Fix PID capture to get actual Java process, not wrapper

Use pgrep to find the actual Java child process instead of using
the bash wrapper PID. This ensures perf attaches to the correct
process.

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

Author: jbachorik

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

@@ -100,18 +100,24 @@ start_benchmark() {
          -r 100; done" \
          &> /tmp/renaissance_${benchmark}.log &
 
-    JAVA_PID=$!
-    echo ${JAVA_PID} > /tmp/java_perf_test.pid
+    local WRAPPER_PID=$!
+    echo ${WRAPPER_PID} > /tmp/java_perf_test_wrapper.pid
 
-    log_info "Java process started with PID: ${JAVA_PID}"
+    log_info "Benchmark wrapper started with PID: ${WRAPPER_PID}"
 
-    # Verify process started successfully
-    sleep 2
-    if ! kill -0 ${JAVA_PID} 2>/dev/null; then
-        log_error "Java process ${JAVA_PID} died immediately. Check /tmp/renaissance_${benchmark}.log"
+    # Wait for Java process to actually start and get its PID
+    sleep 3
+    JAVA_PID=$(pgrep -P ${WRAPPER_PID} java)
+
+    if [ -z "${JAVA_PID}" ]; then
+        log_error "Could not find Java process. Check /tmp/renaissance_${benchmark}.log"
+        kill ${WRAPPER_PID} 2>/dev/null || true
         exit 1
     fi
 
+    echo ${JAVA_PID} > /tmp/java_perf_test.pid
+    log_info "Java process PID: ${JAVA_PID}"
+
     log_info "Warming up for ${WARMUP} seconds..."
     sleep ${WARMUP}
 
@@ -179,11 +185,22 @@ run_perf_record() {
 
 # Stop the benchmark
 stop_benchmark() {
+    # Kill wrapper process which will kill Java too
+    if [ -f /tmp/java_perf_test_wrapper.pid ]; then
+        local wrapper_pid=$(cat /tmp/java_perf_test_wrapper.pid)
+        log_info "Stopping benchmark wrapper ${wrapper_pid}..."
+        kill ${wrapper_pid} 2>/dev/null || true
+        sleep 2
+        kill -9 ${wrapper_pid} 2>/dev/null || true
+        rm -f /tmp/java_perf_test_wrapper.pid
+    fi
+
+    # Also kill Java process directly
     if [ -f /tmp/java_perf_test.pid ]; then
         local pid=$(cat /tmp/java_perf_test.pid)
         log_info "Stopping Java process ${pid}..."
         kill ${pid} 2>/dev/null || true
-        sleep 2
+        sleep 1
         kill -9 ${pid} 2>/dev/null || true
         rm -f /tmp/java_perf_test.pid
     fi