win: Implement and use ScopedProcessSuspend

util/win/scoped_process_suspend_test.cc

+// Copyright 2015 The Crashpad Authors. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "util/win/scoped_process_suspend.h"
+
+#include <tlhelp32.h>
+
+#include <algorithm>
+#include <vector>
+
+#include "gtest/gtest.h"
+#include "test/win/win_child_process.h"
+
+namespace crashpad {
+namespace test {
+namespace {
+
+// There is no such thing as process suspension on Windows, only thread
+// suspension, so we verify that all threads match the desired suspend count.

[Mark Mentovai, 2015/09/04 15:57:50]

This comment is a little terse given that the implementation calls an ntdll
function named NtSuspendProcess(). Do you mean that there’s no per-process
suspend count, and that NtSuspendProcess increments each thread’s suspend count?

(If so, for curiosity: does NtSuspendProcess() prevent new threads from being
created while it’s running too?)

[scottmg, 2015/09/04 22:05:38]

That's right.
Yes, there's a process lock taken in the kernel during suspend, resume, and
create. That's the main reason for NtSuspendProcess over just iterating threads
and calling SuspendThread on them, though it also seems a bit tidier.

+bool SuspendCountMatches(HANDLE process, DWORD desired_suspend_count) {
+  DWORD process_id = GetProcessId(process);
+
+  ScopedKernelHANDLE snapshot(CreateToolhelp32Snapshot(TH32CS_SNAPTHREAD, 0));
+  if (snapshot.is_valid()) {
+    THREADENTRY32 te;
+    te.dwSize = sizeof(te);
+    if (Thread32First(snapshot.get(), &te)) {
+      do {
+        if (te.dwSize >= offsetof(THREADENTRY32, th32OwnerProcessID) +
+                             sizeof(te.th32OwnerProcessID)) {
+          if (te.th32OwnerProcessID == process_id) {

[Mark Mentovai, 2015/09/04 15:57:50]

if (a) { if (b) { … }} → if (a && b) { … }

[scottmg, 2015/09/04 22:05:38]

Done.

+            ScopedKernelHANDLE thread(
+                OpenThread(THREAD_ALL_ACCESS, false, te.th32ThreadID));
+            DWORD result = SuspendThread(thread.get());
+            EXPECT_NE(result, 0xffffffff);
+            if (result >= 0)
+              ResumeThread(thread.get());
+            if (result != desired_suspend_count)
+              return false;
+          }
+        }
+        te.dwSize = sizeof(te);
+      } while (Thread32Next(snapshot.get(), &te));
+    }

[Mark Mentovai, 2015/09/04 15:57:50]

else return false? Better yet: if (a) { … } else { return false; } → if (!a) {
return false; } …

[scottmg, 2015/09/04 22:05:38]

Done.

+  }

[Mark Mentovai, 2015/09/04 15:57:50]

Same.

[scottmg, 2015/09/04 22:05:38]

Done.

+
+  return true;
+}
+
+class ScopedProcessSuspendTest final : public WinChildProcess {
+ public:
+  ScopedProcessSuspendTest() : WinChildProcess() {}
+  ~ScopedProcessSuspendTest() {}
+
+ private:
+  int Run() override {
+    char c;
+    // Wait for notification from parent.
+    EXPECT_TRUE(LoggingReadFile(ReadPipeHandle(), &c, sizeof(c)));
+    EXPECT_EQ(c, ' ');

[Mark Mentovai, 2015/09/04 15:57:50]

For gtest _EQ macros, it’s (expected, actual).

[scottmg, 2015/09/04 22:05:38]

Still, eh? Done.

+    return EXIT_SUCCESS;
+  }
+
+  DISALLOW_COPY_AND_ASSIGN(ScopedProcessSuspendTest);
+};
+
+TEST(ScopedProcessSuspend, ScopedProcessSuspend) {
+  WinChildProcess::EntryPoint<ScopedProcessSuspendTest>();
+  scoped_ptr<WinChildProcess::Handles> handles = WinChildProcess::Launch();
+
+  EXPECT_TRUE(SuspendCountMatches(handles->process.get(), 0));
+
+  {
+    ScopedProcessSuspend suspend(handles->process.get());
+    EXPECT_TRUE(SuspendCountMatches(handles->process.get(), 1));
+
+    {
+      ScopedProcessSuspend suspend(handles->process.get());
+      EXPECT_TRUE(SuspendCountMatches(handles->process.get(), 2));
+    }
+
+    EXPECT_TRUE(SuspendCountMatches(handles->process.get(), 1));
+  }
+
+  EXPECT_TRUE(SuspendCountMatches(handles->process.get(), 0));
+
+  // Tell the child it's OK to terminate.
+  char c = ' ';
+  EXPECT_TRUE(WriteFile(handles->write.get(), &c, sizeof(c)));
+}
+
+}  // namespace
+}  // namespace test
+}  // namespace crashpad