HPCC-16064 Log stalled splitter outputs

Signed-off-by: Jake Smith <jake.smith@lexisnexis.com>

thorlcr/activities/nsplitter/thnsplitterslave.cpp

@@ -84,6 +84,7 @@ class NSplitterSlaveActivity : public CSlaveActivity, implements ISharedSmartBuf
     bool writeBlocked = false, pagedOut = false;
     CriticalSection connectLock, prepareInputLock, writeAheadCrit;
     PointerArrayOf<Semaphore> stalledWriters;
+    UnsignedArray stalledWriterIdxs;
     unsigned stoppedOutputs = 0;
     unsigned activeOutputs = 0;
     rowcount_t recsReady = 0;
@@ -155,6 +156,7 @@ public:
         recsReady = 0;
         writeBlocked = false;
         stalledWriters.kill();
+        stalledWriterIdxs.kill();
         ForEachItemIn(o, outputs)
         {
             CSplitterOutput *output = (CSplitterOutput *)outputs.item(o);
@@ -240,8 +242,20 @@ public:
             else if (writeBlocked) // NB: only used by 'balanced' splitter, which blocks write when too far ahead
             {
                 stalledWriters.append(&writeBlockSem);
-                CriticalUnblock ub(writeAheadCrit);
-                writeBlockSem.wait(); // when active writer unblocks, signals all stalledWriters
+                stalledWriterIdxs.append(outIdx);
+                loop
+                {
+                    {
+                        CriticalUnblock ub(writeAheadCrit);
+                        if (writeBlockSem.wait(60000)) // when active writer unblocks, signals all stalledWriters
+                            break;
+                    }
+                    ForEachItemIn(i, stalledWriterIdxs)
+                    {
+                        unsigned idx = stalledWriterIdxs.item(i);
+                        ActPrintLog("Splitter output(%d) stalled on writeahead", idx);
+                    }
+                }
                 // recsReady or eofHit will have been updated by the blocking thread by now, loop and re-check
             }
             else