Saver thisPacket handling in generic Output class, better documentation of internals

src/output/output.cpp

@@ -419,6 +419,9 @@ namespace Mist{
     return highest;
   }
  
+  /// Loads the page for the given trackId and keyNum into memory.
+  /// Overwrites any existing page for the same trackId.
+  /// Automatically calls thisPacket.null() if necessary.
   void Output::loadPageForKey(long unsigned int trackId, long long int keyNum){
     if (!myMeta.tracks.count(trackId) || !myMeta.tracks[trackId].keys.size()){
       WARN_MSG("Load for track %lu key %lld aborted - track is empty", trackId, keyNum);
@@ -469,6 +472,10 @@ namespace Mist{
     if (currKeyOpen.count(trackId) && currKeyOpen[trackId] == (unsigned int)pageNum){
       return;
     }
+    //If we're loading the track thisPacket is on, null it to prevent accesses.
+    if (thisPacket && thisPacket.getTrackId() == trackId){
+      thisPacket.null();
+    }
     char id[NAME_BUFFER_SIZE];
     snprintf(id, NAME_BUFFER_SIZE, SHM_TRACK_DATA, streamName.c_str(), trackId, pageNum);
     nProxy.curPage[trackId].init(id, DEFAULT_DATA_PAGE_SIZE);
@@ -786,7 +793,7 @@ namespace Mist{
   }
  
   ///Attempts to prepare a new packet for output.
-  ///If thisPacket evaluates to false, playback has completed.
+  ///If it returns true and thisPacket evaluates to false, playback has completed.
   ///Could be called repeatedly in a loop if you really really want a new packet.
   /// \returns true if thisPacket was filled with the next packet.
   /// \returns false if we could not reliably determine the next packet yet.
@@ -844,7 +851,9 @@ namespace Mist{
     //if we're going to read past the end of the data page, load the next page
     //this only happens for VoD
     if (nxt.offset >= nProxy.curPage[nxt.tid].len){
+      if (thisPacket){
         nxtKeyNum[nxt.tid] = getKeyForTime(nxt.tid, thisPacket.getTime());
+      }
       loadPageForKey(nxt.tid, ++nxtKeyNum[nxt.tid]);
       nxt.offset = 0;
       if (nProxy.curPage.count(nxt.tid) && nProxy.curPage[nxt.tid].mapped){
@@ -857,7 +866,6 @@ namespace Mist{
           buffer.insert(nxt);
         }
       }else{
-        thisPacket.null();
         dropTrack(nxt.tid, "page load failure", true);
       }
       return false;
@@ -898,7 +906,6 @@ namespace Mist{
       //The next key showed up on another page!
       //We've simply reached the end of the page. Load the next key = next page.
       loadPageForKey(nxt.tid, ++nxtKeyNum[nxt.tid]);
-      thisPacket.null();
       nxt.offset = 0;
       if (nProxy.curPage.count(nxt.tid) && nProxy.curPage[nxt.tid].mapped){
         unsigned long long nextTime = getDTSCTime(nProxy.curPage[nxt.tid].mapped, nxt.offset);

src/output/output.h

@@ -58,6 +58,8 @@ namespace Mist {
       uint32_t currTrackCount() const;
       virtual bool isReadyForPlay();
       //virtuals. The optional virtuals have default implementations that do as little as possible.
+      /// This function is called whenever a packet is ready for sending.
+      /// Inside it, thisPacket is guaranteed to contain a valid packet.
       virtual void sendNext() {}//REQUIRED! Others are optional.
       bool prepareNext();
       virtual void dropTrack(uint32_t trackId, std::string reason, bool probablyBad = true);