 150 involve a case3 delete, hence the nodes containing these values are replaced, respectively, by values 55, 95, 133, and 160. Thus, the values 55, 95, 133, and 160 should appear in the list of deleted nodes at the bottom of the object diagram (rather than 50, 90, 100, and 150).
4. Perform a JIVE Search with mark_bit == false, and check that all the objects in the Search Results are present among deleted objects at the bottom of the Object Diagram and also that the values in the objects appear on the Console under ‘Nodes deleted late’. For any additional deleted Tree objects in the Object Diagram, perform a JIVE Search for their mark_bit and check that are 0 assignments to the mark_bit.
Posted on Piazza:Resources à Assignments is a file ConcurrentMarking.java consisting of two thread classes, Mutator and Collector, and a main method which creates and starts these two threads concurrently. The class Mutator inserts a sequence of values into a BST and then deletes some of the values from the BST. The Collector class defines the mark method which performs a depth-first traversal of the BST and sets the mark_bit fields of all nodes to true. The definitions of the BST class Tree and the insert and delete methods are as in Assignment 1 and are given in the posted file.
(i) the mark_bit fields of some of the un-deleted nodes of the tree are false; and (ii) the mark_bit fields of some deleted nodes are true. The cause of both problems is that the collector visited these nodes before some of their fields got modified. Solve the first problem by extending Tree.insert so that the mark_bit fields for these nodes are set to true, and add the node values to the sorted list, re_mark_true, in class Collector. Solve the second problem by extending Tree.case1 and Tree.case2 so that the mark_bit fields for these nodes are set to false, and add the node values to the sorted list, re_mark_true, in class Collector.
What to Code. The amount of your coding is very small and it is very systematic. In practice, the compiler emits a small amount of code before every write operation to a variable that could hold an object reference. This code would alert the garbage collector as to where re-marking is necessary. Your Java code extensions should effectively carry out the required re-marking. The lists re_mark_true and re_mark_false help us see what re-markings took place.
After making the required extensions, run your revised ConcurrentMarking.java under JIVE and proceed as follows:
1. Save the object diagram (stacked with tables) in a file called A4_obj.png.
2. Check the JIVE object diagram to make sure that the mark_bit values are correct for the (undeleted) nodes of the tree as well as for the deleted nodes of the tree.
3. For the given test case, the values 50, 90, 100 and 150 involve a case3 delete, hence the nodes containing these values are replaced, respectively, by values 55, 95, 133, and 160. Thus, the values 55, 95, 133, and 160 should appear in the list of deleted nodes at the bottom of the object diagram (rather than 50, 90, 100, and 150).
4. Perform a JIVE Search with mark_bit == false, and check that all the objects in the Search Results are present among deleted objects at the bottom of the Object Diagram and also that the values in the objects appear on the Console under ‘Nodes deleted late’. For any additional deleted Tree objects in the Object Diagram, perform a JIVE Search for their mark_bit and check that are 0 assignments to the mark_bit.
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