[GitHub] [arrow] pitrou commented on a change in pull request #12437: ARROW-14908: [C++][R] Multiple scanners plus join gives segfault when use_threads=FALSE

[GitBox <gi...@apache.org>]

pitrou commented on a change in pull request #12437:
URL: https://github.com/apache/arrow/pull/12437#discussion_r809190891



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File path: cpp/src/arrow/compute/exec/hash_join.cc
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@@ -896,6 +896,17 @@ class HashJoinBasicImpl : public HashJoinImpl {
     std::vector<uint8_t> has_match;
   };
   std::vector<ThreadLocalState> local_states_;
+  ThreadLocalState& GetLocalState(size_t thread_index) {
+    if (ARROW_PREDICT_FALSE(thread_index >= local_states_.size())) {
+      size_t old_size = local_states_.size();
+      local_states_.resize(thread_index + 1);
+      for (size_t i = old_size; i < local_states_.size(); ++i) {
+        local_states_[i].is_initialized = false;
+        local_states_[i].is_has_match_initialized = false;
+      }
+    }
+    return local_states_[thread_index];
+  }

Review comment:
       Isn't this thread-unsafe? You're resizing a vector while it could be accessed by other threads concurrently?




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