Garbage collection basics in Compiler Design - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to identify unreachable objects in a heap.

Compiler Design

unreachable_objects = [obj for obj in heap if obj not in [1]]

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Avariables

Bstack

Cheap

Droots

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing heap with roots

Using stack instead of roots

The roots set contains all objects directly accessible by the program. Objects not reachable from roots are considered unreachable.

2fill in blank

medium

Complete the code to mark reachable objects during garbage collection.

Compiler Design

def mark(obj):
    if obj not in marked:
        marked.add(obj)
        for ref in obj.[1]:
            mark(ref)

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Areferences

Bchildren

Cpointers

Dlinks

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'children' which is not a standard term

Using 'links' which is ambiguous

Each object has references to other objects. We recursively mark all referenced objects as reachable.

3fill in blank

hard

Fix the error in the code to sweep unmarked objects from the heap.

Compiler Design

for obj in heap[:]:
    if obj not in [1]:
        heap.remove(obj)

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Astack

Broots

Cmarked

Dvisited

Attempts:

3 left

💡 Hint

Common Mistakes

Removing objects not in roots (too broad)

Using stack which is unrelated here

Only objects not marked as reachable should be removed from the heap during the sweep phase.

4fill in blank

hard

Fill both blanks to implement reference counting update after object assignment.

Compiler Design

def assign(obj, new_ref):
    obj.ref_count [1] 1
    new_ref.ref_count [2] 1

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A-=

B+=

C*=

D/=

Attempts:

3 left

💡 Hint

Common Mistakes

Increasing old ref count

Decreasing new ref count

When an object reference is replaced, the old object's reference count decreases and the new object's reference count increases.

5fill in blank

hard

Fill both blanks to create a dictionary comprehension that maps objects to their reference counts if count is greater than zero.

Compiler Design

ref_counts = {obj[1]: obj.ref_count : obj.ref_count for obj in heap if obj.ref_count [2] 0}

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A.id

B:

C>

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' instead of '>' in condition

Using ':' incorrectly in comprehension

The dictionary maps object IDs to their reference counts, but only includes objects with positive reference counts.