import tempfile
import pathlib
import threading
from concurrent.futures import ProcessPoolExecutor, ThreadPoolExecutor
from filelock import FileLock
import time

TEST_FILE = pathlib.Path(tempfile.gettempdir()) / 'test_file.txt'
TEST_LOCK_FILE =  pathlib.Path(tempfile.gettempdir()) / 'test_file.txt.lock'
LOCK = FileLock(TEST_LOCK_FILE)

def test():
    with LOCK:
        assert TEST_FILE.read_text() == 'hi'
        TEST_FILE.write_text('')
        assert TEST_FILE.read_text() == ''
        TEST_FILE.write_text('hi')
        assert TEST_FILE.read_text() == 'hi'
        return True

if __name__ == '__main__':
    print(f"Test file: {TEST_FILE}")
    print(f"Test lock file: {TEST_LOCK_FILE}")
    TEST_FILE.write_text('hi')

    results = []

    # works with ProcessPoolExecutor but not with ThreadPoolExecutor
    # It also is more likely to work if we sleep after calling submit()
    with ThreadPoolExecutor(max_workers=16) as pool:
        for i in range(100):
            if i % 10 == 0:
                print (f"Loop: {i+1}")
            results.append(pool.submit(test))

        for idx, result in enumerate(results):
            print (f"Checking result: {idx + 1}")
            assert result.result() == True

PS C:\Users\csm10495\Desktop> python .\file_lock_test.py
Test file: C:\Users\csm10495\AppData\Local\Temp\test_file.txt
Test lock file: C:\Users\csm10495\AppData\Local\Temp\test_file.txt.lock
Loop: 1
Loop: 11
Loop: 21
Loop: 31
Loop: 41
Loop: 51
Loop: 61
Loop: 71
Loop: 81
Loop: 91
Checking result: 1
Traceback (most recent call last):
  File ".\file_lock_test.py", line 38, in <module>
    assert result.result() == True
  File "C:\Python37\lib\concurrent\futures\_base.py", line 425, in result
    return self.__get_result()
  File "C:\Python37\lib\concurrent\futures\_base.py", line 384, in __get_result
    raise self._exception
  File "C:\Python37\lib\concurrent\futures\thread.py", line 57, in run
    result = self.fn(*self.args, **self.kwargs)
  File ".\file_lock_test.py", line 18, in test
    assert TEST_FILE.read_text() == 'hi'
AssertionError