Let the runqueue find the user selected scheduler dynamically

Searches the module (bb.runqueue) for any new style classes which are
instances of RunQueueScheduler, and uses the one whose 'name' attribute
matches the value of BB_SCHEDULER.

(Bitbake rev: 6497cedf9cfc03201250af816995dd2bd85c36ef)

Signed-off-by: Chris Larson <chris_larson@mentor.com>
Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>

bitbake/lib/bb/runqueue.py

@@ -70,10 +70,12 @@ runQueueCleanUp = 7
 runQueueComplete = 8
 runQueueChildProcess = 9
 
-class RunQueueScheduler:
+class RunQueueScheduler(object):
     """
     Control the order tasks are scheduled in.
     """
+    name = "basic"
+
     def __init__(self, runqueue):
         """
         The default scheduler just returns the first buildable task (the
@@ -101,6 +103,8 @@ class RunQueueSchedulerSpeed(RunQueueScheduler):
     A scheduler optimised for speed. The priority map is sorted by task weight,
     heavier weighted tasks (tasks needed by the most other tasks) are run first.
     """
+    name = "speed"
+
     def __init__(self, runqueue):
         """
         The priority map is sorted by task weight.
@@ -128,6 +132,8 @@ class RunQueueSchedulerCompletion(RunQueueSchedulerSpeed):
     well where disk space is at a premium and classes like OE's rm_work are in
     force.
     """
+    name = "completion"
+
     def __init__(self, runqueue):
         RunQueueSchedulerSpeed.__init__(self, runqueue)
         from copy import deepcopy
@@ -638,11 +644,15 @@ class RunQueue:
         # Check of higher length circular dependencies
         self.runq_weight = self.calculate_task_weights(endpoints)
 
-        # Decide what order to execute the tasks in, pick a scheduler
-        #self.sched = RunQueueScheduler(self)
-        if self.scheduler == "completion":
-            self.sched = RunQueueSchedulerCompletion(self)
+        schedulers = [obj for obj in globals().itervalues()
+                      if type(obj) is type and issubclass(obj, RunQueueScheduler)]
+        for scheduler in schedulers:
+            if self.scheduler == scheduler.name:
+                self.sched = scheduler(self)
+                break
         else:
+            bb.error("Invalid scheduler '%s', using default 'speed' scheduler" % self.scheduler)
+            bb.error("Available schedulers: %s" % ", ".join(obj.name for obj in schedulers))
             self.sched = RunQueueSchedulerSpeed(self)
 
         # Sanity Check - Check for multiple tasks building the same provider