Reduce readers in test_racing_join_replace to 10, use Event to synchr…

…onize, and perform multiple joins per loop to increase chance of repro without synchronization

Lib/test/test_free_threading/test_str.py

@@ -42,20 +42,21 @@ def test_racing_join_replace(self):
  '''
  l = [*'abcdefg']
  MAX_ORDINAL = 1_000
- READERS = 20
+ READERS = 10
+ done_event = Event()
 
  def writer_func():
  for i, c in zip(cycle(range(len(l))),
  map(chr, range(128, MAX_ORDINAL))):
  l[i] = c
- del l[:] # Empty list to tell readers to exit
+ done_event.set()
 
  def reader_func():
- while True:
- empty = not l
+ while not done_event.is_set():
+ ''.join(l)
+ ''.join(l)
+ ''.join(l)
  ''.join(l)
- if empty:
- break
 
  writer = Thread(target=writer_func)
  readers = []