RAII (Resource Acquisition Is Initialization)

Use case

Automatically release a lock on shared disassembler cache when leaving scope.

Explanation

RAII ties resource lifetime to object lifetime. Constructor acquires, destructor releases. Guarantees cleanup even on exceptions.

Code

#include <cstdint>
#include <mutex>
#include <print>

std::mutex g_cache_mutex;

class CacheLock {
public:
  CacheLock(std::mutex &m) : mutex_(m) {
    mutex_.lock();
    std::println("Cache locked.");
  }

  ~CacheLock() {
    mutex_.unlock();
    std::println("Cache unlocked.");
  }

private:
  std::mutex &mutex_;
};

void disassemble(uint64_t addr) {
  CacheLock lock(g_cache_mutex);
  std::println("Disassembling {:#x}...", addr);
}

int main() {
  disassemble(0x10001000);
  disassemble(0x10002000);
  return 0;
}

View on GitHub.

Output

$ ./src/design-patterns-and-idioms/build/raii
Cache locked.
Disassembling 0x10001000...
Cache unlocked.
Cache locked.
Disassembling 0x10002000...
Cache unlocked.