[c] re entrancy and thread safty

• see

• reentrancy

  • "A function is reentrant if it can be invoked while already in the process of executing. That is, a function is reentrant if it can be interrupted in the middle of execution (for example, by a signal or interrupt) and invoked again before the interrupted execution completes."
  • "A reentrant function can be invoked, interrupted, and re-invoked. Such a function can be invoked simultaneously by multiple threads if and only if each invocation references or provides unique data and inputs."
  • "The term reentrancy predates threads and is often used only in a single threaded context, for example when discussing if a function is signal or interrupt-safe."
  • reentrancy는 기본적으로 single thread에서 논의되는 개념이다. function의 실행 도중에 signal이나 interrupt를 받아 중지되었을 때, 다시 재개(re-enter)해도 동일한 결과를 보장하는가? 그리고 이 개념을 multi thread 환경으로 확장한다고 해도 마찬가지여야 한다.

• thread-safty

  • "A thread-safe function can be invoked simultaneously by multiple threads, even if each invocation references or provides the same data or input, as all access is serialized."
  • tread-safty는 여러개의 thread가 동시에 function을 실행시켜도 동기화 문제가 없다는 개념이다.
  • "a thread-safe function that achieves safety through a mutex is potentially not reentrant, as the interruption could deadlock on the already-acquired mutex."
  • function이 mutex 등을 통해서 동기화하기 때문에 thread-safe하다고 해도, 잠재적으로 reentrant하지는 않다