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// program inspired by "Proving Copyless Message Passing" (Villard, Lozes and Calcagno, APLAS 2009)
// msg tag indicates what the type of the message
// channel is freed by Getter when it completes
// todo: accept ack message before sending the next one (requires sending negative credit!)
channel C(msg: bool, n: Node) where n!= null && acc(n.next) && acc(n.mu) && (msg ==> credit(this, 1)) && (!msg ==> acc(this.mu, 50));
class Node {
var next: Node;
function length(): int
requires this.list;
{
unfolding this.list in 1 + (next == null ? 0 : next.length())
}
predicate list {
acc(next) && acc(mu) && (next != null ==> next.list)
}
}
class Program {
method Putter(e: C, x0: Node)
requires e!= null && acc(e.mu, 50) && (x0 != null ==> x0.list) && (x0 != null ==> credit(e, - 1));
{
var x: Node := x0;
var t: Node;
while(x != null)
invariant (x != null ==> x.list) && (x!=null ==> acc(e.mu, 50)) && (x != null ==> credit(e, - 1));
{
unfold x.list;
t := x.next;
if(t != null) {
send e(true, x);
} else {
send e(false, x);
}
x := t;
}
}
method Getter(f: C)
requires f!= null && credit(f, 1) && acc(f.mu, 50) && waitlevel << f.mu;
{
var x: Node := null;
var msg: bool := true;
while(msg)
invariant acc(f.mu, 50) && waitlevel << f.mu && (msg ==> credit(f, 1)) && (!msg ==> acc(f.mu, 50));
{
receive msg, x := f;
if(msg) {
free x;
}
}
free f; // close the channel
}
method Main(x: Node)
requires x != null;
requires x.list;
{
var e := new C;
fork Putter(e, x);
fork Getter(e);
}
}
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