contrib.concurrent.process_map: fix threading.RLock pickling error

- fixes #920

tqdm/contrib/concurrent.py

@@ -35,6 +35,7 @@ def _executor_map(PoolExecutor, fn, *iterables, **tqdm_kwargs):
     tqdm_class  : [default: tqdm.auto.tqdm].
     max_workers  : [default: min(32, cpu_count() + 4)].
     chunksize  : [default: 1].
+    lock_name  : [default: "":str].
     """
     kwargs = tqdm_kwargs.copy()
     if "total" not in kwargs:
@@ -42,12 +43,14 @@ def _executor_map(PoolExecutor, fn, *iterables, **tqdm_kwargs):
     tqdm_class = kwargs.pop("tqdm_class", tqdm_auto)
     max_workers = kwargs.pop("max_workers", min(32, cpu_count() + 4))
     chunksize = kwargs.pop("chunksize", 1)
+    lock_name = kwargs.pop("lock_name", "")
     pool_kwargs = dict(max_workers=max_workers)
     sys_version = sys.version_info[:2]
     if sys_version >= (3, 7):
         # share lock in case workers are already using `tqdm`
-        pool_kwargs.update(
-            initializer=tqdm_class.set_lock, initargs=(tqdm_class.get_lock(),))
+        lock = tqdm_class.get_lock()
+        lock = getattr(lock, lock_name, lock)
+        pool_kwargs.update(initializer=tqdm_class.set_lock, initargs=(lock,))
     map_args = {}
     if not (3, 0) < sys_version < (3, 5):
         map_args.update(chunksize=chunksize)
@@ -90,6 +93,8 @@ def process_map(fn, *iterables, **tqdm_kwargs):
     chunksize : int, optional
         Size of chunks sent to worker processes; passed to
         `concurrent.futures.ProcessPoolExecutor.map`. [default: 1].
+    lock_name  : str, optional
+        Member of `tqdm_class.get_lock()` to use [default: mp_lock].
     """
     from concurrent.futures import ProcessPoolExecutor
     if iterables and "chunksize" not in tqdm_kwargs:
@@ -102,4 +107,7 @@ def process_map(fn, *iterables, **tqdm_kwargs):
                  " This may seriously degrade multiprocess performance."
                  " Set `chunksize=1` or more." % longest_iterable_len,
                  TqdmWarning, stacklevel=2)
+    if "lock_name" not in tqdm_kwargs:
+        tqdm_kwargs = tqdm_kwargs.copy()
+        tqdm_kwargs["lock_name"] = "mp_lock"
     return _executor_map(ProcessPoolExecutor, fn, *iterables, **tqdm_kwargs)