Stack Overflow from Deep Recursion

TL;DR

Explanation

PHP's call stack is limited by the OS stack size (typically 8MB on Linux). Deep recursion exhausts it and causes a segfault or memory_limit error — neither is catchable with try/catch. Practical limit is roughly 500–5000 nested calls depending on frame size. Solutions: convert tail-recursive functions to iterative loops, use a trampoline pattern, or process trees iteratively with an explicit stack (SplStack). xdebug.max_nesting_level (default 256) provides an earlier, catchable limit via E_ERROR.

Common Misconception

Why It Matters

Common Mistakes

• Recursive tree traversal without depth limit.
• Not converting obvious tail recursion to iteration.
• Setting xdebug.max_nesting_level too high — delays the crash.

Code Examples

function factorial(int $n): int {
    return $n <= 1 ? 1 : $n * factorial($n - 1);
}
factorial(100000); // Segfault

function factorial(int $n): int {
    $result = 1;
    for ($i = 2; $i <= $n; $i++) $result *= $i;
    return $result;
}

// Iterative tree traversal using explicit stack
function traverse(Node $root): void {
    $stack = new \SplStack();
    $stack->push($root);
    while (!$stack->isEmpty()) {
        $node = $stack->pop();
        process($node);
        foreach ($node->children as $child) $stack->push($child);
    }
}

References

• ↗ https://www.php.net/manual/en/function.xdebug-get-stack-depth.php

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