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The fifo_reader thread function and the function select.cc:peek_fifo() can both change the state of a fifo_client_handler. These changes are made under fifo_client_lock, so there is no race, but the changes can still be incompatible. Add code to make sure that only one of these functions can change the state from its initial fc_listening state. Whichever function does this calls the fhandler_fifo::record_connection method, which is now public so that peek_fifo can call it. Slightly modify that method to make it suitable for being called by peek_fifo. Make a few other small changes to the fifo_reader thread function to change how it deals with the STATUS_PIPE_CLOSING value that can (rarely) be returned by NtFsControlFile. Add commentary to fhandler_fifo.cc to explain fifo_client connect states and where they can be changed.
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