fixes #4776

tests/parallel/tsendtwice.nim

@@ -0,0 +1,71 @@
+discard """
+  output: '''obj2 nil
+obj nil
+obj3 nil
+3
+obj2 nil
+obj nil
+obj3 nil'''
+  cmd: "nim c -r --threads:on $file"
+"""
+
+# bug #4776
+
+import tables
+
+type
+  Base* = ref object of RootObj
+    someSeq: seq[int]
+    baseData: array[400000, byte]
+  Derived* = ref object of Base
+    data: array[400000, byte]
+
+type
+  ThreadPool = ref object
+    threads: seq[ptr Thread[ThreadArg]]
+    channels: seq[ThreadArg]
+  TableChannel = Channel[TableRef[string, Base]]
+  ThreadArg = ptr TableChannel
+
+var globalTable {.threadvar.}: TableRef[string, Base]
+globalTable = newTable[string, Base]()
+let d = new(Derived)
+globalTable.add("obj", d)
+globalTable.add("obj2", d)
+globalTable.add("obj3", d)
+
+proc testThread(channel: ptr TableChannel) {.thread.} =
+  globalTable = channel[].recv()
+  for k, v in pairs globaltable:
+    echo k, " ", v.someSeq
+  var myObj: Base
+  deepCopy(myObj, globalTable["obj"])
+  myObj.someSeq = newSeq[int](100)
+  let table = channel[].recv() # same table
+  echo table.len
+  for k, v in mpairs table:
+    echo k, " ", v.someSeq
+  assert(table.contains("obj")) # fails!
+  assert(table.contains("obj2")) # fails!
+  assert(table.contains("obj3")) # fails!
+
+var channel: TableChannel
+
+proc newThreadPool(threadCount: int) = #: ThreadPool =
+  #new(result)
+  #result.threads = newSeq[ptr Thread[ThreadArg]](threadCount)
+  #var channel = cast[ptr TableChannel](allocShared0(sizeof(TableChannel)))
+  channel.open()
+  channel.send(globalTable)
+  channel.send(globalTable)
+  #createThread(threadPtr[], testThread, addr channel)
+  testThread(addr channel)
+  #result.threads[i] = threadPtr
+
+proc stop(p: ThreadPool) =
+  for t in p.threads:
+    joinThread(t[])
+    dealloc(t)
+
+
+newThreadPool(1)#.stop()