Fix number of tune steps with cores>1

pymc3/parallel_sampling.py

@@ -110,7 +110,7 @@ class _Process(multiprocessing.Process):
     and send finished samples using shared memory.
     """
 
-    def __init__(self, name, msg_pipe, step_method, shared_point, draws, tune, seed):
+    def __init__(self, name:str, msg_pipe, step_method, shared_point, draws:int, tune:int, seed):
         super().__init__(daemon=True, name=name)
         self._msg_pipe = msg_pipe
         self._step_method = step_method
@@ -173,6 +173,10 @@ def _start_loop(self):
             raise ValueError("Unexpected msg " + msg[0])
 
         while True:
+            if draw == self._tune:
+                self._step_method.stop_tuning()
+                tuning = False
+
             if draw < self._draws + self._tune:
                 try:
                     point, stats = self._compute_point()
@@ -183,10 +187,6 @@ def _start_loop(self):
             else:
                 return
 
-            if draw == self._tune:
-                self._step_method.stop_tuning()
-                tuning = False
-
             msg = self._recv_msg()
             if msg[0] == "abort":
                 raise KeyboardInterrupt()
@@ -222,7 +222,7 @@ def _collect_warnings(self):
 class ProcessAdapter:
     """Control a Chain process from the main thread."""
 
-    def __init__(self, draws, tune, step_method, chain, seed, start):
+    def __init__(self, draws:int, tune:int, step_method, chain:int, seed, start):
         self.chain = chain
         process_name = "worker_chain_%s" % chain
         self._msg_pipe, remote_conn = multiprocessing.Pipe()
@@ -353,15 +353,15 @@ def terminate_all(processes, patience=2):
 class ParallelSampler:
     def __init__(
         self,
-        draws,
-        tune,
-        chains,
-        cores,
-        seeds,
-        start_points,
+        draws:int,
+        tune:int,
+        chains:int,
+        cores:int,
+        seeds:list,
+        start_points:list,
         step_method,
-        start_chain_num=0,
-        progressbar=True,
+        start_chain_num:int=0,
+        progressbar:bool=True,
     ):
 
         if any(len(arg) != chains for arg in [seeds, start_points]):

pymc3/tests/test_sampling.py

@@ -127,6 +127,18 @@ def test_sample_tune_len(self):
             trace = pm.sample(draws=100, tune=50, cores=4)
             assert len(trace) == 100
 
+    @pytest.mark.parametrize('cores', [1, 2])
+    def test_sampler_stat_tune(self, cores):
+        with self.model:
+            tune_stat = pm.sample(
+                tune=5, draws=7, cores=cores,
+                discard_tuned_samples=False,
+                step=pm.Metropolis()
+            ).get_sampler_stats('tune', chains=1)
+            assert list(tune_stat).count(True) == 5
+            assert list(tune_stat).count(False) == 7
+        pass
+
     @pytest.mark.parametrize(
         "start, error",
         [