Fixes #4719. (#5585)

tests/threads/tmanyjoin.nim

@@ -0,0 +1,30 @@
+discard """
+  outputsub: "129"
+"""
+
+import os, locks
+
+type
+  MarkerObj = object
+    lock: Lock
+    counter: int
+  Marker = ptr MarkerObj
+
+const
+  ThreadsCount = 129
+  SleepTime = 1000
+
+proc worker(p: Marker) {.thread.} =
+  acquire(p.lock)
+  inc(p.counter)
+  release(p.lock)
+  sleep(SleepTime)
+
+var p = cast[Marker](allocShared0(sizeof(MarkerObj)))
+initLock(p.lock)
+var ts = newSeq[Thread[Marker]](ThreadsCount)
+for i in 0..<ts.len:
+  createThread(ts[i], worker, p)
+
+joinThreads(ts)
+echo p.counter

tests/threads/treusetvar.nim

@@ -0,0 +1,28 @@
+discard """
+  outputsub: "129"
+"""
+
+import os, locks
+
+type
+  MarkerObj = object
+    lock: Lock
+    counter: int
+  Marker = ptr MarkerObj
+
+const
+  ThreadsCount = 129
+
+proc worker(p: Marker) {.thread.} =
+  acquire(p.lock)
+  inc(p.counter)
+  release(p.lock)
+
+var p = cast[Marker](allocShared0(sizeof(MarkerObj)))
+initLock(p.lock)
+
+for i in 0..(ThreadsCount - 1):
+  var thread: Thread[Marker]
+  createThread(thread, worker, p)
+  joinThread(thread)
+echo p.counter