PY-34436 Fix Python 3.7 multiprocess debugging

python/helpers/pydev/pydevd.py

@@ -173,10 +173,22 @@ class CheckOutputThread(PyDBDaemonThread):
                 except:
                     traceback.print_exc()
 
+                self.wait_pydb_threads_to_finish()
+
                 self.killReceived = True
 
             self.py_db.check_output_redirect()
 
+    def wait_pydb_threads_to_finish(self, timeout=0.5):
+        pydev_log.debug("Waiting for pydb daemon threads to finish")
+        pydb_daemon_threads = self.created_pydb_daemon_threads
+        started_at = time.time()
+        while time.time() < started_at + timeout:
+            if len(pydb_daemon_threads) == 1 and pydb_daemon_threads.get(self, None):
+                return
+            time.sleep(0.01)
+        pydev_log.debug("The following pydb threads may not finished correctly: %s"
+                        % ', '.join([t.getName() for t in pydb_daemon_threads if t is not self]))
 
     def do_kill_pydev_thread(self):
         self.killReceived = True
@@ -1311,6 +1323,9 @@ def _locked_settrace(
     global bufferStdOutToServer
     global bufferStdErrToServer
 
+    # Reset created PyDB daemon threads after fork - parent threads don't exist in a child process.
+    PyDBDaemonThread.created_pydb_daemon_threads = {}
+
     if not connected:
         pydevd_vm_type.setup_type()
 

python/testData/debug/test_multiprocess_pool.py

@@ -0,0 +1,9 @@
+from __future__ import print_function
+from multiprocessing import Pool
+from time import sleep
+pool = Pool(4)
+pool.map(print, ['1', '2', '3'])
+pool.close()
+pool.join()
+sleep(1)
+print('Done')

python/testSrc/com/jetbrains/env/python/PythonDebuggerTest.java

@@ -827,6 +827,22 @@ public class PythonDebuggerTest extends PyEnvTestCase {
     });
   }
 
+  @Test
+  public void testMultiprocessPool() {
+    runPythonTest(new PyDebuggerTask("/debug", "test_multiprocess_pool.py") {
+      @Override
+      protected void init() {
+        setMultiprocessDebug(true);
+      }
+
+      @Override
+      public void testing() throws Exception {
+        waitForOutput("Done");
+        assertFalse(output().contains("KeyboardInterrupt"));
+      }
+    });
+  }
+
   @Test
   public void testPythonSubprocessWithCParameter() {
     runPythonTest(new PyDebuggerTask("/debug", "test_python_subprocess_with_c_parameter.py") {