Terminate blocked receive packets on failure. Fixes #3168.

src/libcore/pipes.rs

@@ -396,6 +396,23 @@ fn try_recv<T: send, Tbuffer: send>(-p: recv_packet_buffered<T, Tbuffer>)
     let p_ = p.unwrap();
     let p = unsafe { &*p_ };
 
+    struct drop_state {
+        p: &packet_header;
+
+        drop {
+            if task::failing() {
+                io::println("failing!");
+                self.p.state = terminated;
+                let old_task = swap_task(self.p.blocked_task, ptr::null());
+                if !old_task.is_null() {
+                    rustrt::rust_task_deref(old_task);
+                }
+            }
+        }
+    };
+
+    let _drop_state = drop_state { p: &p.header };
+
     // optimistic path
     match p.header.state {
       full => {

src/test/run-pass/issue-3168.rs

+fn main() {
+    let (c,p) = pipes::stream();
+    do task::try {
+        let (c2,p2) = pipes::stream();
+        do task::spawn {
+            p2.recv();
+            #error["brother fails"];
+            fail;
+        }   
+        let (c3,p3) = pipes::stream();
+        c.send(c3);
+        c2.send(());
+        #error["child blocks"];
+        p3.recv();
+    };  
+    #error["parent tries"];
+    assert !p.recv().try_send(());
+    #error("all done!");
+}