bugfix: leaked semaphore error (#309)

* use config for n_cpu

* rm import

* fix process loop

* unuse mp.spawn

ref. https://discuss.pytorch.org/t/how-to-fix-a-sigsegv-in-pytorch-when-using-distributed-training-e-g-ddp/113518/10

* fix commentout

extract_f0_print.py

@@ -154,7 +154,7 @@ if __name__ == "__main__":
                 f0method,
             ),
         )
-        p.start()
         ps.append(p)
-    for p in ps:
-        p.join()
+        p.start()
+    for i in range(n_p):
+        ps[i].join()