shim Apple's futex primitives #4142
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This is necessary to unblock rust-lang/rust#122408. The documentation for these is available [here](https://developer.apple.com/documentation/os/os_sync_wait_on_address?language=objc). Because the futex wait operations (`os_sync_wait_on_address` et al.) return the number of remaining waiters after returning, this required some changes to the common futex infrastructure, which I've changed to take a callback instead of precalculating the return values.
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Thanks for the PR! I just left for a 1-week business trip and will have to catch up with stuff when I am back so it could take a bit before I can take a closer look. |
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☔ The latest upstream changes (possibly 489a487) made this pull request unmergeable. Please resolve the merge conflicts. |
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S-waiting-on-author
| /// * On a signal, `retval_succ` is called with the number of waiters on the | ||
| /// futex and its result is written to `dest`. | ||
| /// * On a timeout, `retval_timeout` is written to `dest` and `errno_timeout` | ||
| /// is set as the last error. |
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Most of the variables referenced here do not exist any more.
| } | ||
| |ecx, unblock: UnblockKind| match unblock { | ||
| UnblockKind::Ready => { | ||
| ecx.write_scalar(Scalar::from_target_isize(0, ecx), &dest) |
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| ecx.write_scalar(Scalar::from_target_isize(0, ecx), &dest) | |
| ecx.write_int(0, &dest) |
| |this, unblock: UnblockKind| { | ||
| match unblock { | ||
| UnblockKind::Ready => { | ||
| this.write_scalar(Scalar::from_i32(1), &dest) |
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| this.write_scalar(Scalar::from_i32(1), &dest) | |
| this.write_int(1, &dest) |
| } | ||
| UnblockKind::TimedOut => { | ||
| this.set_last_error(IoError::WindowsError("ERROR_TIMEOUT"))?; | ||
| this.write_scalar(Scalar::from_i32(0), &dest) |
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| this.write_scalar(Scalar::from_i32(0), &dest) | |
| this.write_int(0, &dest) |
| @@ -216,6 +224,53 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> { | |||
| this.write_scalar(res, dest)?; | |||
| } | |||
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| "os_sync_wait_on_address" => { | |||
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| "os_sync_wait_on_address" => { | |
| // Futex primitives | |
| "os_sync_wait_on_address" => { |
| fn wake_nobody() { | ||
| let futex = 0; | ||
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| // Wake 1 waiter. Expect zero waiters woken up, as nobody is waiting. |
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| // Wake 1 waiter. Expect zero waiters woken up, as nobody is waiting. | |
| // Wake 1 waiter. Expect ENOENT, as nobody is waiting. |
| ), | ||
| -1 | ||
| ); | ||
| assert_eq!(io::Error::last_os_error().raw_os_error().unwrap(), libc::ENOENT); |
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So this is the same error as "nobody is waiting"? Interesting.
| // Add 200ms (note: this only works under miri because it uses nanosecond units for | ||
| // mach_absolute_time). | ||
| deadline += 200_000_000; |
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This sounds like we are doing something wrong, then?
| t.join().unwrap(); | ||
| } | ||
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| fn param_mismatch() { |
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Please add comments pointing out what the mismatch is in each case.
| size_of::<i32>(), | ||
| libc::OS_SYNC_WAIT_ON_ADDRESS_NONE, | ||
| ), | ||
| 0, |
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Please add a test where wait_on_address returns something non-zero (since there are more waiters).
This is necessary to unblock rust-lang/rust#122408. The documentation for these is available here.
Because the futex wait operations (
os_sync_wait_on_addresset al.) return the number of remaining waiters after returning, this required some changes to the common futex infrastructure, which I've changed to take a callback instead of precalculating the return values.