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| -rw-r--r-- | src/doc/book/concurrency.md | 7 |
1 files changed, 6 insertions, 1 deletions
diff --git a/src/doc/book/concurrency.md b/src/doc/book/concurrency.md index 87d551b68df..82d2de7e3bf 100644 --- a/src/doc/book/concurrency.md +++ b/src/doc/book/concurrency.md @@ -164,7 +164,7 @@ The same [ownership system](ownership.html) that helps prevent using pointers incorrectly also helps rule out data races, one of the worst kinds of concurrency bugs. -As an example, here is a Rust program that would have a data race in many +As an example, here is a Rust program that could have a data race in many languages. It will not compile: ```ignore @@ -197,6 +197,11 @@ thread, and the thread takes ownership of the reference, we'd have three owners! `data` gets moved out of `main` in the first call to `spawn()`, so subsequent calls in the loop cannot use this variable. +Note that this specific example will not cause a data race since different array +indices are being accessed. But this can't be determined at compile time, and in +a similar situation where `i` is a constant or is random, you would have a data +race. + So, we need some type that lets us have more than one owning reference to a value. Usually, we'd use `Rc<T>` for this, which is a reference counted type that provides shared ownership. It has some runtime bookkeeping that keeps track |