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Make unsafe borrow checking O(1) via active-borrow tracking #97

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Merged
DanexCodr merged 2 commits into from
Apr 13, 2026
Merged

Make unsafe borrow checking O(1) via active-borrow tracking #97

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68d34c3
Add O(1) active borrow tracking
Copilot Apr 13, 2026
64d5473
Finalize zero-cost borrow checker tracking
Copilot Apr 13, 2026
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2 changes: 1 addition & 1 deletion src/main/java/cod/interpreter/InterpreterVisitor.java
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Original file line number Diff line number Diff line change
Expand Up @@ -240,7 +240,7 @@ public Object visit(Field n) {
throw new ProgramError("Cannot redeclare field: " + n.name);
}
}
ctx.objectInstance.fields.put(n.name, val);
ctx.setObjectField(n.name, val);
return val;
}

Expand Down
119 changes: 113 additions & 6 deletions src/main/java/cod/interpreter/context/ExecutionContext.java
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Expand Up @@ -44,6 +44,7 @@ protected Integer initialValue() {
private boolean inOptimizedLoop = false;
private List<Object> pendingOutputs = new ArrayList<Object>();
private boolean unsafeExecutionContext = false;
private IdentityHashMap<Object, Map<Long, Integer>> activeBorrowsByContainer;

// ========== TYPE HANDLER ==========
private final TypeHandler typeHandler;
Expand Down Expand Up @@ -155,6 +156,7 @@ public ExecutionContext(ObjectInstance obj, Map<String, Object> locals,
this.currentMethodName = null;
this.currentLambdaClosure = null;
this.typeHandler = typeHandler;
this.activeBorrowsByContainer = new IdentityHashMap<Object, Map<Long, Integer>>();

// Initialize locals
this.localsStack = new ArrayList<Map<String, Object>>();
Expand All @@ -176,6 +178,7 @@ public ExecutionContext(ObjectInstance obj, Map<String, Object> locals,

// Build optimized slot access structures
optimizeSlotAccess();
registerInitialBorrowState(initialLocals);
}

/**
Expand Down Expand Up @@ -236,7 +239,8 @@ public void setSlotValue(String slotName, Object value) {
}

// Update both representations
slotValues.put(slotName, value);
Object previous = slotValues.put(slotName, value);
replaceTrackedValue(previous, value);

if (slotsOptimized && slotIndexMap.containsKey(slotName)) {
int index = slotIndexMap.get(slotName);
Expand Down Expand Up @@ -326,7 +330,10 @@ public void pushScope() {

public void popScope() {
if (localsStack.size() > 1) {
localsStack.remove(localsStack.size() - 1);
Map<String, Object> removedScope = localsStack.remove(localsStack.size() - 1);
for (Object value : removedScope.values()) {
unregisterBorrowsFromValue(value);
}
localTypesStack.remove(localTypesStack.size() - 1);
}
}
Expand Down Expand Up @@ -373,14 +380,16 @@ public void setVariable(String name, Object value) {
for (int i = localsStack.size() - 1; i >= 0; i--) {
Map<String, Object> scope = localsStack.get(i);
if (scope.containsKey(name)) {
scope.put(name, value);
Object previous = scope.put(name, value);
replaceTrackedValue(previous, value);
return;
}
}

// Create in current scope
Map<String, Object> currentScope = localsStack.get(localsStack.size() - 1);
currentScope.put(name, value);
Object previous = currentScope.put(name, value);
replaceTrackedValue(previous, value);
}

public String getVariableType(String name) {
Expand Down Expand Up @@ -423,7 +432,9 @@ public Object removeVariable(String name) {
for (int i = localsStack.size() - 1; i >= 0; i--) {
Map<String, Object> scope = localsStack.get(i);
if (scope.containsKey(name)) {
return scope.remove(name);
Object removed = scope.remove(name);
unregisterBorrowsFromValue(removed);
return removed;
}
}
return null;
Expand All @@ -440,7 +451,8 @@ public boolean removeVariableFromAllScopes(String name) {
for (int i = localsStack.size() - 1; i >= 0; i--) {
Map<String, Object> scope = localsStack.get(i);
if (scope.containsKey(name)) {
scope.remove(name);
Object removed = scope.remove(name);
unregisterBorrowsFromValue(removed);
found = true;
}
}
Expand All @@ -461,6 +473,29 @@ public ExecutionContext copyWithVariable(String name, Object value, String type)

