Merge pull request #4395 from taosdata/hotfix/TD-2287

Hotfix/td 2287

src/rpc/src/rpcMain.c

@@ -630,8 +630,16 @@ static void rpcReleaseConn(SRpcConn *pConn) {
   } else {
     // if there is an outgoing message, free it
     if (pConn->outType && pConn->pReqMsg) {
-      if (pConn->pContext) pConn->pContext->pConn = NULL; 
-      taosRemoveRef(tsRpcRefId, pConn->pContext->rid);
+      SRpcReqContext *pContext = pConn->pContext;
+      if (pContext->pRsp) {   
+        // for synchronous API, post semaphore to unblock app
+        pContext->pRsp->code = TSDB_CODE_RPC_APP_ERROR;
+        pContext->pRsp->pCont = NULL;
+        pContext->pRsp->contLen = 0;
+        tsem_post(pContext->pSem);
+      }
+      pContext->pConn = NULL; 
+      taosRemoveRef(tsRpcRefId, pContext->rid);
     }
   }