The initialization of CONTEXT in shared_context() is not thread-safe. Multiple threads calling shared_context() can end up using an un-initialized CONTEXT before the thread that successfully calls compare_exchange can fully initialize CONTEXT.
|
#[cfg(all(any(feature = "v1", feature = "v6"), feature = "std", feature = "rng"))] |
|
static CONTEXT: Context = Context { |
|
count: Atomic::new(0), |
|
}; |
|
|
|
#[cfg(all(any(feature = "v1", feature = "v6"), feature = "std", feature = "rng"))] |
|
static CONTEXT_INITIALIZED: Atomic<bool> = Atomic::new(false); |
|
|
|
#[cfg(all(any(feature = "v1", feature = "v6"), feature = "std", feature = "rng"))] |
|
pub(crate) fn shared_context() -> &'static Context { |
|
// If the context is in its initial state then assign it to a random value |
|
// It doesn't matter if multiple threads observe `false` here and initialize the context |
|
if CONTEXT_INITIALIZED |
|
.compare_exchange(false, true, Ordering::Relaxed, Ordering::Relaxed) |
|
.is_ok() |
|
{ |
|
CONTEXT.count.store(crate::rng::u16(), Ordering::Release); |
|
} |
|
|
|
&CONTEXT |
|
} |
Here is an example that demonstrates the problem:
use std::thread;
use uuid::Uuid;
fn main() {
let threads: Vec<thread::JoinHandle<()>> = (0..10).map(|i| {
thread::spawn(move || {
let node_id: [u8; 6] = [ 1, 2, 3, 4, 5, 6 ];
let uuid = Uuid::now_v6(&node_id);
let counter = uuid.get_timestamp().unwrap().to_rfc4122().1;
println!("Hello from thread {i} - uuid: {uuid} - counter: {counter}!");
})
}).collect();
threads.into_iter().for_each(|t| t.join().unwrap() );
}Here are a few runs from an Macbook Pro M1 (arm64). You can see some of the threads are starting from the un-initialized value of 0 and counting from there before the thread that successfully runs the compare_exchange is able to actually initialized CONTEXT with a random value:
» cargo run
Finished dev [unoptimized + debuginfo] target(s) in 0.01s
Running `target/debug/weather`
Hello from thread 2 - uuid: 1eeb8a59-b9dc-66ca-8000-010203040506 - counter: 0!
Hello from thread 1 - uuid: 1eeb8a59-b9dc-6864-8002-010203040506 - counter: 2!
Hello from thread 3 - uuid: 1eeb8a59-b9dc-67c4-8001-010203040506 - counter: 1!
Hello from thread 0 - uuid: 1eeb8a59-b9dc-6968-87f3-010203040506 - counter: 2035!
Hello from thread 4 - uuid: 1eeb8a59-b9dc-6b52-87f4-010203040506 - counter: 2036!
Hello from thread 6 - uuid: 1eeb8a59-b9dc-6b7a-87f5-010203040506 - counter: 2037!
Hello from thread 5 - uuid: 1eeb8a59-b9dc-6c60-87f6-010203040506 - counter: 2038!
Hello from thread 7 - uuid: 1eeb8a59-b9dc-6daa-87f7-010203040506 - counter: 2039!
Hello from thread 8 - uuid: 1eeb8a59-b9dc-6e86-87f8-010203040506 - counter: 2040!
Hello from thread 9 - uuid: 1eeb8a59-b9dc-6f6c-87f9-010203040506 - counter: 2041!
» cargo run
Finished dev [unoptimized + debuginfo] target(s) in 0.01s
Running `target/debug/weather`
Hello from thread 2 - uuid: 1eeb8a59-c4ae-617a-8000-010203040506 - counter: 0!
Hello from thread 1 - uuid: 1eeb8a59-c4ae-61c0-8001-010203040506 - counter: 1!
Hello from thread 4 - uuid: 1eeb8a59-c4ae-642c-8002-010203040506 - counter: 2!
Hello from thread 3 - uuid: 1eeb8a59-c4ae-6440-8003-010203040506 - counter: 3!
Hello from thread 5 - uuid: 1eeb8a59-c4ae-64a4-8004-010203040506 - counter: 4!
Hello from thread 0 - uuid: 1eeb8a59-c4ae-65ee-8e52-010203040506 - counter: 3666!
Hello from thread 7 - uuid: 1eeb8a59-c4ae-6936-8e53-010203040506 - counter: 3667!
Hello from thread 6 - uuid: 1eeb8a59-c4ae-6936-8e54-010203040506 - counter: 3668!
Hello from thread 8 - uuid: 1eeb8a59-c4ae-6ada-8e55-010203040506 - counter: 3669!
