memory-safety-patterns

Memory Safety Patterns

Cross-language patterns for memory-safe programming including RAII, ownership, smart pointers, and resource management.

When to Use This Skill

• Writing memory-safe systems code
• Managing resources (files, sockets, memory)
• Preventing use-after-free and leaks
• Implementing RAII patterns
• Choosing between languages for safety
• Debugging memory issues

Core Concepts

1. Memory Bug Categories

Bug Type	Description	Prevention
Use-after-free	Access freed memory	Ownership, RAII
Double-free	Free same memory twice	Smart pointers
Memory leak	Never free memory	RAII, GC
Buffer overflow	Write past buffer end	Bounds checking
Dangling pointer	Pointer to freed memory	Lifetime tracking
Data race	Concurrent unsynchronized access	Ownership, Sync

2. Safety Spectrum

Manual (C) → Smart Pointers (C++) → Ownership (Rust) → GC (Go, Java)
Less safe                                              More safe
More control                                           Less control

Patterns by Language

Pattern 1: RAII in C++

// RAII: Resource Acquisition Is Initialization
// Resource lifetime tied to object lifetime

#include <memory>
#include <fstream>
#include <mutex>

// File handle with RAII
class FileHandle {
public:
    explicit FileHandle(const std::string& path)
        : file_(path) {
        if (!file_.is_open()) {
            throw std::runtime_error("Failed to open file");
        }
    }

    // Destructor automatically closes file
    ~FileHandle() = default; // fstream closes in its destructor

    // Delete copy (prevent double-close)
    FileHandle(const FileHandle&) = delete;
    FileHandle& operator=(const FileHandle&) = delete;

    // Allow move
    FileHandle(FileHandle&&) = default;
    FileHandle& operator=(FileHandle&&) = default;

    void write(const std::string& data) {
        file_ << data;
    }

private:
    std::fstream file_;
};

// Lock guard (RAII for mutexes)
class Database {
public:
    void update(const std::string& key, const std::string& value) {
        std::lock_guard<std::mutex> lock(mutex_); // Released on scope exit
        data_[key] = value;
    }

    std::string get(const std::string& key) {
        std::shared_lock<std::shared_mutex> lock(shared_mutex_);
        return data_[key];
    }

private:
    std::mutex mutex_;
    std::shared_mutex shared_mutex_;
    std::map<std::string, std::string> data_;
};

// Transaction with rollback (RAII)
template<typename T>
class Transaction {
public:
    explicit Transaction(T& target)
        : target_(target), backup_(target), committed_(false) {}

    ~Transaction() {
        if (!committed_) {
            target_ = backup_; // Rollback
        }
    }

    void commit() { committed_ = true; }

    T& get() { return target_; }

private:
    T& target_;
    T backup_;
    bool committed_;
};