Refactor multiprocess test code to allow multiple child processes to be launched.

test/win/win_child_process.h

+// 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.
+
+#ifndef CRASHPAD_TEST_WIN_WIN_CHILD_PROCESS_H_
+#define CRASHPAD_TEST_WIN_WIN_CHILD_PROCESS_H_
+
+#include "base/basictypes.h"
+#include "base/memory/scoped_ptr.h"
+#include "util/file/file_io.h"
+#include "util/win/scoped_handle.h"
+
+namespace crashpad {
+namespace test {
+
+//! \brief Facilitates the launching of child processes from unit tests.
+class WinChildProcess {
+ public:
+  //! \brief Groups handles used to communicate with, observe, and manage a
+  //!     child process.
+  struct Handles {
+    //! \brief A handle to read from an anonymous pipe shared with the child
+    //!     process.
+    ScopedFileHANDLE read;
+    //! \brief A handle to write to an anonymous pipe shared with the child
+    //!     process.
+    ScopedFileHANDLE write;
+    //! \brief A handle to the child process.
+    ScopedKernelHANDLE process;
+  };
+
+  WinChildProcess();
+  virtual ~WinChildProcess() {}
+
+  //! \brief Returns true if the current process is a child process.
+  static bool IsChildProcess();
+
+  //! \brief Runs the child process defined by T if the current process is a
+  //!     child process; does not return in that case. Otherwise, returns.
+  template <class T>
+  static void EntryPoint() {
+    if (IsChildProcess()) {
+      T child_process;
+      // TODO(erikwright) force the client to subclass ChildProcess. Otherwise

[scottmg, 2015/06/25 04:13:24]

It's going to have to implement Run(), right? I don't understand what this
comment is trying to explain.

[erikwright (departed), 2015/06/25 14:36:02]

The TODO was out-of-date, sorry.

The point is that, given that this is a static method templated on T, the only
thing this method really requires is that T declare a method Run() whose return
value may be assigned to an int.

The static_cast adds an additional, important constraint.

+      // the pipe handshake might not occur, leading to a hang.
+      // TODO(erikwright): Use some form of static assert that gives a clear

[scottmg, 2015/06/25 04:13:24]

This second TODO isn't really actionable, so just remove it.

[erikwright (departed), 2015/06/25 14:36:02]

Done.

+      // error message.
+      static_cast<WinChildProcess*>(&child_process)->Run();
+      exit(0);

[scottmg, 2015/06/25 04:13:24]

The existing children (mostly?) do an exit(something) already. I wonder if
should instead make that part of the contract, remove the exit(0) and add a
ADD_FAILURE() here?

[erikwright (departed), 2015/06/25 14:36:02]

I would be more inclined to have Run() return an int (the exit code).

+    }
+  }
+
+  //! \brief Launches a child process and returns the Handles for that process.
+  //!     The process is guaranteed to be executing by the time this method
+  //!     returns. Returns null and logs a GTest failure in case of failure.
+  static scoped_ptr<Handles> Launch();
+
+ protected:
+  //! \brief Returns a handle to read from an anonymous pipe shared with the
+  //!     parent process.
+  //!
+  //! It is an error to call this after CloseReadPipe() has been called.
+  //!
+  //! \return The read pipe's file handle.
+  FileHandle ReadPipeHandle() const;
+
+  //! \brief Returns a handle to write to an anonymous pipe shared with the
+  //!     parent process.
+  //!
+  //! It is an error to call this after CloseWritePipe() has been called.
+  //!
+  //! \return The write pipe's file handle.
+  FileHandle WritePipeHandle() const;
+
+  //! \brief Closes the read pipe.
+  //!
+  //! ReadPipeHandle() must not be called after this.
+  void CloseReadPipe();
+
+  //! \brief Closes the write pipe.
+  //!
+  //! An attempt to read from the read pipe in the parent process will indicate
+  //! end-of-file. WritePipeHandle() must not be called after this.
+  void CloseWritePipe();
+
+ private:
+  //! \brief The subclass-provided child routine.
+  //!
+  //! Subclasses must implement this method to define how the child operates.
+  //! Subclasses may exit with a failure status by using `LOG(FATAL)`,
+  //! `abort()`, or similar. They may exit cleanly by returning from this
+  //! method. It is up to the client to observe and interpret the child's exit
+  //! code.
+  virtual void Run() = 0;
+
+  ScopedFileHANDLE pipe_read_;
+  ScopedFileHANDLE pipe_write_;
+
+  DISALLOW_COPY_AND_ASSIGN(WinChildProcess);
+};
+
+}  // namespace test
+}  // namespace crashpad
+
+#endif  // CRASHPAD_TEST_WIN_WIN_CHILD_PROCESS_H_