sim: make Python Root object a singleton

Enforce that the Python Root SimObject is instantiated only
once.  The C++ Root object already panics if more than one is
created.  This change avoids the need to track what the root
object is, since it's available from Root.getInstance() (if it
exists).  It's now redundant to have the user pass the root
object to functions like instantiate(), checkpoint(), and
restoreCheckpoint(), so that arg is gone.  Users who use
configs/common/Simulate.py should not notice.

10 files changed, 53 insertions, 20 deletions

diff --git a/configs/common/Simulation.py b/configs/common/Simulation.py
index 905e435d3..0393b0dfa 100644
--- a/configs/common/Simulation.py
+++ b/configs/common/Simulation.py
@@ -190,7 +190,7 @@ def run(options, root, testsys, cpu_class):
             for i in xrange(np):
                 testsys.cpu[i].max_insts_any_thread = offset
 
-    m5.instantiate(root)
+    m5.instantiate()
 
     if options.checkpoint_restore != None:
         from os.path import isdir, exists
@@ -207,7 +207,7 @@ def run(options, root, testsys, cpu_class):
                 fatal("Unable to find checkpoint directory %s", checkpoint_dir)
 
             print "Restoring checkpoint ..."
-            m5.restoreCheckpoint(root, checkpoint_dir)
+            m5.restoreCheckpoint(checkpoint_dir)
             print "Done."
         elif options.simpoint:
             # assume workload 0 has the simpoint
@@ -224,7 +224,7 @@ def run(options, root, testsys, cpu_class):
                       options.bench, options.checkpoint_restore)
 
             print "Restoring checkpoint ..."
-            m5.restoreCheckpoint(root,checkpoint_dir)
+            m5.restoreCheckpoint(checkpoint_dir)
             print "Done."
         else:
             dirs = listdir(cptdir)
@@ -246,8 +246,8 @@ def run(options, root, testsys, cpu_class):
             maxtick = maxtick - int(cpts[cpt_num - 1])
 
             ## Restore the checkpoint
-            m5.restoreCheckpoint(root,
-                    joinpath(cptdir, "cpt.%s" % cpts[cpt_num - 1]))
+            m5.restoreCheckpoint(joinpath(cptdir,
+                                          "cpt.%s" % cpts[cpt_num - 1]))
 
     if options.standard_switch or cpu_class:
         if options.standard_switch:
@@ -324,7 +324,7 @@ def run(options, root, testsys, cpu_class):
 
             if exit_event.getCause() == \
                    "a thread reached the max instruction count":
-                m5.checkpoint(root, joinpath(cptdir, "cpt.%s.%d" % \
+                m5.checkpoint(joinpath(cptdir, "cpt.%s.%d" % \
                         (options.bench, checkpoint_inst)))
                 print "Checkpoint written."
                 num_checkpoints += 1
@@ -341,7 +341,7 @@ def run(options, root, testsys, cpu_class):
                 exit_event = m5.simulate(when - m5.curTick())
 
             if exit_event.getCause() == "simulate() limit reached":
-                m5.checkpoint(root, joinpath(cptdir, "cpt.%d"))
+                m5.checkpoint(joinpath(cptdir, "cpt.%d"))
                 num_checkpoints += 1
 
             sim_ticks = when
@@ -358,7 +358,7 @@ def run(options, root, testsys, cpu_class):
                     while exit_event.getCause() == "checkpoint":
                         exit_event = m5.simulate(sim_ticks - m5.curTick())
                     if exit_event.getCause() == "simulate() limit reached":
-                        m5.checkpoint(root, joinpath(cptdir, "cpt.%d"))
+                        m5.checkpoint(joinpath(cptdir, "cpt.%d"))
                         num_checkpoints += 1
 
             if exit_event.getCause() != "simulate() limit reached":
@@ -371,7 +371,7 @@ def run(options, root, testsys, cpu_class):
         exit_event = m5.simulate(maxtick)
 
         while exit_event.getCause() == "checkpoint":
-            m5.checkpoint(root, joinpath(cptdir, "cpt.%d"))
+            m5.checkpoint(joinpath(cptdir, "cpt.%d"))
             num_checkpoints += 1
             if num_checkpoints == max_checkpoints:
                 exit_cause = "maximum %d checkpoints dropped" % max_checkpoints
@@ -385,5 +385,5 @@ def run(options, root, testsys, cpu_class):
     print 'Exiting @ cycle %i because %s' % (m5.curTick(), exit_cause)
 
     if options.checkpoint_at_end:
-        m5.checkpoint(root, joinpath(cptdir, "cpt.%d"))
+        m5.checkpoint(joinpath(cptdir, "cpt.%d"))
 
diff --git a/configs/example/memtest-ruby.py b/configs/example/memtest-ruby.py
index 709d31844..16d86f0bc 100644
--- a/configs/example/memtest-ruby.py
+++ b/configs/example/memtest-ruby.py
@@ -129,7 +129,7 @@ else:
 m5.ticks.setGlobalFrequency('1ns')
 
 # instantiate configuration
-m5.instantiate(root)
+m5.instantiate()
 
 # simulate until program terminates
 exit_event = m5.simulate(options.maxtick)
diff --git a/configs/example/memtest.py b/configs/example/memtest.py
index d4497092b..0713dd241 100644
--- a/configs/example/memtest.py
+++ b/configs/example/memtest.py
@@ -181,7 +181,7 @@ else:
 m5.ticks.setGlobalFrequency('1ns')
 
