aws-sdk-ruby: aws-sdk-s3 upload fails with Deadlock

Issue description

When uploading a file, a deadlock is thrown by the multipart-upload method

[2] pry(main)> obj.upload_file(path)
fatal: No live threads left. Deadlock?
from /opt/chef/embedded/lib/ruby/gems/2.3.0/gems/aws-sdk-s3-1.12.0/lib/aws-sdk-s3/multipart_file_uploader.rb:145:in `value'

Gem name (‘aws-sdk’, ‘aws-sdk-resources’ or service gems like ‘aws-sdk-s3’) and its version

aws-sdk-core (3.20.2)
aws-sdk-kms (1.5.0)
aws-sdk-s3 (1.10.0)

Version of Ruby, OS environment

ruby 2.1.3p242 (2014-09-19 revision 47630) [x86_64-linux-gnu]
centos 6.9

Code snippets / steps to reproduce

def upload_backup(path)
   s3 = Aws::S3::Resource.new(region: 'us-east-1')
   filename = File.basename(path)
   bucket = s3.bucket('myBackups')
   raise BackupAlreadyExistsOnS3, "file already exists in s3 #{filename}" if 
   bucket.object(filename).exists?
   obj = bucket.object(filename)
   puts "Beginning File Upload (#{filename})".light_blue
   obj.upload_file(path)
   puts "File Upload Successful (#{filename})".green
end