Hello from thread 9 - uuid: 1eeb8a59-c4ae-6bfc-8e56-010203040506 - counter: 3670!
» cargo run
Finished dev [unoptimized + debuginfo] target(s) in 0.01s
Running `target/debug/weather`
Hello from thread 1 - uuid: 1eeb8a59-e1dc-6918-8000-010203040506 - counter: 0!
Hello from thread 2 - uuid: 1eeb8a59-e1dc-6af8-8002-010203040506 - counter: 2!
Hello from thread 4 - uuid: 1eeb8a59-e1dc-6dbe-8003-010203040506 - counter: 3!
Hello from thread 5 - uuid: 1eeb8a59-e1dc-6e2c-8004-010203040506 - counter: 4!
Hello from thread 3 - uuid: 1eeb8a59-e1dc-6af8-8001-010203040506 - counter: 1!
Hello from thread 6 - uuid: 1eeb8a59-e1dd-61ce-8005-010203040506 - counter: 5!
Hello from thread 7 - uuid: 1eeb8a59-e1dd-625a-8006-010203040506 - counter: 6!
Hello from thread 8 - uuid: 1eeb8a59-e1dd-6304-8007-010203040506 - counter: 7!
Hello from thread 0 - uuid: 1eeb8a59-e1dd-6372-a008-010203040506 - counter: 8200!
Hello from thread 9 - uuid: 1eeb8a59-e1dd-639a-a009-010203040506 - counter: 8201!Here are some runs from an Intel Core i7 (x86_64):
$ cargo run
Finished dev [unoptimized + debuginfo] target(s) in 0.01s
Running `target/debug/weather`
Hello from thread 3 - uuid: 1eeb8a89-27dc-6f82-8000-010203040506 - counter: 0!
Hello from thread 1 - uuid: 1eeb8a89-27dd-6060-8002-010203040506 - counter: 2!
Hello from thread 0 - uuid: 1eeb8a89-27dc-6f81-8001-010203040506 - counter: 1!
Hello from thread 4 - uuid: 1eeb8a89-27dd-66b4-8003-010203040506 - counter: 3!
Hello from thread 5 - uuid: 1eeb8a89-27dd-6c9b-8004-010203040506 - counter: 4!
Hello from thread 2 - uuid: 1eeb8a89-27de-604a-a68e-010203040506 - counter: 9870!
Hello from thread 7 - uuid: 1eeb8a89-27de-61e2-a68f-010203040506 - counter: 9871!
Hello from thread 6 - uuid: 1eeb8a89-27de-63e0-a690-010203040506 - counter: 9872!
Hello from thread 8 - uuid: 1eeb8a89-27de-6485-a691-010203040506 - counter: 9873!
Hello from thread 9 - uuid: 1eeb8a89-27de-674c-a692-010203040506 - counter: 9874!
$ cargo run
Finished dev [unoptimized + debuginfo] target(s) in 0.01s
Running `target/debug/weather`
Hello from thread 2 - uuid: 1eeb8a89-904f-6bd7-8001-010203040506 - counter: 1!
Hello from thread 1 - uuid: 1eeb8a89-904f-6bd5-8000-010203040506 - counter: 0!
Hello from thread 3 - uuid: 1eeb8a89-904f-6be2-8003-010203040506 - counter: 3!
Hello from thread 4 - uuid: 1eeb8a89-904f-6bd5-8002-010203040506 - counter: 2!
Hello from thread 5 - uuid: 1eeb8a89-9050-6809-8004-010203040506 - counter: 4!
Hello from thread 0 - uuid: 1eeb8a89-9050-6b45-b4cd-010203040506 - counter: 13517!
Hello from thread 6 - uuid: 1eeb8a89-9051-6243-b4ce-010203040506 - counter: 13518!
Hello from thread 8 - uuid: 1eeb8a89-9051-648c-b4cf-010203040506 - counter: 13519!
Hello from thread 7 - uuid: 1eeb8a89-9051-651d-b4d0-010203040506 - counter: 13520!
Hello from thread 9 - uuid: 1eeb8a89-9051-67fa-b4d1-010203040506 - counter: 13521!
$ cargo run
Finished dev [unoptimized + debuginfo] target(s) in 0.01s
Running `target/debug/weather`
Hello from thread 1 - uuid: 1eeb8a89-ff0e-6a0d-8001-010203040506 - counter: 1!
Hello from thread 2 - uuid: 1eeb8a89-ff0e-6a0d-8002-010203040506 - counter: 2!
Hello from thread 3 - uuid: 1eeb8a89-ff0e-6a0b-8000-010203040506 - counter: 0!
