Fix issue 31252 - remote globals not being updated in some cases

stdlib/Distributed/src/clusterserialize.jl

@@ -15,7 +15,7 @@ mutable struct ClusterSerializer{I<:IO} <: AbstractSerializer
 
     pid::Int                                     # Worker we are connected to.
     tn_obj_sent::Set{UInt64}                     # TypeName objects sent
-    glbs_sent::Dict{UInt64, UInt64}              # (key,value) -> (objectid, hash_value)
+    glbs_sent::Dict{Symbol, Tuple{UInt64, UInt64}}   # (key,value) -> (symbol, (hash_value, objectid))
     glbs_in_tnobj::Dict{UInt64, Vector{Symbol}}  # Track globals referenced in
                                                  # anonymous functions.
     anonfunc_id::UInt64
@@ -116,10 +116,11 @@ function serialize(s::ClusterSerializer, g::GlobalRef)
     invoke(serialize, Tuple{AbstractSerializer, GlobalRef}, s, g)
 end
 
-# Send/resend a global object if
-# a) has not been sent previously, i.e., we are seeing this objectid for the first time, or,
+# Send/resend a global binding if
+# a) has not been sent previously, i.e., we are seeing this binding for the first time, or,
 # b) hash value has changed or
-# c) is a bits type
+# c) hash value is same but of a different object, i.e. objectid has changed or
+# d) is a bits type
 function syms_2b_sent(s::ClusterSerializer, identifier)
     lst = Symbol[]
     check_syms = get(s.glbs_in_tnobj, identifier, [])
@@ -129,10 +130,12 @@ function syms_2b_sent(s::ClusterSerializer, identifier)
         if isbits(v)
             push!(lst, sym)
         else
-            oid = objectid(v)
-            if haskey(s.glbs_sent, oid)
-                # We have sent this object before, see if it has changed.
-                s.glbs_sent[oid] != hash(sym, hash(v)) && push!(lst, sym)
+            if haskey(s.glbs_sent, sym)
+                # We have sent this binding before, see if it has changed.
+                hval, oid = s.glbs_sent[sym]
+                if hval != hash(sym, hash(v)) || oid != objectid(v)
+                    push!(lst, sym)
+                end
             else
                 push!(lst, sym)
             end
@@ -144,26 +147,9 @@ end
 function serialize_global_from_main(s::ClusterSerializer, sym)
     v = getfield(Main, sym)
 
-    oid = objectid(v)
-    record_v = true
-    if isbits(v)
-        record_v = false
-    elseif !haskey(s.glbs_sent, oid)
-        # set up a finalizer the first time this object is sent
-        try
-            finalizer(v) do x
-                delete_global_tracker(s,x)
-            end
-        catch ex
-            # Do not track objects that cannot be finalized.
-            if isa(ex, ErrorException)
-                record_v = false
-            else
-                rethrow()
-            end
-        end
+    if !isbits(v)
+        s.glbs_sent[sym] = (hash(sym, hash(v)), objectid(v))
     end
-    record_v && (s.glbs_sent[oid] = hash(sym, hash(v)))
 
     serialize(s, isconst(Main, sym))
     serialize(s, v)
@@ -180,17 +166,6 @@ function deserialize_global_from_main(s::ClusterSerializer, sym)
     return nothing
 end
 
-function delete_global_tracker(s::ClusterSerializer, v)
-    oid = objectid(v)
-    if haskey(s.glbs_sent, oid)
-        delete!(s.glbs_sent, oid)
-    end
-
-    # TODO: A global binding is released and gc'ed here but it continues
-    # to occupy memory on the remote node. Would be nice to release memory
-    # if possible.
-end
-
 function cleanup_tname_glbs(s::ClusterSerializer, identifier)
     delete!(s.glbs_in_tnobj, identifier)
 end

stdlib/Distributed/test/distributed_exec.jl

@@ -1214,6 +1214,29 @@ v6 = FooModEverywhere
 @test remotecall_fetch(()->v5, id_other) === FooStructEverywhere
 @test remotecall_fetch(()->v6, id_other) === FooModEverywhere
 
+# hash value same but different object instance
+v7 = ones(10)
+oid1 = objectid(v7)
+hval1 = hash(v7)
+@test v7 == @fetchfrom id_other v7
+remote_oid1 = @fetchfrom id_other objectid(v7)
+
+v7 = ones(10)
+@test oid1 != objectid(v7)
+@test hval1 == hash(v7)
+@test remote_oid1 != @fetchfrom id_other objectid(v7)
+
+
+# Github issue #31252
+v31252 = :a
+@test :a == @fetchfrom id_other v31252
+
+v31252 = :b
+@test :b == @fetchfrom id_other v31252
+
+v31252 = :a
+@test :a == @fetchfrom id_other v31252
+
 
 # Test that a global is not being repeatedly serialized when
 # a) referenced multiple times in the closure
@@ -1311,10 +1334,6 @@ global ids_func = ()->ids_cleanup
 clust_ser = (Distributed.worker_from_id(id_other)).w_serializer
 @test remotecall_fetch(ids_func, id_other) == ids_cleanup
 
-@test haskey(clust_ser.glbs_sent, objectid(ids_cleanup))
-finalize(ids_cleanup)
-@test !haskey(clust_ser.glbs_sent, objectid(ids_cleanup))
-
 # TODO Add test for cleanup from `clust_ser.glbs_in_tnobj`
 
 # reported github issues - Mostly tests with globals and various distributed macros