From 339958ea75660b5fe50bb8e54dc90c2618ef2924 Mon Sep 17 00:00:00 2001
From: Steven Doran <78985334+S81D@users.noreply.github.com>
Date: Wed, 14 Jan 2026 10:29:15 -0600
Subject: [PATCH] Update LoadReweightGenieEvent.cpp

Some events have parameter throws that make the xsec_total < 0. Add error handling to account for events where re-weighting failed. An example of what sometimes happens:

Executing tool LoadWCSim with MC entry 20, trigger 0
Analyse: GReWeightXSecMEC.cxx:500: double genie::rew::GReWeightXSecMEC::CalcWeightPNDelta(const genie::EventRecord&): Assertion `xsec_tot > 0.' failed.
Aborted (core dumped)

This causes the toolchain to crash at entry N, leading to a large loss in statistics. To remedy this we can use a recovery point where the weight will automatically be assigned as 1.0 if such a problematic value is sampled in multisim.
---
 .../LoadReweightGenieEvent.cpp                | 37 ++++++++++++++++++-
 1 file changed, 36 insertions(+), 1 deletion(-)

diff --git a/UserTools/LoadReweightGenieEvent/LoadReweightGenieEvent.cpp b/UserTools/LoadReweightGenieEvent/LoadReweightGenieEvent.cpp
index 85768367a..5af826f50 100644
--- a/UserTools/LoadReweightGenieEvent/LoadReweightGenieEvent.cpp
+++ b/UserTools/LoadReweightGenieEvent/LoadReweightGenieEvent.cpp
@@ -11,6 +11,21 @@
 //using namespace genie::constants;
 //using namespace genie::flux;
 
+// ***********************
+// GENIE ERROR HANDLING
+#include <csignal>
+#include <csetjmp>
+// global jump buffer for signal recovery
+static jmp_buf genie_jump_buffer;
+
+// signal handler function
+void handle_genie_abort(int sig) {
+    if (sig == SIGABRT) {
+        longjmp(genie_jump_buffer, 1);
+    }
+}
+// ***********************
+
 /*
 GENIE INPUTS
 ============
@@ -644,7 +659,27 @@ bool LoadReweightGenieEvent::Execute(){
 		// objects to compute the weights.
 		weights[i].resize( num_knobs );
 		for (unsigned int k = 0; k < num_knobs; ++k ) {
-			weights[i][k] = reweightVector[i].at(k).CalcWeight( *gevtRec );
+
+			// ERROR HANDLING FROM GENIE
+			// ************************************
+			// register the signal handler
+            void (*prev_handler)(int) = std::signal(SIGABRT, handle_genie_abort);
+			
+			// set the jump point
+            if (setjmp(genie_jump_buffer) == 0) {
+                // default (if no error is present)
+                weights[i][k] = reweightVector[i].at(k).CalcWeight( *gevtRec );
+            } else {
+                // recovery path: if GENIE calls abort(), we land here
+                std::cerr << "!!! GENIE Aborted on event " << tchainentrynum
+                    << " (Knob: " << k << "). Skipping and using weight 1.0." << std::endl;
+                    weights[i][k] = 1.0;
+            }
+			
+            // restore the original handler
+            std::signal(SIGABRT, prev_handler);
+			// ************************************
+
 		}
 
 		reweights.insert(std::pair<std::string,std::vector<double>>(weight_names[i],weights[i]));