Observation

On Linux, a thread, hanging in boost::asio::serial_port::read_some does not std::thread::join after boost::asio::serial_port::close is called from another thread.

This applies to Boost v1.72.0 and v1.76.0 (other versions not tested).

The problem does not occur in Windows.

Sample Code

Starting a thread to synchronously read data from the serial port:

std::shared_ptr<std::thread> receivingThread = std::make_shared<std::thread>([this]() {
    LOG_TRACE(logger) << "Receiving thread started";
    try
    {
        size_t amountOfReceivedBytes = serialPort->read_some(boost::asio::buffer(receiveBuffer));
    }
    catch (std::exception &e)
    {
        LOG_WARN(logger) << "read_some interrupted " << e.what();
    }
    LOG_TRACE(logger) << "Receiving thread stopped";
});

Closing the serial port in the main thread:

// Close serial port.
if (serialPort && serialPort->is_open())
{
    serialPort->close();
    LOG_DEBUG(logger) << "Successfully closed the serial port.";
}
...
if (receivingThread)
{
    LOG_TRACE(logger) << "Waiting for receiving thread to finish.";
    receivingThread->join();
    LOG_TRACE(logger) << "Receiving thread finished.";
}
LOG_DEBUG(logger) << "Threads successfully stopped.";

The line LOG_TRACE(logger) << "Receiving thread finished."; is never reached.

Workaround

Detaching the thread

...
if (receivingThread)
{
    LOG_TRACE(logger) << "Detaching thread without waiting for it to finish.";
    receivingThread->detach();
    LOG_TRACE(logger) << "Thread detached.";
}
LOG_DEBUG(logger) << "Threads successfully stopped.";

serves as a workaround.

On Linux the lines

LOG_WARN(logger) << "read_some interrupted " << e.what();
LOG_TRACE(logger) << "Receiving thread stopped";

are never reached though, contrary to Windows, where they are reached! So I guess the thread is just forcefully killed by the OS eventually?!

See logs: elt-cpp-core-test-app_LINUX.log elt-cpp-core-test-app_WINDOWS.log

Possibly Related

Could be related to #762 and #779.

chriskohlhoff / asio

Thread performing synchronous read on serial port does not join after port is closed (Linux Only) #814

Observation

Sample Code

Workaround

Possibly Related