return new ExecutionContext(objectInstance, newLocals, slotValues, slotTypes, typeHandler);
}

public void setObjectField(String fieldName, Object value) {
if (fieldName == null) {
throw new InternalError("setObjectField called with null fieldName");
}
if (objectInstance == null || objectInstance.fields == null) {
throw new InternalError("setObjectField called outside object context");
}
Object previous = objectInstance.fields.put(fieldName, value);
replaceTrackedValue(previous, value);
}

public boolean hasActiveBorrow(Object container, long index) {
if (container == null) return false;
Map<Long, Integer> countsByIndex = activeBorrowsByContainer.get(container);
if (countsByIndex == null) return false;
Integer count = countsByIndex.get(index);
return count != null && count > 0;
}

public void trackValueReplacement(Object oldValue, Object newValue) {
replaceTrackedValue(oldValue, newValue);
}

// Clear slot optimization (if slots change)
public void rebuildSlotOptimization() {
Expand All @@ -471,4 +506,76 @@ public void rebuildSlotOptimization() {
this.slotTypesList = null;
optimizeSlotAccess();
}

private void registerInitialBorrowState(Map<String, Object> initialLocals) {
if (initialLocals != null) {
for (Object value : initialLocals.values()) {
registerBorrowsFromValue(value);
}
}
if (slotValues != null) {
for (Object value : slotValues.values()) {
registerBorrowsFromValue(value);
}
}
if (objectInstance != null && objectInstance.fields != null) {
for (Object value : objectInstance.fields.values()) {
registerBorrowsFromValue(value);
}
}
}

private void replaceTrackedValue(Object oldValue, Object newValue) {
unregisterBorrowsFromValue(oldValue);
registerBorrowsFromValue(newValue);
}

private void registerBorrowsFromValue(Object value) {
collectBorrowsRecursive(value, 1);
}

private void unregisterBorrowsFromValue(Object value) {
collectBorrowsRecursive(value, -1);
}

@SuppressWarnings("unchecked")
private void collectBorrowsRecursive(Object value, int delta) {
if (value == null) return;
Object unwrapped = typeHandler.unwrap(value);
if (unwrapped == null) return;

if (unwrapped instanceof TypeHandler.PointerValue) {
TypeHandler.PointerValue pointer = (TypeHandler.PointerValue) unwrapped;
updateBorrowCount(pointer.container, pointer.index, delta);
return;
}

if (unwrapped instanceof List) {
for (Object element : (List<Object>) unwrapped) {
collectBorrowsRecursive(element, delta);
}
}
}

private void updateBorrowCount(Object container, long index, int delta) {
if (container == null || delta == 0) return;

Map<Long, Integer> countsByIndex = activeBorrowsByContainer.get(container);
if (countsByIndex == null) {
if (delta < 0) return;
countsByIndex = new HashMap<Long, Integer>();
activeBorrowsByContainer.put(container, countsByIndex);
}

Integer current = countsByIndex.get(index);
int next = (current != null ? current : 0) + delta;
if (next > 0) {
countsByIndex.put(index, next);
} else {
countsByIndex.remove(index);
if (countsByIndex.isEmpty()) {
activeBorrowsByContainer.remove(container);
}
}
}
}
61 changes: 9 additions & 52 deletions src/main/java/cod/interpreter/handler/AssignmentHandler.java
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Original file line number Diff line number Diff line change
Expand Up @@ -189,15 +189,18 @@ private Object handleIndexAssignment(IndexAccess indexAccess, Object newValue, E
NaturalArray natural = (NaturalArray) arrayObj;
long index = expressionHandler.toLongIndex(indexObj);
ensureNoActiveBorrow(arrayObj, index, ctx);
Object previous = natural.get(index);
natural.set(index, newValue);
ctx.trackValueReplacement(previous, newValue);
return newValue;
}

if (arrayObj instanceof List) {
int intIndex = expressionHandler.toIntIndex(indexObj);
ensureNoActiveBorrow(arrayObj, intIndex, ctx);
List<Object> list = (List<Object>) arrayObj;
list.set(intIndex, newValue);
Object previous = list.set(intIndex, newValue);
ctx.trackValueReplacement(previous, newValue);
return newValue;
}

