multiple paralel peek piece operations per torrent not currently supported.

return invalid handle ("busy, try again" for peekpost RPC) for subsequent requests,
until current operation completes and torrent is freed.

src/bitcoinrpc.h

@@ -50,6 +50,7 @@ enum RPCErrorCode
     RPC_DESERIALIZATION_ERROR       = -22, // Error parsing or validating structure in raw format
     RPC_FORBIDDEN_ON_PUBLIC_SERVER  = -23, // public server mode is activated, this method is not allowed
     RPC_TIMEOUT                     = -24, // timeout on resource retrieval
+    RPC_RESOURCE_BUSY_TRY_AGAIN     = -25, // Resource is currently busy, try again later
 
     // P2P client errors
     RPC_CLIENT_NOT_CONNECTED        = -9,  // Bitcoin is not connected

src/twister.cpp

@@ -57,6 +57,7 @@ static map<std::string, bool> m_specialResources;
 enum ExpireResType { SimpleNoExpire, NumberedNoExpire, PostNoExpireRecent };
 static map<std::string, ExpireResType> m_noExpireResources;
 static map<std::string, torrent_handle> m_userTorrent;
+static map<std::string, torrent_handle> m_peekTorrent;
 static boost::scoped_ptr<CLevelDB> m_swarmDb;
 static int m_threadsToJoin;
 
@@ -147,6 +148,14 @@ torrent_handle startTorrentUser(std::string const &username, bool following, int
     torrent_handle h;
 
     LOCK(cs_twister);
+    if( m_peekTorrent.count(username) ) {
+        /* multiple paralel peek piece operations per torrent not 
+         * currently supported. return invalid handle for subsequent
+         * requests, until current operation completes and torrent
+         * is freed. */
+         return torrent_handle();
+    }
+
     if( !m_userTorrent.count(username) || peek_single_piece >= 0 ) {
         sha1_hash ih = dhtTargetHash(username, "tracker", "m");
 
@@ -166,8 +175,10 @@ torrent_handle startTorrentUser(std::string const &username, bool following, int
         load_file(filename.c_str(), tparams.resume_data);
 
         h = ses->add_torrent(tparams);
-        if( peek_single_piece == -1 ) {
+        if( peek_single_piece < 0 ) {
             m_userTorrent[username] = h;
+        } else {
+            m_peekTorrent[username] = h;
         }
         if( !following ) {
             h.auto_managed(true);
@@ -898,19 +909,26 @@ void ThreadSessionAlerts()
 
                 save_resume_data_alert const* rda = alert_cast<save_resume_data_alert>(*i);
                 if (rda) {
-                    num_outstanding_resume_data--;
-                    if (!rda->resume_data) continue;
-
+                    if (rda->resume_data) {
                         torrent_handle h = rda->handle;
                         torrent_status st = h.status(torrent_handle::query_save_path);
                         std::vector<char> out;
                         bencode(std::back_inserter(out), *rda->resume_data);
                         save_file(combine_path(st.save_path, to_hex(st.info_hash.to_string()) + ".resume"), out);
                     }
+                }
 
-                if (alert_cast<save_resume_data_failed_alert>(*i))
+                save_resume_data_failed_alert const *rdfa = alert_cast<save_resume_data_failed_alert>(*i);
+                if (rda || rdfa)
                 {
-                    --num_outstanding_resume_data;
+                    torrent_handle h = (rda) ? rda->handle : rdfa->handle;
+                    torrent_status st = h.status();
+                    LOCK(cs_twister);
+                    num_outstanding_resume_data--;
+                    if(m_peekTorrent.count(st.name) && st.paused) {
+                        m_peekTorrent.erase(st.name);
+                        ses->remove_torrent(h);
+                    }
                 }
 
                 external_ip_alert const* ei = alert_cast<external_ip_alert>(*i);
@@ -2350,7 +2368,9 @@ Value newdirectmsg(const Array& params, bool fHelp)
         }
 
         torrent_handle h = startTorrentUser(strFrom, true);
+        if( h.is_valid() ) {
             h.add_piece(k++,buf.data(),buf.size());
+        }
 
         hexcapePost(v);
         ret = entryToJson(v);
@@ -3861,7 +3881,9 @@ static void signAndAddDM(const std::string &strFrom, int k, const entry *dm)
         throw JSONRPCError(RPC_INVALID_PARAMS,errmsg);
 
     torrent_handle h = startTorrentUser(strFrom, true);
+    if( h.is_valid() ) {
         h.add_piece(k++,buf.data(),buf.size());
+    }
 }
 
 Value newgroupinvite(const Array& params, bool fHelp)
@@ -4102,7 +4124,7 @@ Value peekpost(const Array& params, bool fHelp)
         h = startTorrentUser(strUsername,true,k);
 
         // this loop receives alerts from both dht network and torrent peek extension
-        while( am.wait_for_alert(timeToWait) ) {
+        while( h.is_valid() && am.wait_for_alert(timeToWait) ) {
             std::auto_ptr<alert> a(am.get());
 
             dht_reply_data_alert const* rd = alert_cast<dht_reply_data_alert>(&(*a));
@@ -4126,8 +4148,12 @@ Value peekpost(const Array& params, bool fHelp)
             }
         }
 
-        if( h.is_valid() )
-            ses->remove_torrent(h);
+        if( h.is_valid() ) {
+            LOCK(cs_twister);
+            h.pause();
+            h.save_resume_data();
+            num_outstanding_resume_data++;
+        }
 
         if( !DhtProxy::fEnabled ) {
             dhtgetMapRemove(ih,&am);
@@ -4152,7 +4178,11 @@ Value peekpost(const Array& params, bool fHelp)
             }
         }
     } else {
+        if(h.is_valid()) {
             throw JSONRPCError(RPC_TIMEOUT, "timeout or post not found");
+        } else {
+            throw JSONRPCError(RPC_RESOURCE_BUSY_TRY_AGAIN, "resource busy, try again");
+        }
     }
 
     return ret;