Protect access to IsCompiled

Make sure that IsCompiled is only set once the TStreamerInfo is
actually compiled. Also, make sure to lock and then check the value
again to avoid two threads from recompiling the same object.

io/io/src/TBufferFile.cxx

@@ -3684,10 +3684,14 @@ Int_t TBufferFile::ReadClassBuffer(const TClass *cl, void *pointer, Int_t versio
             return 0;            
          }
       } else if (!sinfo->IsCompiled()) {
-         // Streamer info has not been compiled, but exists.
-         // Therefore it was read in from a file and we have to do schema evolution.
-         const_cast<TClass*>(cl)->BuildRealData(pointer);
-         sinfo->BuildOld();
+	 //See if another thread beat us to it
+         R__LOCKGUARD(gCINTMutex);
+	 if(!sinfo->IsCompiled()) {
+	    // Streamer info has not been compiled, but exists.
+	    // Therefore it was read in from a file and we have to do schema evolution.
+	    const_cast<TClass*>(cl)->BuildRealData(pointer);
+	    sinfo->BuildOld();
+	 }
       }
    }
 
@@ -3830,8 +3834,12 @@ Int_t TBufferFile::WriteClassBuffer(const TClass *cl, void *pointer)
 	 sinfo->Build();
       }
    } else if (!sinfo->IsCompiled()) {
-      const_cast<TClass*>(cl)->BuildRealData(pointer);
-      sinfo->BuildOld();
+      //see if another thread beat us to it
+      R__LOCKGUARD(gCINTMutex);
+      if(!sinfo->IsCompiled()) {
+	const_cast<TClass*>(cl)->BuildRealData(pointer);
+	sinfo->BuildOld();
+      }
    }
 
    //write the class version number and reserve space for the byte count

io/io/src/TStreamerInfoActions.cxx

@@ -2247,6 +2247,15 @@ static TConfiguredAction GetCollectionWriteAction(TVirtualStreamerInfo *info, TS
    return TConfiguredAction();
 }
 
+namespace {
+  class SetCompiled {
+  private:
+    TStreamerInfo* fInfo;
+  public:
+    SetCompiled(TStreamerInfo* iInfo): fInfo(iInfo) {}
+    ~SetCompiled() { fInfo->SetBit(TStreamerInfo::kIsCompiled); }
+  };
+}
 
 //______________________________________________________________________________
 void TStreamerInfo::Compile()
@@ -2300,7 +2309,7 @@ void TStreamerInfo::Compile()
    fOffset = new Int_t[ndata+1];
    fType   = new Int_t[ndata+1];
 
-   SetBit(kIsCompiled);
+   SetCompiled setCompiledWhenFinished(this);
    if (!fReadObjectWise) fReadObjectWise = new TStreamerInfoActions::TActionSequence(this,ndata);
    if (!fWriteObjectWise) fWriteObjectWise = new TStreamerInfoActions::TActionSequence(this,ndata);