Boost.Asio TCP连接多线程访问的线程安全问题咨询

1. Do we need a lock for ConnectionHandler::total_sum_? #

Nope, you don’t need any locking here. Here’s why:

• Boost.Asio enforces that asynchronous handlers tied to a single socket will never run concurrently. In your code flow, you only kick off the next async_read after the previous one has finished processing (you call read_packet() at the end of process_data()). This means the code that modifies total_sum_ in process_data() will never execute in parallel with itself or any other handler for the same ConnectionHandler.
• Even with a thread pool running your io_service, the service ensures that handlers for a single connection are executed sequentially. There’s no race condition on total_sum_ because all writes to it happen one after another, not at the same time.

2. Is reusing ConnectionHandler::received_data_ as the read buffer safe? #

Absolutely—this is a safe and common pattern in Boost.Asio code. Here’s the breakdown:

• The async_read operation won’t call your process_data() handler until it’s fully read a Data_t into received_data_. You can be sure the buffer holds valid data once process_data() runs.
• You only start the next async_read after you’ve finished using the current data in process_data() (by invoking read_packet() at the end). This means the next read won’t overwrite received_data_ until you’re done with the current value.
• There’s no overlap between reading into the buffer and processing its contents, so reusing the same buffer instance is totally safe.

内容的提问来源于stack exchange，提问作者Jason