Greg Clayton <gclay...@apple.com> wrote on 16/02/2017 17:17:41: > We seem to have a race condition here. Any help figuring out what > that might be would be great.
I think I've now identified the problem. Normally in lldb-server when the child lldb-server process is launched inside GDBRemoteCommunication::StartDebugserverProcess the parent lldb-server waits for it to start up and write back the port is has selected to listen on a pipe. When lldb-server specifies a port for the child to listen on (when we start lldb-server with -P <port> or -m <minport> and -M <maxport>) then it doesn't bother setting up that pipe as it knows what the port will be. However not listening means the parent can reply to the lldb client with the port number before the debugserver process is actually up and and listening on that port. Simply making sure the pipe is always setup and used to read the port number from (even when lldb-server knows what it will be) ensures the child process is ready and allows me to connect reliably with an unmodified client lldb. The one second delay in the client was fixing things as inside PlatformRemoteGDBServer::DebugProcess there is a retry to ConnectRemote and the delay gave time for the child process to begin before the retry. This also explains why more people weren't seeing this problem as it only applies if you use the -P or -m/-M options. I think I only found those by searching the code, they don't appear in the help for lldb-server when you run it and I didn't manage to find any docs. Unless anyone points out a major flaw in the logic above I'll tidy up my fix and put a patch up on https://reviews.llvm.org/ in the next few days. The code for listening on a pipe from the child process is slightly different when __APPLE__ is defined so I need to verify the change on Mac and Linux. I'll probably just always read back the port and if it comes back as an unexpected value that may need to be a new error case. Would you mind if I also raised a patch to update the documentation to include the -P and -m/-M options? (Both in the help when you run lldb-server and on www/remote.html.) I originally came to this problem because another team couldn't connect to a remote system with only certain ports open and found them the options they needed by reading the source and I think doing things like connecting to processes in a VM or docker container where these options are needed are becoming more common. Thanks, Howard. Unless stated otherwise above: IBM United Kingdom Limited - Registered in England and Wales with number 741598. Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU
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