[flutter_tool] Kill a timing out process before trying to drain its stdout/err streams (#40159)

packages/flutter_tools/lib/src/base/process.dart

@@ -275,13 +275,23 @@ Future<RunResult> runAsync(
 
     int exitCode;
     exitCode = await process.exitCode.timeout(timeout, onTimeout: () {
+      // The process timed out. Kill it.
+      processManager.killPid(process.pid);
       return null;
     });
 
     String stdoutString;
     String stderrString;
     try {
-      await Future.wait<void>(<Future<void>>[stdoutFuture, stderrFuture]);
+      Future<void> stdioFuture =
+          Future.wait<void>(<Future<void>>[stdoutFuture, stderrFuture]);
+      if (exitCode == null) {
+        // If we had to kill the process for a timeout, only wait a short time
+        // for the stdio streams to drain in case killing the process didn't
+        // work.
+        stdioFuture = stdioFuture.timeout(const Duration(seconds: 1));
+      }
+      await stdioFuture;
     } catch (_) {
       // Ignore errors on the process' stdout and stderr streams. Just capture
       // whatever we got, and use the exit code
@@ -299,9 +309,6 @@ Future<RunResult> runAsync(
       return runResult;
     }
 
-    // The process timed out. Kill it.
-    processManager.killPid(process.pid);
-
     // If we are out of timeoutRetries, throw a ProcessException.
     if (timeoutRetries < 0) {
       throw ProcessException(cmd[0], cmd.sublist(1),

packages/flutter_tools/test/general.shard/base/process_test.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:async';
+
 import 'package:flutter_tools/src/base/io.dart';
 import 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/base/platform.dart';
@@ -103,13 +105,13 @@ void main() {
       // MockProcessManager has an implementation of start() that returns the
       // result of processFactory.
       flakyProcessManager = MockProcessManager();
+    });
+
+    testUsingContext('flaky process fails without retry', () async {
       flakyProcessManager.processFactory = flakyProcessFactory(
         flakes: 1,
         delay: delay,
       );
-    });
-
-    testUsingContext('flaky process fails without retry', () async {
       final RunResult result = await runAsync(
         <String>['dummy'],
         timeout: delay + const Duration(seconds: 1),
@@ -120,6 +122,10 @@ void main() {
     });
 
     testUsingContext('flaky process succeeds with retry', () async {
+      flakyProcessManager.processFactory = flakyProcessFactory(
+        flakes: 1,
+        delay: delay,
+      );
       final RunResult result = await runAsync(
         <String>['dummy'],
         timeout: delay - const Duration(milliseconds: 500),
@@ -131,6 +137,22 @@ void main() {
     });
 
     testUsingContext('flaky process generates ProcessException on timeout', () async {
+      final Completer<List<int>> flakyStderr = Completer<List<int>>();
+      final Completer<List<int>> flakyStdout = Completer<List<int>>();
+      flakyProcessManager.processFactory = flakyProcessFactory(
+        flakes: 1,
+        delay: delay,
+        stderr: () => Stream<List<int>>.fromFuture(flakyStderr.future),
+        stdout: () => Stream<List<int>>.fromFuture(flakyStdout.future),
+      );
+      when(flakyProcessManager.killPid(any)).thenAnswer((_) {
+        // Don't let the stderr stream stop until the process is killed. This
+        // ensures that runAsync() does not delay killing the process until
+        // stdout and stderr are drained (which won't happen).
+        flakyStderr.complete(<int>[]);
+        flakyStdout.complete(<int>[]);
+        return true;
+      });
       expect(() async => await runAsync(
         <String>['dummy'],
         timeout: delay - const Duration(milliseconds: 500),