Merge pull request #3139 from dumarchie/master

 Throw if keep/break is invoked on a vow more than once. Exception of type `X::Promise::IllegalTransition` would be thrown if `keep`/`break` are invoked on a vow taken on a promise that is not `Planned`.

This should resolve /issues/3137.

Note for Blin runs: this merge is likely to reveal a few vow misuses (i.e. repeated status change of a same `Promise`).

src/core.c/Channel.pm6

@@ -56,15 +56,13 @@ my class Channel does Awaitable {
           nqp::istype(msg,CHANNEL_CLOSE),
           nqp::stmts(
             nqp::push($!queue, msg),    # make sure other readers see it
-            $!closed_promise_vow.keep(Nil),
             X::Channel::ReceiveOnClosed.new(channel => self).throw
           ),
           nqp::if(
             nqp::istype(msg,CHANNEL_FAIL),
             nqp::stmts(
               nqp::push($!queue,msg),   # make sure other readers see it
-              $!closed_promise_vow.break(my $error := msg.error),
-              $error.rethrow
+              msg.error.rethrow
             ),
             nqp::stmts(
               self!peek(),              # trigger promise if closed
@@ -81,14 +79,12 @@ my class Channel does Awaitable {
           nqp::if(
             nqp::istype(msg, CHANNEL_CLOSE),
             nqp::stmts(
-              $!closed_promise_vow.keep(Nil),
               nqp::push($!queue, msg),
               Nil
             ),
             nqp::if(
               nqp::istype(msg, CHANNEL_FAIL),
               nqp::stmts(
-                $!closed_promise_vow.break(msg.error),
                 nqp::push($!queue, msg),
                 Nil
               ),
@@ -107,11 +103,11 @@ my class Channel does Awaitable {
             Nil
         } else {
             if nqp::istype(msg, CHANNEL_CLOSE) {
-                $!closed_promise_vow.keep(Nil);
+                try $!closed_promise_vow.keep(Nil);
                 Nil
             }
             elsif nqp::istype(msg, CHANNEL_FAIL) {
-                $!closed_promise_vow.break(msg.error);
+                try $!closed_promise_vow.break(msg.error);
                 Nil
             }
             else {
@@ -166,36 +162,42 @@ my class Channel does Awaitable {
         }
     }
 
+    my class Iterate { ... }
+    trusts Iterate;
     my class Iterate does Iterator {
         has $!queue;
-        has $!vow;
-        method !SET-SELF(\queue,\vow) {
+        has $!channel;
+        method !SET-SELF(\queue,\channel) {
             $!queue := queue;
-            $!vow := vow;
+            $!channel := channel;
             self
         }
-        method new(\queue,\vow) { nqp::create(self)!SET-SELF(queue,vow) }
+        method new(\queue,\channel) {
+            nqp::create(self)!SET-SELF(queue,channel);
+        }
         method pull-one() {
+            my \msg := nqp::shift($!queue);
             nqp::if(
-              nqp::istype((my \msg := nqp::shift($!queue)),CHANNEL_CLOSE),
+              nqp::istype(msg,CHANNEL_CLOSE),
               nqp::stmts(
                 nqp::push($!queue,msg),     # make sure other readers see it
-                $!vow.keep(Nil),
                 IterationEnd
               ),
               nqp::if(
                 nqp::istype(msg,CHANNEL_FAIL),
                 nqp::stmts(
                   nqp::push($!queue,msg),   # make sure other readers see it
-                  $!vow.break(my $error := msg.error),
-                  $error.rethrow
+                  msg.error.rethrow
                 ),
-                msg
+                nqp::stmts(
+                  $!channel!Channel::peek(),    # trigger promise if closed
+                  msg
+                )
               )
             )
         }
     }
-    method iterator(Channel:D:) { Iterate.new($!queue,$!closed_promise_vow) }
+    method iterator(Channel:D:) { Iterate.new($!queue,self) }
 
     method list(Channel:D:) { self.Seq.list }
 

src/core.c/IO/Socket/Async.pm6

@@ -166,7 +166,7 @@ my class IO::Socket::Async {
 
     method close(IO::Socket::Async:D: --> True) {
         nqp::closefh($!VMIO);
-        $!close-vow.keep(True);
+        try $!close-vow.keep(True);
     }
 
     method connect(IO::Socket::Async:U: Str() $host, Int() $port where Port-Number,

src/core.c/Promise.pm6

@@ -15,6 +15,12 @@ my class X::Promise::Vowed is Exception {
     has $.promise;
     method message() { "Access denied to keep/break this Promise; already vowed" }
 }
+my class X::Promise::Resolved is Exception {
+    has $.promise;
+    method message() {
+        "Cannot keep/break a Promise more than once (status: $!promise.status())";
+    }
+}
 my role X::Promise::Broken {
     has $.result-backtrace;
     multi method gist(::?CLASS:D:) {
@@ -96,6 +102,9 @@ my class Promise does Awaitable {
 
     method !keep(Mu \result --> Nil) {
         $!lock.protect({
+            X::Promise::Resolved.new(promise => self).throw
+             if $!status != Planned;
+
             $!result := result;
             $!status := Kept;
             self!schedule_thens();
@@ -125,6 +134,9 @@ my class Promise does Awaitable {
 
     method !break(\result --> Nil) {
         $!lock.protect({
+            X::Promise::Resolved.new(promise => self).throw
+             if $!status != Planned;
+
             $!result := nqp::istype(result, Exception)
                 ?? result
                 !! X::AdHoc.new(payload => result);