Expand Down Expand Up @@ -338,15 +341,7 @@ private void ensureNoActiveBorrow(Object container, long index, ExecutionContext
if (!isBorrowCheckerActive(ctx)) {
return;
}
if (hasBorrowInLocals(container, index, ctx.getLocalsStack())) {
throwBorrowMutationViolation(index);
}
if (ctx.objectInstance != null
&& ctx.objectInstance.fields != null
&& hasBorrowInMap(container, index, ctx.objectInstance.fields)) {
throwBorrowMutationViolation(index);
}
if (ctx.getSlotValues() != null && hasBorrowInMap(container, index, ctx.getSlotValues())) {
if (ctx.hasActiveBorrow(container, index)) {
throwBorrowMutationViolation(index);
}
}
Expand All @@ -359,44 +354,6 @@ private boolean isBorrowCheckerActive(ExecutionContext ctx) {
return ctx != null && (ctx.isUnsafeExecutionContext() || (ctx.currentClass != null && ctx.currentClass.isUnsafe));
}

private boolean hasBorrowInLocals(Object container, long index, List<Map<String, Object>> scopes) {
if (scopes == null) return false;
for (Map<String, Object> scope : scopes) {
if (hasBorrowInMap(container, index, scope)) {
return true;
}
}
return false;
}

private boolean hasBorrowInMap(Object container, long index, Map<String, Object> values) {
if (values == null || values.isEmpty()) return false;
for (Object value : values.values()) {
if (containsBorrowForLocation(typeSystem.unwrap(value), container, index)) {
return true;
}
}
return false;
}

@SuppressWarnings("unchecked")
private boolean containsBorrowForLocation(Object value, Object container, long index) {
if (value == null) return false;
if (value instanceof TypeHandler.PointerValue) {
TypeHandler.PointerValue pointer = (TypeHandler.PointerValue) value;
return pointer.container == container && pointer.index == index;
}
if (value instanceof List) {
List<Object> list = (List<Object>) value;
for (Object element : list) {
if (containsBorrowForLocation(typeSystem.unwrap(element), container, index)) {
return true;
}
}
}
return false;
}

private Object handleVariableAssignment(Expr target, Object newValue, ExecutionContext ctx) {
try {
if (target instanceof PropertyAccess) {
Expand Down Expand Up @@ -459,7 +416,7 @@ public Object assignToVariableScoped(String varName, Object newValue, ExecutionC
if (NamingValidator.isAllCaps(varName)) {
throw new ProgramError("Cannot reassign constant field '" + varName + "'");
}
ctx.objectInstance.fields.put(varName, newValue);
ctx.setObjectField(varName, newValue);
return newValue;
}
}
Expand All @@ -484,7 +441,7 @@ private Object updateVariableInScope(String varName, Object newValue,
newValue = typeSystem.wrapUnionType(newValue, declaredType);
}

scope.put(varName, newValue);
ctx.setVariable(varName, newValue);
return newValue;
} catch (ProgramError e) {
throw e;
Expand All @@ -501,7 +458,7 @@ private Object assignToField(String fieldName, Object newValue, ExecutionContext
if (NamingValidator.isAllCaps(fieldName)) {
throw new ProgramError("Cannot reassign constant field '" + fieldName + "'");
}
ctx.objectInstance.fields.put(fieldName, newValue);
ctx.setObjectField(fieldName, newValue);
return newValue;
} else {
throw new ProgramError("Cannot assign to undefined field via this: " + fieldName);
Expand Down Expand Up @@ -535,7 +492,7 @@ private Object assignToSuperField(String fieldName, Object newValue, ExecutionCo
if (NamingValidator.isAllCaps(fieldName)) {
throw new ProgramError("Cannot reassign constant field '" + fieldName + "'");
}
ctx.objectInstance.fields.put(fieldName, newValue);
ctx.setObjectField(fieldName, newValue);
return newValue;
}
throw new ProgramError("Cannot assign to undefined field via super: " + fieldName);
Expand Down