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I guess the simplest example is shared memory between processes. Even Python has it: https://docs.python.org/3/library/multiprocessing.shared_memory.html https
by knuthsat 5y ago
I guess the simplest example is shared memory between processes.
Even Python has it: https://docs.python.org/3/library/multiprocessing.shared_memory.html https://docs.python.org/3/library/multiprocessing.shared_mem...
- SCHiM 5y agoAccess to raw memory is locked behind the unsafe keyword though. Rust officially already does not guarantee any safety in that scenario even within 1 process.
- pjmlp 5y agoThere is always unsafe at some level on the standard library. The point is that it doesn't protect the user of a crate that only exposes a fully safe API, unless they do digging to validate overall architecture safety.
- KptMarchewa 5y ago>Even Python It's not "even". Python specifically has it because it has no real threading.
- bjourne 5y agoPython has cooperative threading. It's the same threading model used in the Erlang VM, Julia and many other dynamically typed languages. But preemptive threading vs. cooperative threading is orthogonal to whether data races can happen. Java threads are preemptive but data races can still happen.
- nesarkvechnep 5y agoThe Erlang VM does preemptive scheduling.
- bjourne 5y agoNo it doesn't.
- grogers 5y agoWhile this is technically true it's quite misleading. The VM itself uses cooperative scheduling, but the Erlang compiler emits something akin to yields appropriately, such the net effect is preemptive scheduling. You can break it by calling a NIF that doesn't do the yields appropriately, but that's not the norm.
- bjourne 5y agoPreemptive threading means that the running thread can be paused by the system without ANY cooperation from the thread itself. Emphasis on "any". Python works roughly the same as Erlang. Every N bytecodes it checks if a thread is waiting to run and switches to that. Both are variants of cooperative threading.
- dangerbird2 5y agoPython does have real threading. The `threading` module provides os-level threads and synchronization primitives. The only difference between this and multithreading in C or Java is that CPython's GIL prevents more than one thread executing bytecode at a time. This prevents parallelism, but not concurrency. Note this does not mean that python code is thread-safe by default. At most, you can theoretically rely on bytecode operations to be atomic, which means you'll need to synchronize multi-threaded code with mutexes, semaphores and higher-level synchronization constructs.
- knuthsat 5y agoSharedMemory is a new thing in Python. Not even supported by all 3.x versions.
- berkes 5y agoBut this is specifically about Rust. What data races between processes, other than Disk/IO, databases, or external services, can a Rust program have? I explicitely exclude the whole category of external services, since that is "by design" really. And the whole reason for ACID, global mutexes, transactions and CRDTs.