locking: add a quick example of GUARDED_BY

This was chosen not because it's necessarily helpful, but because its locking
assumptions were already correct.

src/main.cpp

@@ -72,9 +72,9 @@ struct COrphanTx {
     CTransaction tx;
     NodeId fromPeer;
 };
-map<uint256, COrphanTx> mapOrphanTransactions;
-map<uint256, set<uint256> > mapOrphanTransactionsByPrev;
-void EraseOrphansFor(NodeId peer);
+map<uint256, COrphanTx> mapOrphanTransactions GUARDED_BY(cs_main);;
+map<uint256, set<uint256> > mapOrphanTransactionsByPrev GUARDED_BY(cs_main);;
+void EraseOrphansFor(NodeId peer) EXCLUSIVE_LOCKS_REQUIRED(cs_main);
 
 /**
  * Returns true if there are nRequired or more blocks of minVersion or above
@@ -523,7 +523,7 @@ CBlockTreeDB *pblocktree = NULL;
 // mapOrphanTransactions
 //
 
-bool AddOrphanTx(const CTransaction& tx, NodeId peer)
+bool AddOrphanTx(const CTransaction& tx, NodeId peer) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
 {
     uint256 hash = tx.GetHash();
     if (mapOrphanTransactions.count(hash))
@@ -553,7 +553,7 @@ bool AddOrphanTx(const CTransaction& tx, NodeId peer)
     return true;
 }
 
-void static EraseOrphanTx(uint256 hash)
+void static EraseOrphanTx(uint256 hash) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
 {
     map<uint256, COrphanTx>::iterator it = mapOrphanTransactions.find(hash);
     if (it == mapOrphanTransactions.end())
@@ -587,7 +587,7 @@ void EraseOrphansFor(NodeId peer)
 }
 
 
-unsigned int LimitOrphanTxSize(unsigned int nMaxOrphans)
+unsigned int LimitOrphanTxSize(unsigned int nMaxOrphans) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
 {
     unsigned int nEvicted = 0;
     while (mapOrphanTransactions.size() > nMaxOrphans)
@@ -3783,7 +3783,7 @@ std::string GetWarnings(const std::string& strFor)
 //
 
 
-bool static AlreadyHave(const CInv& inv)
+bool static AlreadyHave(const CInv& inv) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
 {
     switch (inv.type)
     {