Scoped Threads

Normal threads cannot borrow from their environment:

rust,editable,compile_fail

# // Copyright 2024 Google LLC
# // SPDX-License-Identifier: Apache-2.0
#
use std::thread;

fn foo() {
    let s = String::from("Hello");
    thread::spawn(|| {
        dbg!(s.len());
    });
}

fn main() {
    foo();
}

However, you can use a scoped thread for this:

rust,editable

# // Copyright 2024 Google LLC
# // SPDX-License-Identifier: Apache-2.0
#
use std::thread;

fn foo() {
    let s = String::from("Hello");
    thread::scope(|scope| {
        scope.spawn(|| {
            dbg!(s.len());
        });
    });
}

fn main() {
    foo();
}

The reason for that is that when the thread::scope function completes, all the threads are guaranteed to be joined, so they can return borrowed data.
Normal Rust borrowing rules apply: you can either borrow mutably by one thread, or immutably by any number of threads.

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