bitcoin/bitcoin — pull request #980 by Diapolo (2012-03-23 12:51:12+00:00)
Title: Fix for #956 (GUI freeze on Windows)

Okay, so my former assumption boost 1.47 would fix #956 was wrong and boost 1.49 did not fix it either. It turns out, that I could recreate the error condition by running Bitcoin-Qt and simply switch of my PC. So there were the 2 orphan files from boost interprocess that cause the problem.

I found out, that no interprocess_exception was thrown, not in qtipcserver.cpp and not in bitcoin.cpp. Next step was to look through the code and the "create_or_open" option in the message_queue constructor got my attention. I changed this to create_only and voila there was an exception I could work with. It sais "file already exists", which makes sens as there are those orphan files left.

In the end I introduced a new ipcRecover() function, which is called after catching interprocess::already_exists_error. This function works with the path were the stale message queue file "BitcoinURL" resides and checks if the file is there and tries to remove it. If that succeeds the function returns true and ipcInit() is called again. If this fails an error is written to the debug.log.

Test case with 1.47 boost libs:
- kill running Bitcoin-Qt instance by switching PC of
- check for stale files, which are there

- starting the client again with the fix disabled in the code
- no exception, no log entries and a frozen GUI

- starting the client again with fix enabled results in a not frozen GUI and normal client operation

Log:
ipcInit - boost interprocess exception #9: File exists.
ipcRecover - old message queue found, trying to remove C:\ProgramData\boost_interprocess\BitcoinURL ...success

I know there are many commits in here, so I would suggest to first only look at the diff and if you are interested in the history of the fix take a look at the commits itself.

As I only run Windows the Linux / Mac devs should test this code, during our discussion.