From 951793fd9f218151695f8f5a58d292c045df4541 Mon Sep 17 00:00:00 2001
From: deanlee <deanlee3@gmail.com>
Date: Fri, 29 Mar 2024 15:47:48 +0800
Subject: [PATCH] reserve

---
 can/common.h  | 1 +
 can/parser.cc | 8 ++++++++
 2 files changed, 9 insertions(+)

diff --git a/can/common.h b/can/common.h
index 16b2e808ed..b462528441 100644
--- a/can/common.h
+++ b/can/common.h
@@ -67,6 +67,7 @@ class CANParser {
   const int bus;
   const DBC *dbc = NULL;
   std::unordered_map<uint32_t, MessageState> message_states;
+  int32_t signal_count = -1;
 
 public:
   bool can_valid = false;
diff --git a/can/parser.cc b/can/parser.cc
index 832948d1c7..d70cc1bc03 100644
--- a/can/parser.cc
+++ b/can/parser.cc
@@ -2,6 +2,7 @@
 #include <cassert>
 #include <cstring>
 #include <limits>
+#include <numeric>
 #include <stdexcept>
 #include <sstream>
 
@@ -257,6 +258,13 @@ void CANParser::query_latest(std::vector<SignalValue> &vals, uint64_t last_ts) {
   if (last_ts == 0) {
     last_ts = last_nanos;
   }
+
+  if (signal_count == -1) {
+    signal_count = std::accumulate(message_states.cbegin(), message_states.cend(), 0, [](int n, auto &it) {
+      return n + it.second.parse_sigs.size();
+    });
+  }
+  vals.reserve(signal_count);
   for (auto& kv : message_states) {
     auto& state = kv.second;
     if (last_ts != 0 && state.last_seen_nanos < last_ts) {