Hello from thread 4 - uuid: 1eeb8a89-ff0f-60ac-8003-010203040506 - counter: 3!
Hello from thread 5 - uuid: 1eeb8a89-ff0f-65aa-8004-010203040506 - counter: 4!
Hello from thread 0 - uuid: 1eeb8a89-ff0f-671d-9d90-010203040506 - counter: 7568!
Hello from thread 6 - uuid: 1eeb8a89-ff0f-6999-9d91-010203040506 - counter: 7569!
Hello from thread 9 - uuid: 1eeb8a89-ff0f-6cc4-9d92-010203040506 - counter: 7570!
Hello from thread 7 - uuid: 1eeb8a89-ff0f-6ddf-9d93-010203040506 - counter: 7571!
Hello from thread 8 - uuid: 1eeb8a89-ff0f-6fdb-9d94-010203040506 - counter: 7572!
The initialization of
CONTEXTinshared_context()is not thread-safe. Multiple threads callingshared_context()can end up using an un-initializedCONTEXTbefore the thread that successfully callscompare_exchangecan fully initializeCONTEXT.uuid/src/timestamp.rs
Lines 372 to 392 in cefc353
Here is an example that demonstrates the problem:
Here are a few runs from an Macbook Pro M1 (arm64). You can see some of the threads are starting from the un-initialized value of 0 and counting from there before the thread that successfully runs the
compare_exchangeis able to actually initializedCONTEXTwith a random value:» cargo run Finished dev [unoptimized + debuginfo] target(s) in 0.01s Running `target/debug/weather` Hello from thread 2 - uuid: 1eeb8a59-b9dc-66ca-8000-010203040506 - counter: 0! Hello from thread 1 - uuid: 1eeb8a59-b9dc-6864-8002-010203040506 - counter: 2! Hello from thread 3 - uuid: 1eeb8a59-b9dc-67c4-8001-010203040506 - counter: 1! Hello from thread 0 - uuid: 1eeb8a59-b9dc-6968-87f3-010203040506 - counter: 2035! Hello from thread 4 - uuid: 1eeb8a59-b9dc-6b52-87f4-010203040506 - counter: 2036! Hello from thread 6 - uuid: 1eeb8a59-b9dc-6b7a-87f5-010203040506 - counter: 2037! Hello from thread 5 - uuid: 1eeb8a59-b9dc-6c60-87f6-010203040506 - counter: 2038! Hello from thread 7 - uuid: 1eeb8a59-b9dc-6daa-87f7-010203040506 - counter: 2039! Hello from thread 8 - uuid: 1eeb8a59-b9dc-6e86-87f8-010203040506 - counter: 2040! Hello from thread 9 - uuid: 1eeb8a59-b9dc-6f6c-87f9-010203040506 - counter: 2041! » cargo run Finished dev [unoptimized + debuginfo] target(s) in 0.01s Running `target/debug/weather` Hello from thread 2 - uuid: 1eeb8a59-c4ae-617a-8000-010203040506 - counter: 0! Hello from thread 1 - uuid: 1eeb8a59-c4ae-61c0-8001-010203040506 - counter: 1! Hello from thread 4 - uuid: 1eeb8a59-c4ae-642c-8002-010203040506 - counter: 2! Hello from thread 3 - uuid: 1eeb8a59-c4ae-6440-8003-010203040506 - counter: 3! Hello from thread 5 - uuid: 1eeb8a59-c4ae-64a4-8004-010203040506 - counter: 4! Hello from thread 0 - uuid: 1eeb8a59-c4ae-65ee-8e52-010203040506 - counter: 3666! Hello from thread 7 - uuid: 1eeb8a59-c4ae-6936-8e53-010203040506 - counter: 3667! Hello from thread 6 - uuid: 1eeb8a59-c4ae-6936-8e54-010203040506 - counter: 3668! Hello from thread 8 - uuid: 1eeb8a59-c4ae-6ada-8e55-010203040506 - counter: 3669! Hello from thread 9 - uuid: 1eeb8a59-c4ae-6bfc-8e56-010203040506 - counter: 3670! » cargo run Finished dev [unoptimized + debuginfo] target(s) in 0.01s Running `target/debug/weather` Hello from thread 1 - uuid: 1eeb8a59-e1dc-6918-8000-010203040506 - counter: 0! Hello from thread 2 - uuid: 1eeb8a59-e1dc-6af8-8002-010203040506 - counter: 2! Hello from thread 4 - uuid: 1eeb8a59-e1dc-6dbe-8003-010203040506 - counter: 