Avoid mining on empty blocks.

Protocol bump.

alethzero/Main.ui

@@ -184,7 +184,7 @@
     <addaction name="paranoia"/>
     <addaction name="killBlockchain"/>
     <addaction name="inject"/>
-    <addaction name="clearPending"/>
+    <addaction name="forceMining"/>
    </widget>
    <addaction name="menu_File"/>
    <addaction name="menu_Network"/>
@@ -1559,9 +1559,12 @@ font-size: 14pt</string>
     <string>Ctrl+F10</string>
    </property>
   </action>
-  <action name="clearPending">
+  <action name="forceMining">
+   <property name="checkable">
+    <bool>true</bool>
+   </property>
    <property name="text">
-    <string>&amp;Clear Pending</string>
+    <string>&amp;Force Mining</string>
    </property>
   </action>
   <action name="dumpTraceStorage">

alethzero/MainWin.cpp

@@ -327,9 +327,9 @@ void Main::onNewPending()
 	refreshAccounts();
 }
 
-void Main::on_clearPending_triggered()
+void Main::on_forceMining_triggered()
 {
-	m_client->clearPending();
+	m_client->setForceMining(ui->forceMining->isChecked());
 }
 
 void Main::load(QString _s)
@@ -485,6 +485,7 @@ void Main::writeSettings()
 	s.setValue("upnp", ui->upnp->isChecked());
 	s.setValue("forceAddress", ui->forceAddress->text());
 	s.setValue("usePast", ui->usePast->isChecked());
+	s.setValue("forceMining", ui->forceMining->isChecked());
 	s.setValue("paranoia", ui->paranoia->isChecked());
 	s.setValue("showAll", ui->showAll->isChecked());
 	s.setValue("showAllAccounts", ui->showAllAccounts->isChecked());
@@ -529,6 +530,7 @@ void Main::readSettings()
 	ui->upnp->setChecked(s.value("upnp", true).toBool());
 	ui->forceAddress->setText(s.value("forceAddress", "").toString());
 	ui->usePast->setChecked(s.value("usePast", true).toBool());
+	ui->forceMining->setChecked(s.value("forceMining", false).toBool());
 	ui->paranoia->setChecked(s.value("paranoia", false).toBool());
 	ui->showAll->setChecked(s.value("showAll", false).toBool());
 	ui->showAllAccounts->setChecked(s.value("showAllAccounts", false).toBool());

alethzero/MainWin.h

@@ -125,7 +125,7 @@ private slots:
 	void on_showAllAccounts_triggered() { refreshAccounts(); }
 	void on_loadJS_triggered();
 	void on_blockChainFilter_textChanged();
-	void on_clearPending_triggered();
+	void on_forceMining_triggered();
 	void on_dumpTrace_triggered();
 	void on_dumpTraceStorage_triggered();
 	void on_dumpTracePretty_triggered();

libethcore/CommonEth.cpp

@@ -29,7 +29,7 @@ using namespace eth;
 
 //#define ETH_ADDRESS_DEBUG 1
 
-const unsigned eth::c_protocolVersion = 24;
+const unsigned eth::c_protocolVersion = 25;
 const unsigned eth::c_databaseVersion = 1;
 
 static const vector<pair<u256, string>> g_units =

libethereum/Client.cpp

@@ -388,7 +388,7 @@ void Client::work(bool _justQueue)
 	h256Set changeds;
 
 	// Do some mining.
-	if (!_justQueue)
+	if (!_justQueue && (m_pendingCount || m_forceMining))
 	{
 
 		// TODO: Separate "Miner" object.
@@ -455,6 +455,11 @@ void Client::work(bool _justQueue)
 			this_thread::sleep_for(chrono::milliseconds(100));
 		}
 	}
+	else
+	{
+		cwork << "SLEEP";
+		this_thread::sleep_for(chrono::milliseconds(100));
+	}
 
 	// Synchronise state to block chain.
 	// This should remove any transactions on our queue that are included within our state.
@@ -503,6 +508,7 @@ void Client::work(bool _justQueue)
 				cnote << "Additional transaction ready: Restarting mining operation.";
 			m_restartMining = true;
 		}
+		m_pendingCount = m_postMine.pending().size();
 	}
 
 	cwork << "noteChanged" << changeds.size() << "items";

libethereum/Client.h

@@ -295,6 +295,9 @@ public:
 	/// Get and clear the mining history.
 	std::list<MineInfo> miningHistory() { auto ret = m_mineHistory; m_mineHistory.clear(); return ret; }
 
+	bool forceMining() const { return m_forceMining; }
+	void setForceMining(bool _enable) { m_forceMining = _enable; }
+
 	/// Clears pending transactions. Just for debug use.
 	void clearPending();
 
@@ -347,9 +350,11 @@ private:
 
 	bool m_paranoia = false;
 	bool m_doMine = false;					///< Are we supposed to be mining?
+	bool m_forceMining = false;				///< Mine even when there are no transactions pending?
 	MineProgress m_mineProgress;
 	std::list<MineInfo> m_mineHistory;
 	mutable bool m_restartMining = false;
+	mutable unsigned m_pendingCount = 0;
 
 	mutable std::mutex m_filterLock;
 	std::map<h256, InstalledFilter> m_filters;

libethereum/State.cpp

@@ -681,7 +681,7 @@ void State::commitToMine(BlockChain const& _bc)
 {
 	uncommitToMine();
 
-	cnote << "Commiting to mine on block" << m_previousBlock.hash;
+	cnote << "Committing to mine on block" << m_previousBlock.hash;
 #ifdef ETH_PARANOIA
 	commit();
 	cnote << "Pre-reward stateRoot:" << m_state.root();