fix serialization of multiple global bindings to the same object in a…

… closure (JuliaLang#21700)

* fix serialization of multiple global bindings to the same object in a closure

base/distributed/clusterserialize.jl

@@ -114,7 +114,7 @@ function syms_2b_sent(s::ClusterSerializer, identifier)
  oid = object_id(v)
  if haskey(s.glbs_sent, oid)
  # We have sent this object before, see if it has changed.
- s.glbs_sent[oid] != hash(v) && push!(lst, sym)
+ s.glbs_sent[oid] != hash(sym, hash(v)) && push!(lst, sym)
  else
  push!(lst, sym)
  end
@@ -143,7 +143,7 @@ function serialize_global_from_main(s::ClusterSerializer, sym)
  end
  end
  end
- record_v && (s.glbs_sent[oid] = hash(v))
+ record_v && (s.glbs_sent[oid] = hash(sym, hash(v)))
 
  serialize(s, isconst(Main, sym))
  serialize(s, v)

test/distributed_exec.jl

@@ -1358,6 +1358,13 @@ for i in 1:5
  @test remotecall_fetch(()->v2, id_other) == v2
 end
 
+# Different global bindings to the same object
+global v3 = ones(10)
+global v4 = v3
+@test remotecall_fetch(()->v3, id_other) == remotecall_fetch(()->v4, id_other)
+@test remotecall_fetch(()->isdefined(Main, :v3), id_other)
+@test remotecall_fetch(()->isdefined(Main, :v4), id_other)
+
 # Test that a global is not being repeatedly serialized when
 # a) referenced multiple times in the closure
 # b) hash value has not changed.