fix send_signal race

Lib/asyncio/base_subprocess.py

@@ -1,6 +1,8 @@
 import collections
 import subprocess
 import warnings
+import os
+import signal
 
 from . import protocols
 from . import transports
@@ -144,15 +146,16 @@ def _check_proc(self):
 
     def send_signal(self, signal):
         self._check_proc()
-        self._proc.send_signal(signal)
+        try:
+            os.kill(self._proc.pid, signal)
+        except ProcessLookupError:
+            pass
 
     def terminate(self):
-        self._check_proc()
-        self._proc.terminate()
+        self.send_signal(signal.SIGTERM)
 
     def kill(self):
-        self._check_proc()
-        self._proc.kill()
+        self.send_signal(signal.SIGKILL)
 
     async def _connect_pipes(self, waiter):
         try:

Lib/test/test_asyncio/test_subprocess.py

@@ -864,6 +864,20 @@ async def main():
 
         self.loop.run_until_complete(main())
 
+    def test_subprocess_send_signal_race(self):
+        # See https://github.com/python/cpython/issues/87744
+        async def main():
+            for _ in range(10):
+                proc = await asyncio.create_subprocess_exec('sleep', '0.1')
+                await asyncio.sleep(0.1)
+                try:
+                    proc.send_signal(signal.SIGUSR1)
+                except ProcessLookupError:
+                    pass
+                self.assertNotEqual(await proc.wait(), 255)
+
+        self.loop.run_until_complete(main())
+
 
 if sys.platform != 'win32':
     # Unix