Fix dart:io Process class on the Windows plaform, which had some race conditions.

runtime/bin/process_win.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include <process.h>
 
 #include "bin/builtin.h"
 #include "bin/process.h"
 #include "bin/eventhandler.h"
 #include "bin/thread.h"
@@ skipping 50 matching lines @@
   // Link to next ProcessInfo object in the singly-linked list.
   ProcessInfo* next_;
 };
 
 
 // Singly-linked list of ProcessInfo objects for all active processes
 // started from Dart.
 class ProcessInfoList {
  public:
   static void AddProcess(DWORD pid, HANDLE handle, HANDLE pipe) {
-    // Create a wait operation for the process handle to extract
-    // the exit code.
+    // Register a callback to extract the exit code, when the process
+    // is signaled.  The callback runs in a independent thread from the OS pool.
+    // Because the callback depends on the process list containing
+    // the process, lock the mutex until the process is added to the list.
+    MutexLocker locker(&mutex_);
     HANDLE wait_handle = INVALID_HANDLE_VALUE;
     BOOL success = RegisterWaitForSingleObject(
         &wait_handle,
         handle,
         &ExitCodeCallback,
         reinterpret_cast<void*>(pid),
         INFINITE,
         WT_EXECUTEONLYONCE);
     if (!success) {
       FATAL("Failed to register exit code wait operation.");
     }
     ProcessInfo* info = new ProcessInfo(pid, handle, wait_handle, pipe);
-    // Now mutate the process list under the mutex.
-    MutexLocker locker(&mutex_);
+    // Mutate the process list under the mutex.
     info->set_next(active_processes_);
     active_processes_ = info;
   }
 
   static bool LookupProcess(DWORD pid,
                             HANDLE* handle,
                             HANDLE* wait_handle,
                             HANDLE* pipe) {
     MutexLocker locker(&mutex_);
     ProcessInfo* current = active_processes_;
@@ skipping 405 matching lines @@
 
 bool Process::Kill(intptr_t id, int signal) {
   USE(signal);  // signal is not used on windows.
   HANDLE process_handle;
   HANDLE wait_handle;
   HANDLE exit_pipe;
   bool success = ProcessInfoList::LookupProcess(id,
                                                 &process_handle,
                                                 &wait_handle,
                                                 &exit_pipe);
-  ASSERT(success);
+  if (!success) {
+    return true;  // The process has already died.  Report a successful kill.

[Anders Johnsen, 2012/08/21 14:33:47]

Returning true here is inconsistent with linux/mac. Either update the
process.kill comment or change?

+  }
   BOOL result = TerminateProcess(process_handle, -1);
   if (!result) {
     return false;
   }
   return true;
 }
 
 
 void Process::TerminateExitCodeHandler() {
   // Nothing needs to be done on Windows.
 }
 
 
 intptr_t Process::CurrentProcessId() {
   return static_cast<intptr_t>(GetCurrentProcessId());
 }