malloc and printf usually use global structures, and employ lock-based synchronization internally. That’s why they’re not reentrant. The malloc function could either be thread-safe or thread-unsafe. Both are not reentrant: Malloc operates on a global heap, and it’s possible that two different invocations of malloc that happen at the same time, return the same memory … Read more
TL;DR: A function can be reentrant, thread-safe, both or neither. The Wikipedia articles for thread-safety and reentrancy are well worth reading. Here are a few citations: A function is thread-safe if: it only manipulates shared data structures in a manner that guarantees safe execution by multiple threads at the same time. A function is reentrant … Read more
1. How is safely defined? Semantically. In this case, this is not a hard-defined term. It just mean “You can do that, without risk”. 2. If a program can be safely executed concurrently, does it always mean that it is reentrant? No. For example, let’s have a C++ function that takes both a lock, and … Read more
No event will ever occur while a process is running! When a process is woken by an event, it runs to completion (“end process”) or an explicit “wait” statement, and goes to sleep. This takes, notionally, ZERO time. Which means that if you have loops in your process, they are effectively unrolled completely, and when … Read more