3! Hello from thread 5 - uuid: 1eeb8a59-e1dc-6e2c-8004-010203040506 - counter: 4! Hello from thread 3 - uuid: 1eeb8a59-e1dc-6af8-8001-010203040506 - counter: 1! Hello from thread 6 - uuid: 1eeb8a59-e1dd-61ce-8005-010203040506 - counter: 5! Hello from thread 7 - uuid: 1eeb8a59-e1dd-625a-8006-010203040506 - counter: 6! Hello from thread 8 - uuid: 1eeb8a59-e1dd-6304-8007-010203040506 - counter: 7! Hello from thread 0 - uuid: 1eeb8a59-e1dd-6372-a008-010203040506 - counter: 8200! Hello from thread 9 - uuid: 1eeb8a59-e1dd-639a-a009-010203040506 - counter: 8201!Here are some runs from an Intel Core i7 (x86_64):
$ cargo run Finished dev [unoptimized + debuginfo] target(s) in 0.01s Running `target/debug/weather` Hello from thread 3 - uuid: 1eeb8a89-27dc-6f82-8000-010203040506 - counter: 0! Hello from thread 1 - uuid: 1eeb8a89-27dd-6060-8002-010203040506 - counter: 2! Hello from thread 0 - uuid: 1eeb8a89-27dc-6f81-8001-010203040506 - counter: 1! Hello from thread 4 - uuid: 1eeb8a89-27dd-66b4-8003-010203040506 - counter: 3! Hello from thread 5 - uuid: 1eeb8a89-27dd-6c9b-8004-010203040506 - counter: 4! Hello from thread 2 - uuid: 1eeb8a89-27de-604a-a68e-010203040506 - counter: 9870! Hello from thread 7 - uuid: 1eeb8a89-27de-61e2-a68f-010203040506 - counter: 9871! Hello from thread 6 - uuid: 1eeb8a89-27de-63e0-a690-010203040506 - counter: 9872! Hello from thread 8 - uuid: 1eeb8a89-27de-6485-a691-010203040506 - counter: 9873! Hello from thread 9 - uuid: 1eeb8a89-27de-674c-a692-010203040506 - counter: 9874! $ cargo run Finished dev [unoptimized + debuginfo] target(s) in 0.01s Running `target/debug/weather` Hello from thread 2 - uuid: 1eeb8a89-904f-6bd7-8001-010203040506 - counter: 1! Hello from thread 1 - uuid: 1eeb8a89-904f-6bd5-8000-010203040506 - counter: 0! Hello from thread 3 - uuid: 1eeb8a89-904f-6be2-8003-010203040506 - counter: 3! Hello from thread 4 - uuid: 1eeb8a89-904f-6bd5-8002-010203040506 - counter: 2! Hello from thread 5 - uuid: 1eeb8a89-9050-6809-8004-010203040506 - counter: 4! Hello from thread 0 - uuid: 1eeb8a89-9050-6b45-b4cd-010203040506 - counter: 13517! Hello from thread 6 - uuid: 1eeb8a89-9051-6243-b4ce-010203040506 - counter: 13518! Hello from thread 8 - uuid: 1eeb8a89-9051-648c-b4cf-010203040506 - counter: 13519! Hello from thread 7 - uuid: 1eeb8a89-9051-651d-b4d0-010203040506 - counter: 13520! Hello from thread 9 - uuid: 1eeb8a89-9051-67fa-b4d1-010203040506 - counter: 13521! $ cargo run Finished dev [unoptimized + debuginfo] target(s) in 0.01s Running `target/debug/weather` Hello from thread 1 - uuid: 1eeb8a89-ff0e-6a0d-8001-010203040506 - counter: 1! Hello from thread 2 - uuid: 1eeb8a89-ff0e-6a0d-8002-010203040506 - counter: 2! Hello from thread 3 - uuid: 1eeb8a89-ff0e-6a0b-8000-010203040506 - counter: 0! Hello from thread 4 - uuid: 1eeb8a89-ff0f-60ac-8003-010203040506 - counter: 3! Hello from thread 5 - uuid: 1eeb8a89-ff0f-65aa-8004-010203040506 - counter: 4! Hello from thread 0 - uuid: 1eeb8a89-ff0f-671d-9d90-010203040506 - counter: 7568! Hello from thread 6 - uuid: 1eeb8a89-ff0f-6999-9d91-010203040506 - counter: 7569! Hello from thread 9 - uuid: 1eeb8a89-ff0f-6cc4-9d92-010203040506 - counter: 7570! Hello from thread 7 - uuid: 1eeb8a89-ff0f-6ddf-9d93-010203040506 - counter: 7571! Hello from thread 8 - uuid: 1eeb8a89-ff0f-6fdb-9d94-010203040506 - counter: 7572!