Pathfinding dispatch improvements

* Simplify decision whether to update a path
* Prevent pathfinding threads from blocking each other

src/ripple_app/paths/PathRequest.cpp

@@ -29,7 +29,8 @@ const boost::shared_ptr<InfoSub>& subscriber, int id, PathRequests& owner,
     , wpSubscriber (subscriber)
     , jvStatus (Json::objectValue)
     , bValid (false)
-    , iLastIndex (0)
+    , mLastIndex (0)
+    , mInProgress (false)
     , iLastLevel (0)
     , bLastSuccess (false)
     , iIdentifier (id)
@@ -77,38 +78,43 @@ bool PathRequest::isValid ()
 
 bool PathRequest::isNew ()
 {
-     // does this path request still need its first full path
-     return iLastIndex.load() == 0;
+    ScopedLockType sl (mIndexLock);
+
+    // does this path request still need its first full path
+    return mLastIndex == 0;
 }
 
 bool PathRequest::needsUpdate (bool newOnly, LedgerIndex index)
 {
-    LedgerIndex lastIndex = iLastIndex.load();
-    for (;;)
+    ScopedLockType sl (mIndexLock);
+
+    if (mInProgress)
     {
-        if (newOnly)
-        {
-            // Is this request new
-            if (lastIndex != 0)
-                return false;
-
-            // This thread marks this request handled
-            if (iLastIndex.compare_exchange_weak (lastIndex, 1,
-                    std::memory_order_release, std::memory_order_relaxed))
-                return true;
-        }
-        else
-        {
-            // Has the request already been handled?
-            if (lastIndex >= index)
-                return false;
-
-            // This thread marks this request handled
-            if (iLastIndex.compare_exchange_weak (lastIndex, index,
-                    std::memory_order_release, std::memory_order_relaxed))
-                return true;
-        }
+        // Another thread is handling this
+        return false;
     }
+
+    if (newOnly && (mLastIndex != 0))
+    {
+        // Only handling new requests, this isn't new
+        return false;
+    }
+
+    if (mLastIndex >= index)
+    {
+        return false;
+    }
+
+    mInProgress = true;
+    return true;
+}
+
+void PathRequest::updateComplete ()
+{
+    ScopedLockType sl (mIndexLock);
+
+    assert (mInProgress);
+    mInProgress = false;
 }
 
 bool PathRequest::isValid (RippleLineCache::ref crCache)

src/ripple_app/paths/PathRequest.h

@@ -57,6 +57,7 @@ public:
     bool        isValid ();
     bool        isNew ();
     bool        needsUpdate (bool newOnly, LedgerIndex index);
+    void        updateComplete ();
     Json::Value getStatus ();
 
     Json::Value doCreate (const boost::shared_ptr<Ledger>&, const RippleLineCache::pointer&,
@@ -93,7 +94,9 @@ private:
 
     bool                            bValid;
 
-    std::atomic<LedgerIndex>        iLastIndex;
+    LockType                        mIndexLock;
+    LedgerIndex                     mLastIndex;
+    bool                            mInProgress;
 
     int                             iLastLevel;
     bool                            bLastSuccess;

src/ripple_app/paths/PathRequests.cpp

@@ -90,6 +90,7 @@ void PathRequests::updateAll (Ledger::ref inLedger, CancelCallback shouldCancel)
                         if (!ipSub->getConsumer ().warn ())
                         {
                             Json::Value update = pRequest->doUpdate (cache, false);
+                            pRequest->updateComplete ();
                             update["type"] = "path_find";
                             ipSub->send (update, false);
                             remove = false;