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Daniil Gentili 2023-08-27 22:06:08 +02:00
parent 75171c136d
commit 352a73767d
Signed by: danog
GPG Key ID: 8C1BE3B34B230CA7
2 changed files with 35 additions and 0 deletions
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17
src/borrow_unchecked.rs
View File

@ -1,5 +1,22 @@
// Borrowed from https://github.com/jeremyBanks/you-can // Borrowed from https://github.com/jeremyBanks/you-can
// What's going on here? Unsafe borrows???
// NO: this is actually 100% safe, and here's why.
//
// This is needed because of https://github.com/danog/php-tokio/blob/master/src/event_loop.rs#L72
//
// Rust thinks we're Sending the Future to another thread (tokio's event loop),
// where it may be used even after its lifetime expires in the main (PHP) thread.
//
// In reality, the Future is only used by Tokio until the result is ready.
//
// Rust does not understand that when we suspend the current fiber in suspend_on,
// we basically keep alive the the entire stack,
// including the Rust stack and the Future on it, until the result of the future is ready.
//
// Once the result of the Future is ready, tokio doesn't need it anymore,
// the suspend_on function is resumed, and we safely drop the Future upon exiting.
use nicelocal_ext_php_rs::binary_slice::{BinarySlice, PackSlice}; use nicelocal_ext_php_rs::binary_slice::{BinarySlice, PackSlice};

18
src/event_loop.rs
View File

@ -61,6 +61,21 @@ impl EventLoop {
} }
pub fn suspend_on<T: Send + 'static, F: Future<Output = T> + Send + 'static>(future: F) -> T { pub fn suspend_on<T: Send + 'static, F: Future<Output = T> + Send + 'static>(future: F) -> T {
// What's going on here? Unsafe borrows???
// NO: this is actually 100% safe, and here's why.
//
// Rust thinks we're Sending the Future to another thread (tokio's event loop),
// where it may be used even after its lifetime expires in the main (PHP) thread.
//
// In reality, the Future is only used by Tokio until the result is ready.
//
// Rust does not understand that when we suspend the current fiber in suspend_on,
// we basically keep alive the the entire stack,
// including the Rust stack and the Future on it, until the result of the future is ready.
//
// Once the result of the Future is ready, tokio doesn't need it anymore,
// the suspend_on function is resumed, and we safely drop the Future upon exiting.
//
let (future, get_current_suspension) = EVENTLOOP.with_borrow_mut(move |c| { let (future, get_current_suspension) = EVENTLOOP.with_borrow_mut(move |c| {
let c = c.as_mut().unwrap(); let c = c.as_mut().unwrap();
let idx = c.fibers.len() as u64; let idx = c.fibers.len() as u64;
@ -79,8 +94,11 @@ impl EventLoop {
}) })
}); });
// We suspend the fiber here, the Rust stack is kept alive until the result is ready.
call_user_func!(get_current_suspension).unwrap().try_call_method("suspend", vec![]).unwrap(); call_user_func!(get_current_suspension).unwrap().try_call_method("suspend", vec![]).unwrap();
// We've resumed, the `future` is already resolved and is not used by the tokio thread, it's safe to drop it.
return RUNTIME.block_on(future).unwrap(); return RUNTIME.block_on(future).unwrap();
} }