Nice automatic updates up to a point, then renice if necessary.

utils.h

 // Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROMEOS_PLATFORM_UPDATE_ENGINE_UTILS_H__
 #define CHROMEOS_PLATFORM_UPDATE_ENGINE_UTILS_H__
 
 #include <errno.h>
+
 #include <algorithm>
 #include <set>
 #include <string>
 #include <vector>
+
 #include <glib.h>
+
 #include "update_engine/action.h"
 #include "update_engine/action_processor.h"
 
 namespace chromeos_update_engine {
 
 namespace utils {
 
 // Returns true if this is an official Chrome OS build, false
 // otherwise. Currently, this routine errs on the official build side
 // -- if it doesn't recognize the update track as non-official, it
@@ skipping 152 matching lines @@
 // or something with equivalent funcionality to interpret those.
 const std::string BootDevice();
 
 // Returns the currently booted kernel device, "dev/sda2", for example.
 // Client must pass in the boot device. The suggested calling convention
 // is: BootKernelDevice(BootDevice()).
 // This function works by doing string modification on boot_device.
 // Returns empty string on failure.
 const std::string BootKernelDevice(const std::string& boot_device);
 
+enum ProcessPriority {
+  kProcessPriorityHigh = -10,
+  kProcessPriorityNormal = 0,
+  kProcessPriorityLow = 10,
+};
+
+// Compares process priorities and returns an integer that is less
+// than, equal to or greater than 0 if |priority_lhs| is,
+// respectively, lower than, same as or higher than |priority_rhs|.
+int ComparePriorities(ProcessPriority priority_lhs,
+                      ProcessPriority priority_rhs);
+
+// Sets the current process priority to |priority|. Returns true on
+// success, false otherwise.
+bool SetProcessPriority(ProcessPriority priority);
 
 }  // namespace utils
 
 // Class to unmount FS when object goes out of scope
 class ScopedFilesystemUnmounter {
  public:
   explicit ScopedFilesystemUnmounter(const std::string& mountpoint)
       : mountpoint_(mountpoint) {}
   ~ScopedFilesystemUnmounter() {
     utils::UnmountFilesystem(mountpoint_);
@@ skipping 115 matching lines @@
     bool _success = (_x);                                                      \
     if (!_success) {                                                           \
       LOG(ERROR) << #_x " failed.";                                            \
       return;                                                                  \
     }                                                                          \
   } while (0)
 
 
 
 #endif  // CHROMEOS_PLATFORM_UPDATE_ENGINE_UTILS_H__