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Fixed borrowck problems with nu_select! in an evil way

This commit is contained in:
Andrew Poelstra 2014-07-26 11:28:55 -07:00
parent b5b7a6b080
commit 322c937c3c
1 changed files with 14 additions and 5 deletions
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19
src/macros.rs
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@ -28,6 +28,15 @@ macro_rules! nu_select(
use rustrt::task::Task;
use sync::comm::Packet;
/// Obtains a borrowed reference to an object for an arbitrary amount of
/// time (it is on you to make sure the aliasing rules are followed and
/// that the borrow does not exceed the object's lifetime!!!!!!!!!!!!!!)
/// to subvert the borrow-checker. This is a workaround for the current
/// lexical-scope-based borrow times.
unsafe fn borrow_without_checking<'a, 'b, T>(obj: &'a T) -> &'b T {
&*(obj as *const _)
}
// Is anything already ready to receive? Grab it without waiting.
$(
if (&$rx as &Packet).can_recv() {
@ -41,7 +50,8 @@ macro_rules! nu_select(
// Keep count of how many, since we need to abort every selection
// that we started.
let mut started_count = 0;
let packets = [ $( &$rx as &Packet, )+ ];
// Restrict lifetime of borrows in `packets`
let packets = [ $( unsafe { borrow_without_checking(&$rx) } as &Packet, )+ ];
let task: Box<Task> = Local::take();
task.deschedule(packets.len(), |task| {
@ -59,9 +69,7 @@ macro_rules! nu_select(
// Abort every one, but only react to the first
if { i += 1; i < started_count } &&
// If start_selection() failed, abort_selection() will fail too,
// but it still counts as "data available". FIXME: should we swap
// the following two conditions so that packets[started_count - 1].
// abort_selection() is never called?
// but it still counts as "data available".
(packets[i].abort_selection() || i == started_count - 1) {
// Abort the remainder, ignoring their return values
i += 1;
@ -69,13 +77,14 @@ macro_rules! nu_select(
packets[i].abort_selection();
i += 1;
}
// End manually-tracked borrow of $rx in packets
drop(packets);
// React to the first
let $name = $rx.$meth();
$code
}
)else+
else {
println!("i = {} , started_count {}", i, started_count);
fail!("we didn't find the ready receiver, but we should have had one"); }
}
})