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Auto merge of #10343 - asajeffrey:document-constellation-recv-panic, r=jdm

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Comment explaining constellation panic for recv

A retry of #10294, which was closed due to homu issues.

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This commit is contained in:
bors-servo 2016-04-02 23:08:45 +05:30
commit 85f9f9626e
1 changed files with 16 additions and 4 deletions
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20
components/compositing/constellation.rs
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@ -536,6 +536,17 @@ impl<LTF: LayoutThreadFactory, STF: ScriptThreadFactory> Constellation<LTF, STF>
Paint(FromPaintMsg)
}
// Get one incoming request.
// This is one of the few places where the compositor is
// allowed to panic. If one of the receiver.recv() calls
// fails, it is because the matching sender has been
// reclaimed, but this can't happen in normal execution
// because the constellation keeps a pointer to the sender,
// so it should never be reclaimed. A possible scenario in
// which receiver.recv() fails is if some unsafe code
// produces undefined behaviour, resulting in the destructor
// being called. If this happens, there's not much we can do
// other than panic.
let request = {
let receiver_from_script = &self.script_receiver;
let receiver_from_compositor = &self.compositor_receiver;
@ -543,16 +554,17 @@ impl<LTF: LayoutThreadFactory, STF: ScriptThreadFactory> Constellation<LTF, STF>
let receiver_from_paint = &self.painter_receiver;
select! {
msg = receiver_from_script.recv() =>
Request::Script(msg.unwrap()),
Request::Script(msg.expect("Unexpected script failure in constellation")),
msg = receiver_from_compositor.recv() =>
Request::Compositor(msg.unwrap()),
Request::Compositor(msg.expect("Unexpected compositor failure in constellation")),
msg = receiver_from_layout.recv() =>
Request::Layout(msg.unwrap()),
Request::Layout(msg.expect("Unexpected layout failure in constellation")),
msg = receiver_from_paint.recv() =>
Request::Paint(msg.unwrap())
Request::Paint(msg.expect("Unexpected paint failure in constellation"))
}
};
// Process the request.
match request {
// Messages from compositor