sim: Refactor and simplify the drain API

The drain() call currently passes around a DrainManager pointer, which
is now completely pointless since there is only ever one global
DrainManager in the system. It also contains vestiges from the time
when SimObjects had to keep track of their child objects that needed
draining.

This changeset moves all of the DrainState handling to the Drainable
base class and changes the drain() and drainResume() calls to reflect
this. Particularly, the drain() call has been updated to take no
parameters (the DrainManager argument isn't needed) and return a
DrainState instead of an unsigned integer (there is no point returning
anything other than 0 or 1 any more). Drainable objects should return
either DrainState::Draining (equivalent to returning 1 in the old
system) if they need more time to drain or DrainState::Drained
(equivalent to returning 0 in the old system) if they are already in a
consistent state. Returning DrainState::Running is considered an
error.

Drain done signalling is now done through the signalDrainDone() method
in the Drainable class instead of using the DrainManager directly. The
new call checks if the state of the object is DrainState::Draining
before notifying the drain manager. This means that it is safe to call
signalDrainDone() without first checking if the simulator has
requested draining. The intention here is to reduce the code needed to
implement draining in simple objects.

2 files changed, 9 insertions, 16 deletions

diff --git a/src/cpu/testers/traffic_gen/traffic_gen.cc b/src/cpu/testers/traffic_gen/traffic_gen.cc
index 0fc8848fb..984c9950d 100644
--- a/src/cpu/testers/traffic_gen/traffic_gen.cc
+++ b/src/cpu/testers/traffic_gen/traffic_gen.cc
@@ -63,8 +63,7 @@ TrafficGen::TrafficGen(const TrafficGenParams* p)
       port(name() + ".port", *this),
       retryPkt(NULL),
       retryPktTick(0),
-      updateEvent(this),
-      drainManager(NULL)
+      updateEvent(this)
 {
 }
 
@@ -118,12 +117,12 @@ TrafficGen::initState()
     }
 }
 
-unsigned int
-TrafficGen::drain(DrainManager *dm)
+DrainState
+TrafficGen::drain()
 {
     if (!updateEvent.scheduled()) {
         // no event has been scheduled yet (e.g. switched from atomic mode)
-        return 0;
+        return DrainState::Drained;
     }
 
     if (retryPkt == NULL) {
@@ -131,10 +130,9 @@ TrafficGen::drain(DrainManager *dm)
         nextPacketTick = MaxTick;
         nextTransitionTick = MaxTick;
         deschedule(updateEvent);
-        return 0;
+        return DrainState::Drained;
     } else {
-        drainManager = dm;
-        return 1;
+        return DrainState::Draining;
     }
 }
 
@@ -488,7 +486,7 @@ TrafficGen::recvReqRetry()
         retryPktTick = 0;
         retryTicks += delay;
 
-        if (drainManager == NULL) {
+        if (drainState() != DrainState::Draining) {
             // packet is sent, so find out when the next one is due
             nextPacketTick = states[currState]->nextPacketTick(elasticReq,
                                                                delay);
@@ -498,9 +496,7 @@ TrafficGen::recvReqRetry()
             // shut things down
             nextPacketTick = MaxTick;
             nextTransitionTick = MaxTick;
-            drainManager->signalDrainDone();
-            // Clear the drain event once we're done with it.
-            drainManager = NULL;
+            signalDrainDone();
         }
     }
 }
diff --git a/src/cpu/testers/traffic_gen/traffic_gen.hh b/src/cpu/testers/traffic_gen/traffic_gen.hh
index ba7fda7dd..8b71443f9 100644
--- a/src/cpu/testers/traffic_gen/traffic_gen.hh
+++ b/src/cpu/testers/traffic_gen/traffic_gen.hh
@@ -176,9 +176,6 @@ class TrafficGen : public MemObject
     /** Event for scheduling updates */
     EventWrapper<TrafficGen, &TrafficGen::update> updateEvent;
 
-    /** Manager to signal when drained */
-    DrainManager* drainManager;
-
     /** Count the number of generated packets. */
     Stats::Scalar numPackets;
 
@@ -201,7 +198,7 @@ class TrafficGen : public MemObject
 
     void initState();
 
-    unsigned int drain(DrainManager *dm);
+    DrainState drain() M5_ATTR_OVERRIDE;
 
     void serialize(CheckpointOut &cp) const M5_ATTR_OVERRIDE;
     void unserialize(CheckpointIn &cp) M5_ATTR_OVERRIDE;