fix use-after-free in test (detected in win32 CI)

Author: vtjnash

test/threads.jl

@@ -415,8 +415,8 @@ let e = Base.Event(true),
     newthreads = zeros(Int16, length(tids))
     onces = Vector{Vector{Nothing}}(undef, length(tids))
     allonces = Vector{Vector{Vector{Nothing}}}(undef, length(tids))
-    for i = 1:length(tids)
-        function cl()
+    # allocate closure memory to last until all threads are started
+    cls = [function cl()
             GC.gc(false) # stress test the GC-safepoint mechanics of jl_adopt_thread
             try
                 newthreads[i] = threadid()
@@ -434,43 +434,50 @@ let e = Base.Event(true),
             GC.gc(false) # stress test the GC-safepoint mechanics of jl_delete_thread
             nothing
         end
-        function threadcallclosure(cl::F) where {F} # create sparam so we can reference the type of cl in the ccall type
-            threadwork = @cfunction cl -> cl() Cvoid (Ref{F},) # create a cfunction that specializes on cl as an argument and calls it
-            err = @ccall uv_thread_create(Ref(tids, i)::Ptr{UInt}, threadwork::Ptr{Cvoid}, cl::Ref{F})::Cint # call that on a thread
-            err == 0 || Base.uv_error("uv_thread_create", err)
-        end
-        threadcallclosure(cl)
-    end
-    @noinline function waitallthreads(tids)
+    for i = 1:length(tids)]
+    GC.@preserve cls begin # this memory must survive until each corresponding thread exits (waitallthreads / uv_thread_join)
+        Base.preserve_handle(cls)
         for i = 1:length(tids)
-            tid = Ref(tids, i)
-            tidp = Base.unsafe_convert(Ptr{UInt}, tid)::Ptr{UInt}
-            gc_state = @ccall jl_gc_safe_enter()::Int8
-            GC.@preserve tid err = @ccall uv_thread_join(tidp::Ptr{UInt})::Cint
-            @ccall jl_gc_safe_leave(gc_state::Int8)::Cvoid
-            err == 0 || Base.uv_error("uv_thread_join", err)
-        end
-    end
-    try
-        # let them finish in batches of 10
-        for i = 1:length(tids) ÷ 10
-            for i = 1:10
-                newid = take!(started)
-                @test newid != threadid()
+            function threadcallclosure(tid::Ref{UInt}, cl::Ref{F}) where {F} # create sparam so we can reference the type of cl in the ccall type
+                threadwork = @cfunction cl -> cl() Cvoid (Ref{F},) # create a cfunction that specializes on cl as an argument and calls it
+                err = @ccall uv_thread_create(tid::Ptr{UInt}, threadwork::Ptr{Cvoid}, cl::Ref{F})::Cint # call that on a thread
+                err == 0 || Base.uv_error("uv_thread_create", err)
+                nothing
             end
-            for i = 1:10
-                push!(finish, nothing)
+            threadcallclosure(Ref(tids, i), Ref(cls, i))
+        end
+        @noinline function waitallthreads(tids, cls)
+            for i = 1:length(tids)
+                tid = Ref(tids, i)
+                tidp = Base.unsafe_convert(Ptr{UInt}, tid)::Ptr{UInt}
+                gc_state = @ccall jl_gc_safe_enter()::Int8
+                GC.@preserve tid err = @ccall uv_thread_join(tidp::Ptr{UInt})::Cint
+                @ccall jl_gc_safe_leave(gc_state::Int8)::Cvoid
+                err == 0 || Base.uv_error("uv_thread_join", err)
             end
+            Base.unpreserve_handle(cls)
         end
-        @test isempty(started)
-        # now run the second part of the test where they all try to access the other threads elements
-        notify(starttest2)
-    finally
-        for _ = 1:length(tids)
-            # run IO loop until all threads are close to exiting
-            take!(exiting)
+        try
+            # let them finish in batches of 10
+            for i = 1:length(tids) ÷ 10
+                for i = 1:10
+                    newid = take!(started)
+                    @test newid != threadid()
+                end
+                for i = 1:10
+                    push!(finish, nothing)
+                end
+            end
+            @test isempty(started)
+            # now run the second part of the test where they all try to access the other threads elements
+            notify(starttest2)
+        finally
+            for _ = 1:length(tids)
+                # run IO loop until all threads are close to exiting
+                take!(exiting)
+            end
+            waitallthreads(tids, cls)
         end
-        waitallthreads(tids)
     end
     @test isempty(started)
     @test isempty(finish)