sim: Ensure draining is deterministic

The traversal of drainable objects could potentially be
non-deterministic when using an unordered set containing object
pointers. To ensure that the iteration is deterministic, we switch to
a vector. Note that the lookup and traversal of the drainable objects
is not performance critical, so the change has no negative consequences.

2 files changed, 11 insertions, 4 deletions

diff --git a/src/sim/drain.cc b/src/sim/drain.cc
index 085f781dc..bb8abd735 100644
--- a/src/sim/drain.cc
+++ b/src/sim/drain.cc
@@ -39,6 +39,8 @@
 
 #include "sim/drain.hh"
 
+#include <algorithm>
+
 #include "base/misc.hh"
 #include "base/trace.hh"
 #include "debug/Drain.hh"
@@ -126,6 +128,7 @@ DrainManager::preCheckpointRestore()
 void
 DrainManager::signalDrainDone()
 {
+    assert(_count > 0);
     if (--_count == 0) {
         DPRINTF(Drain, "All %u objects drained..\n", drainableCount());
         exitSimLoop("Finished drain", 0);
@@ -137,14 +140,18 @@ void
 DrainManager::registerDrainable(Drainable *obj)
 {
     std::lock_guard<std::mutex> lock(globalLock);
-    _allDrainable.insert(obj);
+    assert(std::find(_allDrainable.begin(), _allDrainable.end(), obj) ==
+           _allDrainable.end());
+    _allDrainable.push_back(obj);
 }
 
 void
 DrainManager::unregisterDrainable(Drainable *obj)
 {
     std::lock_guard<std::mutex> lock(globalLock);
-    _allDrainable.erase(obj);
+    auto o = std::find(_allDrainable.begin(), _allDrainable.end(), obj);
+    assert(o != _allDrainable.end());
+    _allDrainable.erase(o);
 }
 
 size_t
diff --git a/src/sim/drain.hh b/src/sim/drain.hh
index b3145e7ed..663946616 100644
--- a/src/sim/drain.hh
+++ b/src/sim/drain.hh
@@ -42,7 +42,7 @@
 
 #include <atomic>
 #include <mutex>
-#include <unordered_set>
+#include <vector>
 
 class Drainable;
 
@@ -162,7 +162,7 @@ class DrainManager
     mutable std::mutex globalLock;
 
     /** Set of all drainable objects */
-    std::unordered_set<Drainable *> _allDrainable;
+    std::vector<Drainable *> _allDrainable;
 
     /**
      * Number of objects still draining. This is flagged atomic since