Prevent potential errors with the SF process, and misc.

README.md

@@ -25,7 +25,7 @@ You should install the stockfish engine in your operating system globally or spe
 ```python
 from stockfish import Stockfish
 
-stockfish = Stockfish("/Users/zhelyabuzhsky/Work/stockfish/stockfish-9-64")
+stockfish = Stockfish(path="/Users/zhelyabuzhsky/Work/stockfish/stockfish-9-64")
 ```
 
 There are some default engine's settings:
@@ -46,9 +46,9 @@ There are some default engine's settings:
 }
 ```
 
-You can change them during your Stockfish class initialization:
+You can change them, as well as the default search depth, during your Stockfish class initialization:
 ```python
-stockfish = Stockfish(parameters={"Threads": 2, "Minimum Thinking Time": 30})
+stockfish = Stockfish(path="/Users/zhelyabuzhsky/Work/stockfish/stockfish-9-64", depth=18, parameters={"Threads": 2, "Minimum Thinking Time": 30})
 ```
 
 ### Set position by sequence of moves

stockfish/models.py

@@ -16,7 +16,7 @@ class Stockfish:
     """Integrates the Stockfish chess engine with Python."""
 
     def __init__(
-        self, path: str = "stockfish", depth: int = 2, parameters: dict = None
+        self, path: str = "stockfish", depth: int = 15, parameters: dict = None
     ) -> None:
         self.default_stockfish_params = {
             "Write Debug Log": "false",
@@ -35,14 +35,16 @@ def __init__(
             "UCI_Elo": 1350,
             "UCI_ShowWDL": "false",
         }
-        self.stockfish = subprocess.Popen(
+        self._stockfish = subprocess.Popen(
             path,
             universal_newlines=True,
             stdin=subprocess.PIPE,
             stdout=subprocess.PIPE,
             stderr=subprocess.STDOUT,
         )
 
+        self._has_quit_command_been_sent = False
+
         self._stockfish_major_version: int = int(
             self._read_line().split(" ")[1].split(".")[0]
         )
@@ -93,15 +95,18 @@ def _prepare_for_new_position(self, send_ucinewgame_token: bool = True) -> None:
         self.info = ""
 
     def _put(self, command: str) -> None:
-        if not self.stockfish.stdin:
+        if not self._stockfish.stdin:
             raise BrokenPipeError()
-        self.stockfish.stdin.write(f"{command}\n")
-        self.stockfish.stdin.flush()
+        if self._stockfish.poll() is None and not self._has_quit_command_been_sent:
+            self._stockfish.stdin.write(f"{command}\n")
+            self._stockfish.stdin.flush()
+            if command == "quit":
+                self._has_quit_command_been_sent = True
 
     def _read_line(self) -> str:
-        if not self.stockfish.stdout:
+        if not self._stockfish.stdout:
             raise BrokenPipeError()
-        return self.stockfish.stdout.readline().strip()
+        return self._stockfish.stdout.readline().strip()
 
     def _set_option(self, name: str, value: Any) -> None:
         self._put(f"setoption name {name} value {value}")
@@ -543,5 +548,8 @@ def get_stockfish_major_version(self):
         return self._stockfish_major_version
 
     def __del__(self) -> None:
-        self._put("quit")
-        self.stockfish.kill()
+        if self._stockfish.poll() is None:
+            self._put("quit")
+            self._stockfish.kill()
+            while self._stockfish.poll() == None:
+                pass

tests/stockfish/test_models.py

@@ -166,6 +166,7 @@ def test_set_skill_level(self, stockfish):
         assert stockfish.get_parameters()["Skill Level"] == 20
 
     def test_set_elo_rating(self, stockfish):
+        stockfish.set_depth(2)
         stockfish.set_fen_position(
             "rnbqkbnr/ppp2ppp/3pp3/8/4P3/5N2/PPPP1PPP/RNBQKB1R w KQkq - 0 1"
         )
@@ -496,3 +497,30 @@ def test_benchmark_result_with_invalid_type(self, stockfish):
         result = stockfish.benchmark(params)
         # result should contain the last line of a successful method call
         assert result.split(" ")[0] == "Nodes/second"
+
+    def test_multiple_calls_to_del(self, stockfish):
+        assert stockfish._stockfish.poll() is None
+        assert not stockfish._has_quit_command_been_sent
+        stockfish.__del__()
+        assert stockfish._stockfish.poll() is not None
+        assert stockfish._has_quit_command_been_sent
+        stockfish.__del__()
+        assert stockfish._stockfish.poll() is not None
+        assert stockfish._has_quit_command_been_sent
+
+    def test_multiple_quit_commands(self, stockfish):
+        # Test multiple quit commands, and include a call to del too. All of
+        # them should run without causing some Exception.
+        assert stockfish._stockfish.poll() is None
+        assert not stockfish._has_quit_command_been_sent
+        stockfish._put("quit")
+        assert stockfish._has_quit_command_been_sent
+        stockfish._put("quit")
+        assert stockfish._has_quit_command_been_sent
+        stockfish.__del__()
+        assert stockfish._stockfish.poll() is not None
+        assert stockfish._has_quit_command_been_sent
+        stockfish._put(f"go depth {10}")
+        # Should do nothing, and change neither of the values below.
+        assert stockfish._stockfish.poll() is not None
+        assert stockfish._has_quit_command_been_sent