[lldb-dev] ConnectionFileDescriptor and thread safety

[Greg Clayton]

The mutex is just to stop multiple threads from reading right now. One thread locks the mutex and gets to read and the other thread will fail instead of blocking. What is hard to understand about this?



> On Oct 2, 2014, at 2:22 PM, Zachary Turner <zturner at google.com> wrote:
> 
> What are the thread safety assumptions of ConnectionFileDescriptor?  There's a mutex in ConnectionFileDescriptor::Read(), but it almost seems pointless.  All it does is do a TryLock() and then return an error if it fails.  I sincerely doubt anyone is actually handling this error, so this implies to me that it's intended to not be used concurrently from multiple threads and this is just used to catch the error in case anyone messes up.
> 
> But this leads to something else that I don't understand.  Do we actually care to support regular on-disk files with this class, or do we only care about sockets and pipes?  We do seem to have support for a file://PATH connection string, so someone thinks this is useful.  But how would it even work without being able to either seek or specify the offset?  Are you expected to use a different fd for the reading and writing side and never mix calls to Read() and Write() on the same Connection instance?  If so, maybe we need to make this explicit with InboundConnection and OutboundConnection or something like that.
> 
>