[sheepdog] [sheepdog/sheepdog] 1c0f71: lib: exponential backoff in request retry

[Hitoshi Mitake]

Branch: refs/heads/exp-backoff
Home: https://github.com/sheepdog/sheepdog
Commit: 1c0f71c9fa78c499a9927e6f7558ba7d104055f8
https://github.com/sheepdog/sheepdog/commit/1c0f71c9fa78c499a9927e6f7558ba7d104055f8
Author: Hitoshi Mitake <***@lab.ntt.co.jp>
Date: 2017-02-15 (Wed, 15 Feb 2017)

Changed paths:
M dog/Makefile.am
M include/net.h
M lib/net.c
M shepherd/Makefile.am

Log Message:
-----------
lib: exponential backoff in request retry

Current sheepdog resend a request after timeout immediately. It isn't
good for avoiding high load spikes: requests that come in a short time
interval will be resent at the almost same time. This commit adds a
mechanism of exponential backoff [1] for distributing the retry
pressure.

[1] https://www.awsarchitectureblog.com/2015/03/backoff.html

Signed-off-by: Hitoshi Mitake <***@lab.ntt.co.jp>