DRb.start_service(nil) is very slow
On some systems - such as mine - DRB.start_service(nil) is very slow. This is caused by the fact that DRb.open_server calls TCPServer.open(nil, 0).addr. On my system, this takes about 3 seconds, and during those 3 seconds there is 0% CPU usage.
I suspect it has got something to do with the fact that retrieving the port of a server socket that's bound to 0.0.0.0 is for some unknown reason very slow.
The problem can be fixed by replacing the following line in drb.rb
uri = 'druby://:0' unless uri
uri = 'druby://localhost:0' unless uri
This does not violate DRb.start_service's contract, because a nil indicates that it will bind to the default local host name.
The following monkeypatch works around the issue:
class << self
alias orig_start_service start_service
def self.start_service(uri = nil, front = nil, config = nil) if uri.nil? orig_start_service("druby://localhost:0", front, config) else orig_start_service(uri, front, config) end end
#1 Updated by Brian Candler over 8 years ago
I suspect a DNS/hostname resolution problem on your system.
Looking at 1.8.6p114, notice that DRbTCPSocket.getservername first calls Socket.gethostname to get the hostname, then calls Socket.gethostbyname which does both forward and reverse name resolution, presumably to map to a "canonical" name. Then DRbTCPSocket.open_server_inaddr_any also calls Socket.getaddrinfo, although it discards the results apart from using them to decide whether to bind to IPv4, IPv6, or both.
Try the following in irb - how long does each step take?
h1 = Socket.gethostname
h2 = Socket.gethostbyname(h1)
Socket.getaddrinfo(h2, nil, Socket::AF_UNSPEC, Socket::SOCK_STREAM, 0, Socket::AI_PASSIVE)
If one of these steps is slow, you may be able to solve the problem by adding an entry in /etc/resolv.conf to map your hostname to your primary interface IP.
#3 Updated by Brian Candler over 8 years ago
OK, how about this:
t = TCPServer.new("", nil)
On my machine, the first 't.addr' invocations take about 5 seconds. The last one is instant. I believe this is because of the delay looking up 0.0.0.0 in the DNS.