Fix Java process termination during perf record

Run benchmark in infinite loop to ensure process stays alive for
both perf stat and perf record measurements. Add process health
checks before each perf operation.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: jbachorik

ddprof-lib/benchmarks/branch-prediction/test_branch_prediction_perf.sh

@@ -89,14 +89,15 @@ start_benchmark() {
     log_info "Starting Renaissance benchmark: ${benchmark}"
 
     # Disable DD Java agent injection to avoid conflicts
-    # Run many iterations to keep benchmark running during perf measurement
+    # Run in infinite loop to ensure process stays alive during all perf measurements
+    # The benchmark will be killed by cleanup when tests complete
     env -u JAVA_TOOL_OPTIONS \
-    java -agentpath:"${PROFILER_LIB}=start,cpu,file=/tmp/test.jfr" \
+    bash -c "while true; do java -agentpath:\"${PROFILER_LIB}=start,cpu,file=/tmp/test.jfr\" \
          -Xmx2g \
          -Xms2g \
-         -jar "${RENAISSANCE_JAR}" \
-         "${benchmark}" \
-         -r 9999 \
+         -jar \"${RENAISSANCE_JAR}\" \
+         \"${benchmark}\" \
+         -r 100; done" \
          &> /tmp/renaissance_${benchmark}.log &
 
     JAVA_PID=$!
@@ -137,13 +138,25 @@ run_perf_stat() {
               2>&1 | tee "${output_file}"
 
     log_info "perf stat results saved to ${output_file}"
+
+    # Verify process is still alive
+    if ! kill -0 ${pid} 2>/dev/null; then
+        log_error "Process ${pid} died during perf stat. Check /tmp/renaissance_*.log"
+        return 1
+    fi
 }
 
 # Run perf record for detailed analysis
 run_perf_record() {
     local pid=$1
     local output_file="${2:-perf_record.data}"
 
+    # Verify process is still alive before starting
+    if ! kill -0 ${pid} 2>/dev/null; then
+        log_error "Process ${pid} is not running, skipping perf record"
+        return 1
+    fi
+
     log_info "Running perf record for ${DURATION} seconds..."
 
     perf record -e L1-icache-load-misses,branch-misses \