Client thread safety

[miketsts]

Hi, @yhirose

Issue #492 states that the client is not thread safe.
Just few days later, you have implemented commit e022b8b which wraps ClientImpl::send() with two (!) mutex guards - request_mutex_ and socket_mutex_. Can we consider now that the thread safety has been provided?
I really want to send now requests to my server in asynchronous way. My alternative is to create a second client object for the second sending thread.

Thanks a lot!

[yhirose]

@miketsts, since ClientImpl::send() is now protected with request_mutext_, yes, it can be considered as thread safe. But the down side is that the second send() call will be blocked until the first call exits from std::lock_guard<std::recursive_mutex> request_mutex_guard(request_mutex_)... But it's guaranteed that the second request will reuse the same socket if the keep-alive condition is still met. If 'simultaneous' or concurrent requests are necessary, we still have to make another client objects. Hope this explanation helps!