Group.__init() should be parallelised

• Bitbucket: https://bitbucket.org/hpk42/execnet/issue/28
• Originally reported by: @crusaderky
• Originally created at: 2014-01-22T16:51:21.959

Consider the following snippet:

hosts = [...list of hosts...]
group = execnet.Group(("ssh %s" % host for host in hosts))
group.remote_exec(something)

Imagine having a grid of 200 hosts.
While Group.remote_exec() will run on all the hosts in parallel, Group.__init__() will connect via ssh to each one of them, serially. On a typical LAN, this easily accounts to minutes.

I attach a patch for multi.py (on top of the latest hg commit) that is intended to fix the problem. However, with that patch the program deadlocks in gateway_base.py, line 360, and I can't figure out the reason.

从 multi.py 中的 Group.init 开始，检查 gateway_base.py 约第 360 行附近的代码，报告中的补丁会在那里造成死锁。使用许多 SSH 网关重现初始化过程，并将行为与附加的补丁进行比较。完成标准是：Group 初始化能够并行连接到主机而不会发生死锁，同时 Group.remote_exec() 仍能正常工作。