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Lock the sender map read in ProducerClient::GetSender

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#7,285 0 commenti 0 reazioni 1 assegnatario Vedi su GitHub

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Dal 5/8/2026.

Valutazione

Questa issue non è ancora stata valutata.

Descrizione

Event Hubs

Summary

ProducerClient::GetSender reads the sender map with no lock. EnsureSender changes the same map under m_sendersLock. Two threads that send to different partitions for the first time cause a data race. One thread reads a std::map while the other thread writes it. This is undefined behavior. Send and CreateBatch both use this path.

Parent: #7284. Severity tags follow the key in #7252. The code anchors refer to commit 2de7c583e.

Motivation

GetSender has three lines and takes no lock (src/producer_client.cpp:259-263):

Azure::Core::Amqp::_internal::MessageSender ProducerClient::GetSender(
    std::string const& partitionId)
{
  return m_senders.at(partitionId);
}

EnsureSender writes to the same map under m_sendersLock (src/producer_client.cpp:229-257). A write can rebalance the red-black tree that holds a std::map. A parallel at() call then reads that tree while it moves.

ProducerClient::Send calls GetSender in its retry lambda (src/producer_client.cpp:111). CreateBatch calls it at src/producer_client.cpp:90. Both callers call EnsureSender first, so one thread alone is safe. Two threads with different partitions are not safe. Thread A can write the sender for partition 1 while thread B reads the sender for partition 0.

GetSession takes m_sessionsLock for the same pattern. The missing lock in GetSender therefore looks like an error.

Proposal

  • Take m_sendersLock in ProducerClient::GetSender before it reads m_senders (src/producer_client.cpp:259-263). [GA blocker]
  • Examine ConsumerClient for the same pattern on m_receivers and m_receiversLock (inc/azure/messaging/eventhubs/consumer_client.hpp:206). [GA blocker]

This is the smallest correct change. It keeps all the signatures. The method releases the lock before the caller uses the MessageSender handle. The method returns the handle by value, so no reference stays alive after the lock. #7288 replaces this mutex with a std::shared_mutex later. Do this change first, because it is small and it stops the undefined behavior now.

Validation

  • The thread sanitizer reports no race. Use N threads. Each thread sends to a different partition that no thread used before.
  • The same test causes a thread sanitizer error before the change.
  • The Event Hubs unit tests pass.
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