Infinite Loop Detection
Analyze PHP code for potential infinite loops and unbounded execution.
Detection Patterns
1. Missing Break Conditions
php
// BUG: No exit condition
while (true) {
$item = $queue->pop();
process($item);
// No break when queue is empty
}
// BUG: Condition never changes
$running = true;
while ($running) {
doWork();
// $running never set to false
}
// BUG: Break inside nested condition
while ($items) {
foreach ($items as $item) {
if ($item->isDone()) {
break; // Only breaks inner loop
}
}
}
2. Incorrect Loop Variable Modification
php
// BUG: Wrong variable incremented
for ($i = 0; $i < count($items); $j++) { // Should be $i++
process($items[$i]);
}
// BUG: Variable modified in wrong direction
for ($i = 10; $i > 0; $i++) { // Should be $i--
process($i);
}
// BUG: Loop variable reset
$i = 0;
while ($i < 10) {
if ($condition) {
$i = 0; // Resets counter
}
$i++;
}
3. Unbounded Recursion
php
// BUG: No base case
function factorial(int $n): int
{
return $n * factorial($n - 1); // Never stops
}
// BUG: Base case unreachable
function traverse(Node $node): void
{
$this->traverse($node->getNext()); // What if getNext returns self?
// Missing: if ($node === null) return;
}
// BUG: Mutual recursion
function a($n) { return b($n); }
function b($n) { return a($n); } // Infinite cycle
4. Circular References
php
// BUG: Circular linked list traversal
while ($node !== null) {
$node = $node->next; // What if list is circular?
}
// BUG: Object graph cycle
function serialize($obj, $visited = []): string
{
foreach ($obj->getRelations() as $rel) {
$result .= serialize($rel); // May revisit objects
}
}
// FIXED:
function serialize($obj, array &$visited = []): string
{
if (in_array($obj, $visited, true)) {
return '[circular]';
}
$visited[] = $obj;
// ...
}
5. Event/Listener Loops
php
// BUG: Event triggers itself
class UserUpdatedListener
{
public function handle(UserUpdated $event): void
{
$user = $event->getUser();
$user->touch(); // Triggers another UserUpdated event
}
}
// BUG: Message queue requeue loop
public function handle(Message $message): void
{
try {
$this->process($message);
} catch (Exception $e) {
$this->queue->publish($message); // Requeues failed message infinitely
}
}
6. Retry Without Limit
php
// BUG: Infinite retry
function fetch(string $url): string
{
while (true) {
try {
return $this->httpClient->get($url);
} catch (Exception $e) {
sleep(1);
// No max retries, infinite loop on persistent failure
}
}
}
// FIXED:
function fetch(string $url, int $maxRetries = 3): string
{
$attempts = 0;
while ($attempts < $maxRetries) {
try {
return $this->httpClient->get($url);
} catch (Exception $e) {
$attempts++;
if ($attempts >= $maxRetries) {
throw $e;
}
sleep(1);
}
}
}
7. Generator Infinite Yield
php
// BUG: Generator never ends
function allNumbers(): Generator
{
$i = 0;
while (true) {
yield $i++;
// Fine for generators, but consuming code may not limit
}
}
// Usage BUG:
foreach (allNumbers() as $n) {
echo $n; // Infinite loop
}
8. Database Pagination Without Limit
php
// BUG: Potentially infinite
$offset = 0;
while (true) {
$batch = $repository->findBy([], null, 100, $offset);
if (empty($batch)) {
break;
}
process($batch);
// Missing: $offset += 100;
}
Grep Patterns
bash
# while(true) without break
Grep: "while\s*\(\s*true\s*\)" --glob "**/*.php"
# Recursion
Grep: "function\s+(\w+)\([^)]*\)[^{]*\{[^}]*\1\s*\(" --glob "**/*.php"
# for loop with wrong increment
Grep: "for\s*\([^;]+;\s*\$\w+\s*[<>]\s*[^;]+;\s*\$(?!\1)" --glob "**/*.php"
# while without modification
Grep: "while\s*\(\s*\$\w+\s*\)" --glob "**/*.php"
Severity Classification
| Pattern | Severity | |
|---|
| Infinite retry without limit | 🔴 Critical | |
| Missing recursion base case | 🔴 Critical | |
| Wrong loop variable | 🔴 Critical | |
| Circular reference traversal | 🟠 Major | |
| Event self-triggering | 🟠 Major | |
| while(true) without clear exit | 🟠 Major | |
Prevention Patterns
Always Use Limits
php
const MAX_ITERATIONS = 1000;
$iterations = 0;
while ($condition && $iterations < self::MAX_ITERATIONS) {
// ...
$iterations++;
}
if ($iterations >= self::MAX_ITERATIONS) {
throw new RuntimeException('Max iterations exceeded');
}
Track Visited Nodes
php
function traverse($node, array &$visited = []): void
{
$id = spl_object_id($node);
if (isset($visited[$id])) {
return;
}
$visited[$id] = true;
// ...
}
Recursion Depth Limit
php
function process($data, int $depth = 0): mixed
{
if ($depth > 100) {
throw new RuntimeException('Max recursion depth');
}
return process($child, $depth + 1);
}
Output Format
markdown
### Infinite Loop Risk: [Description]
**Severity:** 🔴/🟠/🟡
**Location:** `file.php:line`
**Type:** [Missing Break|Wrong Variable|Unbounded Recursion|...]
**Issue:**
[Description of how infinite loop can occur]
**Code:**
// Problematic code
// With proper termination
**Trigger Condition:**
[When this infinite loop would occur]