 # instantiate configuration
-m5.instantiate(root)
+m5.instantiate()
 
 # simulate until program terminates
 exit_event = m5.simulate(options.maxtick)
diff --git a/configs/example/rubytest.py b/configs/example/rubytest.py
index 13b862756..c9cf0aba4 100644
--- a/configs/example/rubytest.py
+++ b/configs/example/rubytest.py
@@ -118,7 +118,7 @@ root.system.mem_mode = 'timing'
 m5.ticks.setGlobalFrequency('1ns')
 
 # instantiate configuration
-m5.instantiate(root)
+m5.instantiate()
 
 # simulate until program terminates
 exit_event = m5.simulate(options.maxtick)
diff --git a/configs/splash2/cluster.py b/configs/splash2/cluster.py
index 45c9ede82..77591dc62 100644
--- a/configs/splash2/cluster.py
+++ b/configs/splash2/cluster.py
@@ -292,7 +292,7 @@ if options.timing or options.detailed:
     root.system.mem_mode = 'timing'
 
 # instantiate configuration
-m5.instantiate(root)
+m5.instantiate()
 
 # simulate until program terminates
 if options.maxtick:
diff --git a/configs/splash2/run.py b/configs/splash2/run.py
index 95ec790ba..24faade17 100644
--- a/configs/splash2/run.py
+++ b/configs/splash2/run.py
@@ -276,7 +276,7 @@ if options.timing or options.detailed:
     root.system.mem_mode = 'timing'
 
 # instantiate configuration
-m5.instantiate(root)
+m5.instantiate()
 
 # simulate until program terminates
 if options.maxtick:
diff --git a/src/python/m5/SimObject.py b/src/python/m5/SimObject.py
index 3b84d6000..8e14b63d2 100644
--- a/src/python/m5/SimObject.py
+++ b/src/python/m5/SimObject.py
@@ -623,7 +623,7 @@ class SimObject(object):
 
     def path(self):
         if not self._parent:
-            return 'root'
+            return '(orphan)'
         ppath = self._parent.path()
         if ppath == 'root':
             return self._name
diff --git a/src/python/m5/simulate.py b/src/python/m5/simulate.py
index e43f90173..2db5c6952 100644
--- a/src/python/m5/simulate.py
+++ b/src/python/m5/simulate.py
@@ -39,13 +39,19 @@ from main import options
 import SimObject
 import ticks
 import objects
+from util import fatal
 
 # define a MaxTick parameter
 MaxTick = 2**63 - 1
 
 # The final hook to generate .ini files.  Called from the user script
 # once the config is built.
-def instantiate(root):
+def instantiate():
+    root = objects.Root.getInstance()
+
+    if not root:
+        fatal("Need to instantiate Root() before calling instantiate()")
+
     # we need to fix the global frequency
     ticks.fixGlobalFrequency()
 
@@ -136,7 +142,8 @@ def drain(root):
 def resume(root):
     root.resume()
 
-def checkpoint(root, dir):
+def checkpoint(dir):
+    root = objects.Root.getInstance()
     if not isinstance(root, objects.Root):
         raise TypeError, "Checkpoint must be called on a root object."
     doDrain(root)
@@ -144,7 +151,8 @@ def checkpoint(root, dir):
     internal.core.serializeAll(dir)
     resume(root)
 
-def restoreCheckpoint(root, dir):
+def restoreCheckpoint(dir):
+    root = objects.Root.getInstance()
     print "Restoring from checkpoint"
     internal.core.unserializeAll(dir)
     need_resume.append(root)
diff --git a/src/sim/Root.py b/src/sim/Root.py
index fff998e0d..c7404a11f 100644
--- a/src/sim/Root.py
+++ b/src/sim/Root.py
@@ -28,7 +28,32 @@
 
 from m5.SimObject import SimObject
 from m5.params import *
+from m5.util import fatal
 
 class Root(SimObject):
+
+    _the_instance = None
+
+    def __new__(cls, **kwargs):
+        if Root._the_instance:
+            fatal("Attempt to allocate multiple instances of Root.")
+            return None
+
+        # first call: allocate the unique instance
+        #
+        # If SimObject ever implements __new__, we may want to pass
+        # kwargs here, but for now this goes straight to
+        # object.__new__ which prints an ugly warning if you pass it
+        # args.  Seems like a bad design but that's the way it is.
+        Root._the_instance = SimObject.__new__(cls)
+        return Root._the_instance
+        
+    @classmethod
+    def getInstance(cls):
+        return Root._the_instance
+
+    def path(self):
+        return 'root'
+
     type = 'Root'
     dummy = Param.Int(0, "We don't support objects without params")
diff --git a/tests/run.py b/tests/run.py
index 1e58f0283..f4105fb41 100644
--- a/tests/run.py
+++ b/tests/run.py
@@ -78,7 +78,7 @@ sys.path.append(joinpath(tests_root, category, name))
 execfile(joinpath(tests_root, category, name, 'test.py'))
 
 # instantiate configuration
-m5.instantiate(root)
+m5.instantiate()
 
 # simulate until program terminates
 exit_event = m5.simulate(maxtick)