win_iocp_io_service hangs due to a race condition

[danielg@…]

The fix to #6321 introduced a bug that can cause the io_service to hang.

Example code (hangs eventually):

int main()
{
	for (;;)
	{
		boost::asio::io_service ios;
		ios.post([]{ std::cout << '.'; });

		boost::thread_group threads;
		for (size_t i = 0; i < 2; ++i)
			threads.create_thread([&]{ ios.run(); });
		threads.join_all();
	}
}

Suppose that one of the threads read the posted operation, completed it and got to the work_finished function where it decremented outstanding_work to 0 and entered the stop function. Now the second thread starts. In the run function it sees that outstanding_work is 0 so it sets stopped to 1 and returns. Back in the first thread PostQueuedCompletionStatus(iocp_.handle, 0, 0, 0) isn't called since stopped is already 1. do_one returns 1 and is called again. GetQueuedCompletionStatus returns WAIT_TIMEOUT because the operation queue is empty, which causes the loop to continue to the next iteration ad infinitum.

[danielg@…]

Proposed fix for this bug.

[chris_kohlhoff]

(In [82290]) Merge from trunk:

• Fix some 64-to-32-bit conversion warnings. Fixes #7459

• Fix typos in comments. Fixes #7761

• Fix error in example embedded in basic_socket::get_option's documentation. Fixes #7562

• Use long rather than int for SSL_CTX options, to match OpenSSL. Fixes #7209

• Use _snwprintf to address a compile error due to the changed swprintf signature in recent versions of MinGW. Fixes #7373

• Fix deadlock that can occur on Windows when shutting down a pool of io_service threads due to running out of work. Fixes #7552

• Enable noexcept qualifier for error categories. Fixes #7797

• Treat errors from accept as non-fatal. Fixes #7488

• Add a small block recycling optimisation.

• Version bump.

• Regenerate documentation.

[anonymous]

Is this fixed in boost 1.53.0 ?

I've noticed there are changes in win_iocp_io_service.ipp but not in the area pointed in the proposed patch, namely inside do_one() to prevent the infinite loop.

[chris_kohlhoff]

[82263]