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Auto merge of #59879 - ebarnard:patch-1, r=alexcrichton

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Add a comment explaining why SecRandomCopyBytes is not used on MacOS

SecRandomCopyBytes is [available since MacOS 10.7](https://developer.apple.com/documentation/security/1399291-secrandomcopybytes?language=objc) which is the minimum supported version and which was suggested in https://github.com/rust-lang/rust/pull/58901#issuecomment-470188115 is the earliest version currently in use.

This matches the behaviour of other platforms which have a random number generator syscall available.
This commit is contained in:
bors 2019-04-16 16:04:12 +00:00
commit 70f130954d
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7
src/libstd/sys/unix/rand.rs
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@ -99,6 +99,13 @@ mod imp {
}
}
// On iOS and MacOS `SecRandomCopyBytes` calls `CCRandomCopyBytes` with
// `kCCRandomDefault`. `CCRandomCopyBytes` manages a CSPRNG which is seeded
// from `/dev/random` and which runs on its own thread accessed via GCD.
// This seems needlessly heavyweight for the purposes of generating two u64s
// once per thread in `hashmap_random_keys`. Therefore `SecRandomCopyBytes` is
// only used on iOS where direct access to `/dev/urandom` is blocked by the
// sandbox.
#[cfg(target_os = "ios")]
mod imp {
use crate::io;